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GM Testing - Snap-on

1. DTC YEAR 4th VIN ENGINE DEFINITION 1996 B D Y 4 3 5 7 Vehicle speed output circuit A L N W 3 1 Fan relay 2 circuit fault 1996 97 F 5 7 Vehicle speed output circuit 1996 98 C F G H 3 8 Fan relay 2 circuit fault E K 4 6 1996 99 Lift dive output circuit P1652 G 4 0 1997 2000 Y 5 7 Chassis pitch fault 1999 C H W 3 8 Fan relay 2 circuit fault W 3 1 1999 Fan relay 2 amp 3 circuit N 3 4 1999 2001 F 3 8 Ride control circuit 1996 E K 4 6 A C clutch control circuit All others Low engine oil level lamp fault 1996 98 C G H 3 8 TCS delivered torque output circuit 1996 99 G 4 0 A C clutch control circuit P1653 F W 3 1 3 8 Fuel level output fault 1998 F 5 7 Low engine oil level lamp fault F 3 8 TCS delivered torque output circuit 1999 All others Fuel level output or low oil level lamp circuit 2000 01 All Low engine oil level lamp fault E K 4 6 1996 99 Cruise control disable circuit fault G 4 0 1996 98 All others A C relay circuit fault P1654 W 3 1 Lat 1999 2nd gear start lamp circuit N 3 4 1999 2000 C F G H W 3 8 Reduced engine power lamp circuit Table 8 2 Truck DTCs with multiple definitions sheet 1 of 2 DTCs with Multiple Definitions Trucks DTC YEAR 5th VIN ENGINE DEFINITION P1641 2000 P 6 5 MIL control circuit fault P1642 1996 U 3 4 Air pump relay P1643 1997 2001 All 6 5 Wait to start circuit 1996 U 3 4 Fan relay 2 circuit fault P1652 Others Vehic
2. Some GM vehicles transmit slightly different data lists for different test functions For example certain models transmit a data list during some functional tests that is shorter than the data list transmitted in diagnostic mode Some models do not transmit codes during a road test However many GM vehicles transmit the same data under all conditions 139 140 Testing Control Systems Tests Except ABS On OBD II vehicles the scan tool displays the data parameters in as many as five separate data lists Whether a vehicle transmits an identical data list or variable data lists for different test conditions affects some settings on the scan tool e Fix display lines or reassign LED functions for an ECM that always transmits the same data list and those settings stay in the scan tool memory until they are changed or a new vehicle ID is entered e Fix display lines or reassign LED functions for a vehicle that transmits variable data lists and those settings return to their preassigned functions when test selections are changed when changing from Road Test to Diagnostic Testing mode for example See the user s manual for the diagnostic tool you are using for instructions on reassigning LED functions Diagnostic Trouble Codes On some vehicles diagnostic trouble code DTC information appears as part of the data list Figure 8 7 RPM_ 1234 O2 mV __689 INTEGRATR_ 128 ROAD TEST MODE OK TO DRIVE 13 O2 SENSOR NOT WARM ENOUG
3. no communication message displays Figure 8 22 NO COMMUNICATION MAY NOT BE ATC EQUIPPED VEHICLES WITH ATC HAVE AUTO 4WD SWITCH ON DASH PRESS Y TO RETURN TO CODES amp DATA MENU Figure 8 22 Sample ATC no communication message Codes Airbag Some older models display DTCs for the supplemental inflatable restraint SIR or airbag system However the airbag control module does not display data parameters Therefore CODES is the only selection available on the MAIN MENU GM AIRBAG Figure 8 23 MAIN MENU GM AIRBAG gt CODES OTHER SYSTEMS CUSTOM SETUP Figure 8 23 Sample early pre 1994 airbag main menu Selecting CODES displays the airbag codes Figure 8 24 AIRBAG CODES DIAGNOSTIC MODE DO NOT DRIVE 71 DEFECTIVE DERM HC HISTORY CODES FOLLOW Figure 8 24 Sample early pre 1994 airbag code display Any codes currently present display toward the top of the code list When a current code is set it gets added to the list of history codes See Codes amp Data Selections on page 139 for 1994 and later models and for 1993 and later Saturn airbag testing 8 1 4 Functional Tests 1995 and Earlier NOTE Operations described in this section are not available on all tool platforms All functional tests for 1995 and earlier models are described below Not all tests are available for every model only those tests available from each specific test vehicle display Following is a complete li
4. e The ignition switch must be on When ABS CODES amp DATA is selected the scan tool first displays a waiting for communication message Figure 8 52 WAITING FOR MODULE TO COMMUNICATE WITH SCANNER CONNECT ALDL CONNECTOR Figure 8 52 Sample waiting for communication message After about 3 seconds waiting for brake module to respond should appear on the fourth line of the display Then a time counter appears at the end of the fourth line to count seconds as the scan tool establishes communication with the EBCM The time required to establish communication depends on the EBCM not on the scan tool Communication can take up to 45 seconds on some systems When the scan tool establishes communication the ABS Codes amp Data display appears If communication is not established or if communication is interrupted during testing a communication lost message displays Figure 8 53 This might happen if the ALDL 161 162 Testing ABS Systems connector is loosened or the ignition is switched off If so press N to check the vehicle ID If the ID is correct check the vehicle connector for damaged terminals and open wiring COMMUNICATION WITH BRAKE MODULE LOST TO ESTABLISH CYCLE KEY OFF 5 SEC THEN PRESS Y TO CONTINUE OR PRESS N TO REIDENTIFY SYSTEM Figure 8 53 Sample communication lost message This message means the scan tool is not receiving data from the EBCM In some cases the message may indicate an
5. Figure 8 15 Sample DTC display when Freeze Frame Failure Records is selected A DTC followed by FREEZE FRAME indicates an emissions related DTC that meets OBD II freeze frame requirements A DTC not followed by FREEZE FRAME indicates that the DTC is either non emissions related or is emissions related but has not yet met the OBD II freeze frame requirements The GM failure records may include more data than OBD II freeze frames The scan tool displays both a freeze frame and a failure record selection for emissions related DTCs Selecting FREEZE FRAME FAILURE RECORD displays a please wait message while the data is loading then the freeze frame and failure record displays Figure 8 16 FREEZE FRAME FAILURE RECORD DATA CODES amp DATA OK TO DRIVE P0201 CYLINDER 1 INJECTOR CKT PROBLEM ENGINE LOAD 3 O COOLANT C 100 Figure 8 16 Sample freeze frame and failure record display History The HISTORY selection displays any history DTCs that are stored in PCM memory since the last time DTCs were cleared Figure 8 17 CODE LIST CODES amp DATA OK TO DRIVE P0122 TP SENSOR OR APP SENSOR 1 CKT SHRT END OF LIST Figure 8 17 Sample history display when codes are present MIL SVS or Message Requested The MIL SVS OR MESSAGE REQUESTED selection displays DTCs that are currently turning on the MIL SVS lamp or displaying a message on the message console Last Test Failed The LAST TEST FAILED se
6. Press Y to enter the test A data list similar to that for Codes amp Data displays Figure 8 51 ON1 RPM 850 O2 mV __689 INT 128 EGR TEST DO NOT DRIVE APP 3 02 APP AVG 04 O02 SENSOR B1 05 02 SENSOR B2 Figure 8 51 Sample digital EGR control test data with solenoid one active When the test begins solenoid 1 cycles at regular intervals The value in the upper left corner of the display changes between OFF and ON1 to indicate the status of solenoid one Figure 8 51 ON indicates the solenoid is energized to open the first valve orifice Engine speed should drop as the EGR valve opens in response to solenoid one 3 Press Y to test the each following solenoid in succession Linear EGR Valve A linear EGR valve is a single orifice valve with variable opening controlled by a stepper motor The PCM controls the valve opening in 10 increments by commanding the stepper motor position A variable control test routine is used to test a linear EGR valve See Variable Control Test on page 158 for testing information 8 1 6 Clear Codes Most GM vehicles allow clearing DTC records from the selected ECM memory through the scan tool When available CLEAR CODES can appear on the Codes menu or on the Exit menu If the option is not available the choice does not appear on the menu If code clearing was successful a no codes present message appears If code clearing fails for any reason previous codes reappear when t
7. The scan tool does not display data during this test This is a timed test that automatically ends after 120 seconds to avoid catalytic converter overheating Fixed 10 Spark The FIXED 10 SPARK selection on the Functional Tests menu is available on 1985 and later Cadillac C body models with a 4 1L engine In this test mode the PCM sets a fixed 10 of spark advance which is the base timing setting and disables EGR The following conditions must be met for the PCM to maintain 10 of spark advance during this test e Engine temperature must be above 85 C 185 F e Engine speed must be under 900 RPM e The transmission must be in park Selecting FIXED 10 SPARK displays the Fixed Spark screen Figure 8 38 Follow instructions on the vehicle emission control information VECI decal to adjust timing 10 RPM 1234 0O2 mv 689 INT x FIXED SPARK DO NOT DRIVE Figure 8 38 Sample Cadillac fixed 10 spark screen When this test is active the standard data list displays and 10 appears at the top left to indicate the system is in the Fixed 10 Spark mode and the vehicle should not be driven 8 1 5 Functional Tests 1996 and Later NOTE i Operations described in this section are not available on all tool platforms Beginning with the 1996 model year interactive bidirectional functional tests were added to OBD II vehicles Because there are more than 250 of these tests it is not practical to describe them all However t
8. currently present hard code In the example no other codes have set An intermittent problem that occurs before other codes may display as the last code set This is the case if no other codes occurred since it set 8 2 6 VCM 4WAL Codes amp Data 1994 97 The 1994 97 Kelsey Hayes Vehicle Control Module VCM 4 Wheel Antilock Brake 4WAL system integrates ABS with the engine controls in the VCM on some vehicles This system has a red brake lamp and an amber antilock lamp on the instrument panel When the ignition is turned on both lamps light for about 2 seconds The antilock lamp goes out if there are no ABS faults If there is a fault the lamp stays lit or it lights when the fault occurs The Codes amp Data display for the VCM 4WAL brake system used on 1994 and later trucks and vans is shown in Figure 8 61 ABS LAMP ON BRAKE SW OPEN ABS BRAKING IS OFF OK TO DRIVE NO CODES PRESENT LF WHEEL 60 RE WHEEL 60 Figure 8 61 Sample Kelsey Hayes VCM 4WAL Codes amp Data 8 2 7 4WAL Codes amp Data 1990 and Later The Codes amp Data display for the Kelsey Hayes Four Wheel Antilock 4WAL brake system used on 1990 and later trucks and vans is shown in Figure 8 62 ABS LAMP LF WHEEL LR WHEEL BRAKE LAMP CMD Figure 8 62 Sample Kelsey Hayes 4WAL Codes amp Data Kelsey Hayes 4WAL has both a red brake indicator lamp and an amber antilock indicator lamp on the instrument panel When the ignition is turned o
9. left indicates the system is in the Full Rich FR Mixture mode e The VOTE parameter which indicates a rich or lean exhaust condition should be a positive high number in full rich mode e The MC dwell reading should remain fixed at 6 The data list is the same list seen in the Codes amp Data mode The vehicle should not be driven while the test is active Line 1 is fixed and displays the RPM VOTE and MC dwell If N is not pressed within two minutes of starting the test the display automatically returns to the Functional Tests menu 153 154 Testing Control Systems Tests Except ABS Backup Fuel The BACKUP FUEL selection on the Functional Tests menu lets you check the operation of the backup fuel program of the PCM on some fuel injected vehicles The backup fuel program is a fail safe or limp in program that sets a fixed injector pulse width This allows the vehicle to be driven to a shop for repair in case of a major system failure The backup fuel test verifies that the PCM backup program is operational but may also be used for checking the operation of the fuel injection system If a vehicle with a driveability problem seems to run better in Backup Fuel mode than in normal operation fuel metering and air intake parameters should be checked carefully Selecting BACKUP FUEL displays the Backup Fuel Active screen Figure 8 36 No data is available during this test The scan tool ends the test automatically after 120 se
10. on the scan tool display Figure 8 44 157 158 Testing Control Systems Tests Except ABS FUEL PUMP RELAY ON OFF ON OFF CHANGE DATA PRESS N TO EXIT RPM 850 TPS V 1 25 TPS 3 23 ADAPT SHIFT CNT_ OFF Figure 8 44 Sample Fuel Pump Relay Functional Test Variable Control Test Figure 8 45 is an example of a typical variable control test CANISTER PURGE gt TEST SCROLL DATA CHANGE LIST EXIT RPM 630 TPS 0 EVAP PURGE ____ 30 EVAP VENT SOL OFF Figure 8 45 Typical Canister Purge functional test screen Selecting TEST from this screen changes the display to show the commanded duty cycle of the Canister Purge solenoid as a percentage starting with zero Figure 8 46 CANISTER PURGE 0 lt SCROLL DATA CHANGE LIST EXIT RPM 630 TPS 0 EVAP PURGE 3 0 EVAP VENT SOL OFF Figure 8 46 Typical Canister Purge functional test screen NOTE Some variable control tests such as command gear require a press of the Y button to confirm each variable value change request During a variable control test scroll to increase or decrease the variable control value In the above example scrolling instantaneously changes Canister Purge solenoid opening by varying the duty cycle in increments of 10 The duty cycle commanded by the scan tool also appears in the upper right corner of the screen Figure 8 47 Other variable control tests act similarly CANISTER PURGE 3 gt 10 10 lt SCR
11. rear outlet valve circuit fault C1252 Sod E ICCS2 data link left fault W N If ABS channel in release too long 2000 01 K Left front normal force circuit fault 2001 W If ABS channel in release too long Table 8 3 Passenger car DTCs with multiple definitions sheet 2 of 2 DTCs with Multiple Definitions Cars DTC YEAR 4th VIN 5th VIN DEFINITION E K ICCS2 data link right fault 1998 99 W J N U X RF ABS channel in release too long E ICCS2 data link right fault C1253 2000 W N RF ABS channel in release too long 2000 01 K RF normal force circuit fault 2001 WwW RF ABS channel in release too long 1997 H Stabilitrac active handling sensors uncorrelated 1997 All others RF solenoid circuit shorted to battery re 1997 99 Y Steering sensors uncorrelated G Brake thermal model exceeded 4998 99 W N J U X RF solenoid circuit shorted to battery Stabilitrac active handling sensors E K uncorrelated E Stabilitrac active handling sensors uncorrelated 2000 AE W N RF solenoid circuit shorted to battery a H C K Steering sensors uncorrelated WwW RF solenoid circuit shorted to battery 2001 H G Y E K V c Steering sensors uncorrelated Clearing Codes from ABS Codes amp Data The CLEAR ABS CODES selection appears on a menu only if the scan tool is able to clear codes from the system being tested After repairs are made clear the codes
12. selection screen 2 Select a data list option After a short pause the first two lines of the new data display Review the selected list to make sure the desired parameters are displayed Press Y to exit the data list and return to the functional test Data parameter selections may be changed during a test Functional Test Operation Functional test operation varies depending on the test There are four general types of functional test operation e Information Tests These are read only types of tests For instance select VIN from the functional tests and the scan tool displays the VIN number e Toggle Tests These tests switch a component such as a solenoid relay or switch between two operating states The terms on off open clsd open closed enab disa enable disable excd norm exceeded normal pass fail lean rich high norm or rev fwd reverse forward may be used to name states e Variable Control Tests These tests command a certain value for a system or component For instance the delta spark retard test allows the scan tool to vary spark timing in one degree increments up to ten degrees Similarly the EGR test allows varying the EGR valve duty cycle from zero to 100 percent e Reset Tests These tests reset the adaptive or learned values stored in the PCM 6 0 6 The toggle tests variable control tests and reset tests all look very similar
13. the lamps may stay lit and the disabled messages may appear for up to 30 seconds The antilock lamp should go out after no more than 30 seconds if there are no ABS faults present If an ABS fault is present the antilock lamp stays lit or it lights when an ABS fault occurs The brake lamp stays on if the parking brake is applied or if a basic hydraulic brake problem such as low brake fluid level exists In normal operation the antilock lamp should be off when no faults are present It should light continuously whenever a fault is present The EBCM EBTCM recognizes both current or 171 172 Testing ABS Systems hard and intermittent or soft faults The EBCM EBTCM stores codes in memory for intermittent problems Reading Teves II ABS Codes The DISPLAY ABS CODES selection on the scan tool causes the antilock lamp to flash codes The lamp flashes up to seven codes that are currently present or stored in memory However the lamp flashes only one code at a time To proceed to the next code exit and then reenter the display ABS codes selection If the antilock lamp is off before entering Display ABS Codes any code that displays indicates an intermittent or soft fault If the antilock lamp is on before entering Display ABS Codes one or more displayed ABS codes indicate a current or hard fault If two or more codes are present there is no way to distinguish hard codes from soft codes To read the codes 1 Switch the ignition
14. ABS problem However other causes are more common ABS Codes amp Data Communication Guidelines To ensure efficient communication with the EBCM follow these steps Be sure the ignition is switched off when entering the vehicle ID Switch the ignition on before selecting CODES amp DATA Switch the ignition off when ABS Codes amp Data testing is complete To test the engine control system leave the ignition off while changing the ALDL test adapters then enter the vehicle ID for engine testing m Fault Codes Diagnostic trouble codes DTCs may be hard codes indicating a problem is continuous or soft codes indicating a problem that occurred in the past but is not present now See Hard Codes and Soft Codes on page 140 for a complete explanation Diagnostic Trouble Codes with Multiple Definitions A few 1996 and later GM vehicles output OBD II style DTCs that have varying definitions The correct DTC definition cannot be determined by the VIN characters entered during the vehicle identification sequence In these instances the display shows the DTC followed by a message that refers you to this manual Use Table 8 1 to determine the DTC definition Table 8 3 Passenger car DTCs with multiple definitions sheet 1 of 2 DTCs with Multiple Definitions Cars DTC YEAR 4th VIN 5th VIN DEFINITION E K ICCS2 data link left fault 1998 99 W J N U X If ABS channel in release too long G Right
15. GM Testing This chapter provides information and procedures for using the scan tool with the following control systems e Engine e Transmission e Airbag e Antilock Brake System ABS For additional information on GM vehicles see the following sections e GM Operations on page 121 e GM Data Parameters on page 435 e GM Communications Problems on page 731 8 1 Testing Control Systems Tests Except ABS Select ENGINE AND OTHER SYSTEMS from the System Selection menu to open the main testing menu for all GM systems except ABS Figure 8 1 MAIN MENU GM ENGINE OTHER SYSTEMS gt CODES amp DATA AND ROAD TEST FUNCTIONAL TESTS TROUBLESHOOTER CUSTOM SETUP Figure 8 1 Sample GM main menu for all systems except ABS To test GM vehicles the scan tool must communicate with the vehicle electronic control module ECM and receive data over a serial data link It does this through the ALDL connector Serial means data parameters are transmitted one after the other in series The scan tool operates at a speed that depends on the length of the serial data stream and on the baud rate of the vehicle ECM Baud rate is the data transmission speed in digital bits per second Typical GM engine baud rates are 80 for minimum function systems 160 for carbureted and early fuel injected systems 8192 for 1988 95 port fuel injected engines and 10 400 10 4K for 1996 and later fuel injected engines The baud rate determines
16. H 15 COOLANT TEMP SIGNAL HIGH OR OPEN Figure 8 7 Sample codes present screen Most body control module BCM trouble codes include an alpha prefix These BCM codes display alphanumerically Hard Codes and Soft Codes On some 1995 and earlier models DTCs may be classified as either hard or soft Most 1988 and later GM vehicle controllers separate soft codes from hard codes e Hard codes indicate a problem that exists at the time of testing These are referred to as current codes in the trouble code menu e Soft codes indicate a problem that occurred in the past but is not present now These are referred to as history codes in the trouble code menu To distinguish between hard and soft codes 1 Clear the ECM memory and reenter Codes amp Data 2 Watch for codes to reappear A hard code reappears quickly from immediately to a couple of minutes A soft code does not reappear until the problem that caused it reoccurs 1995 and Earlier Cadillac Engine System Codes Cadillac systems transmit hard codes for the engine However soft codes are available only from the Cadillac on board diagnostic system with the following exceptions e 1989 and earlier models transmit a soft code 52 e 1990 95 models transmit soft codes 52 and 109 Refer to Cadillac service procedures or the Fast Track Troubleshooter Reference G074 for instructions on using the Cadillac system Diagnostic Trouble Codes Without Def
17. NU gt CODES amp DATA AND ROAD TEST SPARK DATA CODES HISTORY ENGINE DATA 1 FUEL TRIM DATA Figure 8 14 Sample Codes amp Data menu submenu Menu choices vary depending on the vehicle As with other menus only the items available for the specific test vehicle display Codes amp Data menu choices may include e Adaptive Report e Codes e Codes amp Data and Road Test e Code History e EGR EVAP ACC e EGR and Misfire Data e Engine Data e Fuel Trim Data e Idle and Cruise Data e Misfire Data e Spark Data Codes On OBD II vehicles selecting CODES from the CODES amp DATA MENU opens a submenu that may include the following options e Freeze Frame Failure Records e History e MIL SVS or Message Requested e Last Test Failed e Test Failed Since Code Cleared e Failed This Ignition e DTC Status e Automatic Transfer Case ATC Codes Some OBD II vehicles offer an ALL POWERTRAIN CODES option Selecting ALL POWERTRAIN CODES displays any DTC stored in the PCM Freeze Frame Failure Records Selecting FREEZE FRAME FAILURE RECORDS displays freeze frame and failure records associated with a particular DTC These records include stored values of selected data parameters at the time a DTC sets Selecting this mode displays a list of all DTCs in PCM memory Figure 8 15 145 146 Testing Control Systems Tests Except ABS CHOOSE A FAILURE RECORD OR FREEZE FRAME gt P1406 FREEZE FRAME P1406 P1577
18. OLL DATA CHANGE LIST EXIT RPM 630 TPS 0 EVAP PURGE 3 10 EVAP VENT SOL OFF Figure 8 47 Typical Canister Purge functional test screen EGR Control NOTE Since a proper Exhaust Gas Recirculation EGR system operation is crucial to preventing a vehicle from emitting high levels of NOx the EGR control test is described in detail here This bidirectional functional test is available on some 1996 and later engines In this mode the scan tool commands the PCM to cycle the EGR valve The EGR valve opens and closes at fixed intervals to provide a functional test of EGR system operation Tests vary slightly for each of the following three types of EGR valve e Integrated electronic EGR valve e Digital EGR valve e Linear EGR valve Some engines that use these EGR valves do not have a PCM with the communication ability required to perform the functional test The EGR control test selection only appears on the Functional Tests menu for those vehicles with the necessary capability The scan tool displays the standard Codes amp Data list during the EGR control tests However there are slight differences These differences are explained below Integrated Electronic EGR Valve An integrated electronic EGR valve has a built in solenoid controlled by the PCM The solenoid opens and closes a vacuum vent for the valve When the vacuum vent is opened The EGR valve is closed When the vacuum vent is closed The EGR valve opens Select
19. R ARE SELF CALIBRATING IN WHICH CASE AN ALLOWABLE SERVICE RANGE IS GIVEN PRESS Y TO CONTINUE N TO EXIT Figure 8 30 Second screen of the caution message 3 Press Y to enter the test Depending on engine calibration one of three possible TPS test screens displays Figure 8 31 Figure 8 32 or Figure 8 33 CURRENT TPS V 0 58 ADJUSTMENT SPEC V 0 55 0 05 ALLOWABLE RANGE V 0 35 TO 0 67 NO ACTION REQUIRED IF WITHIN RANGE Figure 8 31 Sample screen when the TPS can be adjusted CURRENT TPS V 0 58 ADJUSTMENT SPEC V NOT ADJUSTABLE ALLOWABLE RANGE V 0 45 TO 1 25 NO ACTION REQUIRED IF WITHIN RANGE Figure 8 32 Sample screen when the TPS is not adjustable TPS MUST BE SET AT SENSOR BECAUSE ECM REPORTS ANGLE NOT VOLTAGE WITH ENGINE OFF amp ISC RETRACTED SET TPS TO READ 10 OF REFERENCE VALUE AT SENSOR Figure 8 33 Sample screen when TPS angle not voltage is reported Full Lean FL Mixture The FULL LEAN FL MIXTURE selection on the Functional Tests menu is available only for a minimum function system which is used on carbureted T body models e Chevette e Acadian e T 1000 In this mode the PCM commands the MC solenoid to a fixed 54 dwell or 90 duty cycle condition Figure 8 34 This mode is used to check O2S operation and other engine operating conditions while the fuel system is held in a full lean condition FL RPM_1234 VOTE 54 MC DWL 54 FULL LEAN TEST DO NO
20. ST MODE OK TO DRIVE ECM REMOVED FROM DIAGNOSTIC MODE NO CODES OR DATA AVAILABLE PRESS N FOR MAIN MENU Figure 8 10 Sample ROAD TEST NO C amp D screen Codes amp Data and Road Test Many 1986 and later GM vehicles provide only the Road Test mode or open mode for viewing the engine and transmission data For these vehicles CODES amp DATA AND ROAD TEST displays on the MAIN MENU GM ENGINE Figure 8 11 MAIN MENU GM ENGINE OTHER SYSTEMS gt CODES amp DATA AND ROAD TEST lt FUNCTIONAL TESTS REVIEW MOVIE CUSTOM SETUP Figure 8 11 CODES amp DATA AND ROAD TEST selection This mode may be used for testing in the shop as well as for road testing Select this function and the second line of the display shows the vehicle may be driven Figure 8 12 RPM_ 1234 O2 mV __689 INTEGRATR_ 128 CODES AND DATA OK TO DRIVE NO CODES PRESENT O2 SENSOR B1 05 02 SENSOR B2 06 Figure 8 12 Sample Codes and Data and Road Test display Codes amp Data Menu Some vehicles have a CODES amp DATA MENU selection Figure 8 13 which is used to access data from various data groups MAIN MENU GM ENGINE OTHER SYSTEMS gt CODES amp DATA MENU lt FUNCTIONAL TESTS CUSTOM SETUP TROUBLESHOOTER Figure 8 13 CODES amp DATA MENU selection 144 A data group combines similar data parameters into smaller data lists for faster more efficient testing Figure 8 14 CODES amp DATA ME
21. T DRIVE Figure 8 34 Sample full lean FL mixture test During the full lean FL mixture test the standard diagnostic data list for a minimum function system displays e FL appears at the top left to indicate the system is in the Full Lean FL Mixture mode e The VOTE parameter which indicates a rich or lean exhaust should be negative during full lean operation e The MC dwell reading should remain fixed at 54 The data list is the same list seen in the Codes amp Data mode The vehicle should not be driven while the test is active Line 1 is fixed and displays the RPM VOTE and MC dwell If N is not pressed within two minutes of starting the test the display automatically returns to the Functional Tests menu Full Rich FR Mixture The FULL RICH FR MIXTURE selection on the Functional Tests menu is available only for a minimum function system which is used on carbureted T body models e Chevette e Acadian e T 1000 In this mode the PCM commands the MC solenoid to a fixed 6 dwell or 10 duty cycle condition Figure 8 35 Use this mode to check O2S operation and other engine operating conditions while the fuel system is held in a full rich condition FR RPM_1234 VOTE 54 MC DWL 54 FULL RICH TEST DO NOT DRIVE Figure 8 35 Sample full rich FR mixture test During the full rich FR mixture test the standard diagnostic data list for a minimum function system displays e FR at the top
22. TURN KEY ON Figure 8 2 Sample waiting for module to communicate message If communication is not established within five seconds the screen updates to display a no communication message Figure 8 3 NO COMMUNICATION IS KEY ON IS ALDL CONNECTED WAIT 15 SECONDS PRESS N TO REENTER VEHICLE IDENTIFICATION OR SEE REFERENCE MANUAL APPENDIX B Figure 8 3 Sample no communication message This message stays on the screen until communication is established then the scan tool displays the selected function If communication is established but it does not match what the scan tool is looking for a communication mismatch message displays Figure 8 4 COMMUNICATION MISMATCH PRESS N TO REENTER VEHICLE ID OR PRESS Y TO CONTINUE Figure 8 4 Sample communication mismatch message This generally occurs if the vehicle is improperly identified or if the selected module has the wrong PROM installed It may also be due to undocumented midyear changes 138 8 1 3 Codes amp Data Selections The Codes amp Data selections for different vehicles vary but each one with or without road test opens a data display screen that presents DTCs and onboard computer data The Codes amp Data test selections are e CODES amp DATA displays trouble codes and data stream information from the selected ECM The vehicle should not be driven during this test e ROAD TEST C amp D allows the vehicle to be driven whi
23. and return to the previous ABS Codes amp Data display If the faults are repaired the display indicates no codes present If the code clearing operation fails for any reason previous codes reappear in the ABS Codes amp Data display Press N to return to the exit menu and repeat the clear ABS codes operation 8 2 2 Bosch 2 Codes amp Data 1990 97 An ABS Codes amp Data mode is available for 1990 and later Bosch 2 systems In this diagnostic mode the antilock functions of the Bosch 2 system are disabled by the EBCM and new trouble codes cannot be set However the service brakes operate normally and the vehicle can be driven safely for testing In ABS Codes amp Data mode Figure 8 54 the top line of the display is fixed and displays the EBCM part number and the current position of the brake light switch followed by the test mode and the ABS Codes amp Data list 163 164 Testing ABS Systems ECU BB 33599 BRAKE LIGHT SW ON ABS BRAKING IS OFF OK TO DRIVE NO CODES PRESENT LF WHEEL MPH 45 RF WHEEL MPH 45 Figure 8 54 Sample Bosch 2 Codes amp Data Select CODES amp DATA on a Bosch 2 system and the EBCM enters a diagnostic state The EBCM remains in the diagnostic state after exiting Codes amp Data The ABS is disabled until the ignition is switched off To restore the ABS to normal operation 1 Switch the ignition off 2 Disconnect the scan tool The Bosch 2 EBCM enters the diagnostic
24. brake light switch and the state of the ABS warning lamp when in the Codes amp Data mode followed by the test mode and the codes amp data list Figure 8 58 BRAKE SW OPEN ABS LAMP OFF ABS BRAKING IS OFF OK TO DRIVE NO CURRENT CODES PRESENT LF WHEEL MPH 45 RF WHEEL MPH 45 Figure 8 58 Sample Delco Moraine III Codes amp Data NOTE Vehicle components may seem to operate abnormally during testing in Codes amp Data mode A digital instrument panel may appear to stop working or analog gauge readings may change randomly This is normal and stops once the EBCM is out of the diagnostic state Delco Moraine III Trouble Codes The scan tool only displays codes for faults present at the time of testing for Delco Moraine III systems These are generally referred to as hard or current codes The system does not display soft or history codes When there are codes or if a new code occurs during testing the third line changes to display the code Figure 8 59 BRAKE SW OPEN ABS LAMP OFF ABS BRAKING IS OFF OK TO DRIVE 14 REAR RELEASE SOL OPEN OR SHORT TO GND LF WHEEL MPH 45 RF WHEEL MPH 45 Figure 8 59 Sample Delco Moraine III display with codes If no ABS problems occur within 50 ignition cycles the EBCM clears any codes stored in its memory The scan tool cannot be used to clear codes from the Delco Moraine III system Capturing Intermittent Faults The EBCM only displays intermittent faults tha
25. conds as a bulb check when the ignition is first switched on If there are no ABS faults present the lamp turns off while the engine is cranking If an ABS fault is present the lamp stays lit during cranking When an ABS fault occurs while driving the ABS lamp lights The brake lamp lights only in the presence of a hydraulic failure or when the parking brake is applied DBC 7 Main Menu Options The DBC 7 system offers several main menu options for displaying information The following menu choices are available e Codes amp Data e Codes e Data only In Codes amp Data mode any codes stored in memory display followed by a data list of ABS parameters In Codes mode a list of any codes in memory displays Figure 8 66 Data parameters do not display CODE LIST CODES amp DATA OK TO DRIVE C0221 RF WHEEL SPEED SENSOR CKT OPEN END OF LIST Figure 8 66 Sample DBC 7 codes Similarly in Data Only mode the screen displays data parameters only Figure 8 67 Codes do not display in this Data Only mode IGN V 12 4 VEH SPEED DATA ONLY OK TO DRIVE NO CODES AVAILABLE IN THIS MODE LF WHEEL 10 LR WHEEL Figure 8 67 Sample DBC 7 data only 8 2 13 Display ABS Codes RWAL amp Teves Il The DISPLAY ABS CODES selection on the MAIN MENU GM ABS provides a way to read codes flashed on the ABS warning lamp for these systems that cannot communicate with the scan tool After reading the codes enter the co
26. conds to avoid catalytic converter overheating and returns to the Functional Tests menu BACKUP SPARK amp FUEL ACTIVE 120 SECONDS ECM IS OPERATING IN LIMP HOME MODE NO DATA AVAILABLE TEST WILL END IN 2 MINUTES OR PRESS N TO EXIT Figure 8 36 Sample backup spark and fuel screen The backup fuel test for 1982 85 Cadillac models with onboard diagnostics is slightly different Press and hold INST AVG on the fuel panel to activate Figure 8 37 BACKUP FUEL TEST ENABLED ACTIVATE BY HOLDING INST AVG KEY ON FUEL PANEL NO DATA AVAILABLE AUTOMATIC EXIT AFTER 2 MINUTES PRESS N TO EXIT SOONER Figure 8 37 Sample active backup fuel test screen Backup Spark amp Fuel The BACKUP SPARK AND FUEL selection on the Functional Tests menu checks operation of the PCM backup spark and fuel program on some fuel injected vehicles Backup spark and fuel is a fail safe or limp in program that sets base timing and a fixed fuel injector pulse width This allows the vehicle to be driven in case of a major system failure This test verifies that the PCM backup program is operational but may also be used to double check the operation of the fuel injection system If a vehicle with a driveability problem seems to run better in Backup Spark and Fuel mode than in normal operation check fuel metering ignition and air intake parameters carefully Selecting BACKUP SPARK AND FUEL displays the Backup Spark and Fuel screen Figure 8 36
27. connector does not clear Teves II ABS codes from the EBCM EBTCM After repairs clear codes by driving at a speed above 18 MPH 29 KPH Then repeat the code reading sequence to make sure that all ABS problems were corrected 8 2 11 Teves IV ABS Codes amp Data 1990 99 The ABS Codes amp Data display for Teves IV systems provides trouble code information only data parameters are not displayed Figure 8 65 TEVES IV ABS BRAKING IS OFF OK TO DRIVE 23 RF WHEEL SPEED IS 0 MPH END OF LIST Figure 8 65 Sample Teves IV ABS Codes amp Data In the ABS Codes amp Data mode the antilock functions of the Teves IV system are disabled by the EBCM Be aware new codes cannot be set in this mode even if fault conditions are present The service brakes operate normally and the vehicle can be driven safely for testing When you select ABS CODES amp DATA for the Teves IV system the scan tool establishes communication with the EBCM and puts the module in a diagnostic state During ABS Codes amp Data testing the amber ABS lamp on the instrument panel flashes once per second The EBCM returns to normal operation once N is pressed to exit ABS Codes amp Data Unlike Bosch systems the ignition does not need to be cycled or the scan tool disconnected to restore ABS functions With Teves IV ABS testing may cause false ECM codes to appear on the engine code list After ABS testing reenter the vehicle ID for engine testing and ch
28. des into the scan tool to get a code description and to record the codes for reference or printing The Display ABS Codes function provides easy and quick access to code definitions faster than looking them up in a service manual If troubleshooter tips are available for the system being tested DISPLAY ABS CODES fills in the code summary line that appears at the top of the troubleshooter menu Before using the Display ABS Codes function be sure to read the Read This First instructions on the scan tool if working with a specific GM antilock brake system for the first time or if it is a system worked on infrequently See Read This First Instructions on page 179 for details When Pin H of the ALDL is grounded the indicator lamp on the instrument panel flashes codes Codes display differently for RWAL and Teves II systems How codes display is explained for each specific system How each system indicates normal operation or no faults present is also explained P To display ABS codes 1 Switch the ignition on 2 When instructed select DISPLAY ABS CODES Pressing the Y button here causes the scan tool to ground the ABS diagnostic terminal Pin H of the ALDL connector and displays a code summary screen Figure 8 68 CODE SUMMARY NO CODES ENTERED YET BRAKE LIGHT FLASHES CODES IF IGNITION ON SCROLL amp PRESS Y TO MARK OR UNMARK CODES 12 OPEN LEFT FRONT WHEEL SENSOR Figure 8 68 Sample code summary 3 Select t
29. eck for engine codes Clear any codes that may be present and recheck to be sure they were false If no codes are present in the system a no codes present message displays on the third line New codes cannot be set because the system is in diagnostic mode If codes are present the third line displays the code number and title 8 2 12 Delphi Brake Controller 7 DBC 7 Codes amp Data 1999 2004 The DBC 7 brake system is used on some 1999 2004 models This system does not flash codes on an instrument panel lamp Codes must be read on the scan tool display The DBC 7 system has a red brake indicator lamp and an amber ABS warning lamp on the instrument panel The DBC 7 system does not light the brake lamp It is only lit by the base braking system The DBC 7 electronic control module monitors various brake inputs to determine whether to prepare for antilock braking The ABS and traction control operations are combined in a single control unit the Electronic Brake Traction Control Module EBTCM on DBC 7 systems During ABS braking the EBTCM operates the Electronic Brake Pressure Modulator Valve BPMV assembly based on the comparison of data parameter values to the programmed values stored in memory The EBCM EBTCM also monitors system related conditions and takes corrective diagnostic action when necessary 173 174 Testing ABS Systems ABS Warning Lamp Operation Under normal conditions the ABS lamp lights for several se
30. he code flashed by the ABS lamp An asterisk appears on the code line and the code number appears in the code summary on the top line Figure 8 69 Pressing Y again deselects a selected code CODE SUMMARY 14 12 OPEN LEFT FRONT WHEEL SENSOR 14 OPEN RIGHT FRONT WHEEL SENSOR 16 OPEN LEFT REAR WHEEL SENSOR Figure 8 69 Code summary screen with a code selected 4 Continue through the code list and enter all codes flashed by the ABS lamp 5 Press N to exit the code summary display and return to the code list The code list contains all codes possible for the system being tested Enter and exit the Display ABS Codes mode to mark or unmark codes as often as necessary when diagnosing a specific system The selected codes are stored in scan tool memory until the list is changed or until a new vehicle or system ID is entered Clearing Codes From Display ABS Codes When available the clear ABS codes selection for display ABS codes erases the records from the ABS module memory It does not clear code selections from code summary line of the display ABS codes screen After the display returns to ABS codes mode manually unmark code selections as explained in earlier in this chapter 175 Testing ABS Systems 8 2 14 Functional Tests Delco Moraine Ill Brake Bleeding NOTE i Operations described in this section are not available on all tool platforms A FUNCTIONAL TESTS selection is available for bleeding the Powermaster III electr
31. he display returns to the Data Viewing mode In this case repeat the code clearing procedure 160 8 2 Testing ABS Systems Four wheel antilock brake systems 4WAL are available on most 1986 and later GM cars and trucks and rear wheel antilock RWAL brake systems are available on 1988 95 2 wheel drive light trucks On most 1988 and later systems the antilock brake system ABS electronic brake control module electronic brake traction control module EBCM EBTCM lights an ABS indicator lamp on the instrument panel when a problem occurs Most systems store diagnostic trouble codes DTCs and either flash them on the warning lamp or transmit them to the scan tool Most systems also transmit serial data which is displayed by the scan tool 8 2 1 ABS Codes amp Data The ABS CODES amp DATA selection is available on the MAIN MENU GM ABS for most ABS systems This ABS selection operates similarly to that for engine testing In this mode the scan tool reads DTCs and all data available on the ABS data stream The ABS Codes amp Data displays and menus vary slightly depending on the system Communication With the ABS Module EBCM The ABS CODES amp DATA selection from the MAIN MENU GM ABS requires the scan tool to communicate with the EBCM through the ALDL connector The following conditions must be met in order to establish communication e The scan tool must be connected to power e The data cable must be connected to the ALDL
32. he test was inconclusive and must be repeated LAST TEST indicates the results of the last DTC related tests The results are either PASSED or FAILED SINCE CLEAR indicates the test status since the DTC was last cleared The results are PASSED FAILED or NOT RUN HISTORY indicates whether the PCM stored a history code The display reads YES or NO Typically a freeze frame or failure record is available fora DTC when YES displays MIL OR SVS REQ indicates the PCM command status to the malfunction indicator lamp MIL or service vehicle soon request SVS Req lamp the last time the DTC set The displays reads YES or NO YES means the PCM commanded the lamp to turn on If you enter a DTC not supported by the vehicle a message displays on screen Figure 8 20 147 148 Testing Control Systems Tests Except ABS DTC STATUS SCROLL IN DESIRED TROUBLE CODE TO TEST kkk P1976 x THIS VEHICLE DOES NOT SUPPORT THIS DTC Figure 8 20 Sample screen when a DTC is not supported Automatic Transfer Case ATC Codes The ATC CODES selection displays Automatic Transfer Case ATC DTCs Figure 8 21 The ATC is optional equipment and this menu selection does not necessarily mean the vehicle is equipped with an ATC CODE LIST CODES amp DATA OK TO DRIVE C0323 T CASE LOCK CIRCUIT LOW END OF LIST Figure 8 21 Sample ATC code list If the vehicle does not have an ATC or if there is a communication problem a
33. heating Functional Test Selection NOTE Operations described in this section are not available on all tool platforms Select FUNCTIONAL TESTS from a main menu displays one of the following menus Figure 8 40 and Figure 8 41 SELECT TEST MODE PRESS Y TO CONTINUE gt CALIBRATION P N VIN CANISTER PURGE DUTY CYCLE Figure 8 40 Sample 1996 2001 Functional Tests menu gt INJECTOR BALANCE CALIBRATION P N VIN OUTPUT CONTROLS Figure 8 41 Sample 2002 and later Functional Tests menu NOTE i Selecting OUTPUT CONTROLS displays a list of component tests Figure 8 42 SELECT TEST MODE PRESS Y TO CONTINUE gt A C RELAY ON OFF CRUISE INHIBIT ON OFF DISABLE IDLE MODE SPARK RESET Figure 8 42 Sample Output Controls menu 156 WARNING Do not enter a functional test while conducting a road test unless the road test requires it The PCM makes changes to the ignition timing fuel delivery and other vehicle functions which may affect engine operation and vehicle control Data Parameter Selection Before beginning a functional test select the data parameters to view during the test To select data parameters to view during a test 1 Select CHANGE DATA The last two lines display the data lists available for the test vehicle Figure 8 43 FUEL PUMP RELAY ON OFF gt ON OFF CHANGE DATA PRESS N TO EXIT DATA LIST 1 DATA LIST 2 DATA LIST 3 DATA LIST 4 Figure 8 43 Sample functional test data list
34. hey may be grouped into the following general categories e Adaptive memory resets e Gauge lamp and relay on off tests e Engine operating mode tests Loop Status and Cruise mode e Injector tests e Spark EGR and timing tests e Torque converter tests e Transmission shift tests e Valve and solenoid on off tests For bidirectional tests the scan tool displays a message if a device control or functional test limit is exceeded Device control limits are specific to each PCM and to each test making it impractical to list the limit criteria for all tests For 2001 and earlier vehicles a single message displays to fit all situations where a control limit is exceeded Figure 8 39 155 Testing Control Systems Tests Except ABS THE PCM EITHER TIMED OUT OR A DEVICE CONTROL LIMIT WAS EXCEEDED PRESS N TO RETURN TO FUNCTIONAL TEST MAIN MENU Figure 8 39 Exact device control limit exceeded message For 2002 and later vehicles the device control limit message is specific to the conditions at the time the test was requested If a device control limit message displays while performing a functional test it means the test aborted due to an internal function of the PCM This does not indicate a problem with the scan tool Safety limits are engineered into the PCM to prevent a functional test from enabling under inappropriate conditions such as turning off a cooling fan relay when engine coolant temperature is hot enough to cause over
35. hicle was started since the fault occurred If the fault is an intermittent problem or soft code the EBCM counts the number of starts since the code last occurred If the problem is continuous a hard code the code resets each time the necessary conditions occur The strts since code value is 0 if the code is present at the time of testing P To determine whether a fault is continuous or intermittent e Clear the code If the code reappears when the necessary conditions occur the fault is continuous The Clear Codes function appears on the ABS Codes amp Data exit menu see Clear Codes on page 160 8 2 3 Bosch and Delco Bosch 5 0 5 3 Codes amp Data 1995 2004 This section describes testing Bosch 5 0 and 5 3 ABS and Delco Bosch 5 0 and 5 3 ABS used on 1995 2004 models Selecting CODES amp DATA for these models displays a screen similar to Figure 8 56 ECU BB 33599 BRAKE LIGHT SW ON ABS BRAKING IS OFF OK TO DRIVE NO CODES PRESENT LF WHEEL MPH 45 RF WHEEL MPH 45 Figure 8 56 Sample Bosch or Delco Bosch 5 0 or 5 3 Codes amp Data During ABS tests in Codes amp Data mode other vehicle components may seem to operate abnormally The instrument panel may appear to stop working gauge readings may change randomly or LEDs may light up This is normal and stops when the EBCM is taken out of the diagnostic state Bosch and Delco Bosch 5 0 5 3 Trouble Codes Codes for these systems are viewed in
36. how quickly the scan tool responds to an ECM and how fast data readings change on the screen It also affects the length of time that it takes to record a movie Data from a high baud ECM may appear to change almost instantly Data from a low baud module appears to change much more slowly This display speed or data update rate depends on the ECM it is not controlled by the scan tool 137 Testing Control Systems Tests Except ABS 8 1 1 Bidirectional Modules Many late model GM vehicles have bidirectional ECMs This means that the ECM not only transmits data but also accepts commands from the scan tool Bidirectional ECMs transmit a complete data stream to the scan tool and provide many functional test capabilities The scan tool provides many of these bidirectional capabilities on late model GM vehicles However a few special test commands that override normal control module operation are restricted to GM test equipment See GM Communications Problems on page 731 if the scan tool cannot communicate with the vehicle 8 1 2 Scan Tool Communication The CODES amp DATA and FUNCTIONAL TESTS selections on the main menus require the scan tool to communicate with the selected ECM The ignition must be on to establish communication Select either CODES amp DATA or FUNCTIONAL TESTS and a waiting for module to communicate message displays Figure 8 2 WAITING FOR MODULE TO COMMUNICATE WITH SCANNER CONNECT ALDL CONNECTOR
37. ing EGR CONTROL from the Functional Tests menu displays the EGR Control Test screen Figure 8 48 EGR SOLENOID SHOULD CYCLE IF ENGINE IS RUNNING IDLE WILL BE SET TO 1500 RPM PRESS Y TO ENTER TEST THEN PRESS N TO EXIT Figure 8 48 Sample integrated electronic EGR control test On screen instructions guide you to the EGR Control data list While the test is active the EGR valve cycles on and off at regular intervals as indicated by OFF or ON in the upper left corner of the display Figure 8 49 OFF RPM 850 O2 mV __689 INT 128 R EGR TEST DO NOT DRIVE APP 02 APP AVG 04 02 SENSOR B1 05 02 SENSOR B2 06 Figure 8 49 Sample integrated electronic EGR control test data ON means the integral solenoid in the valve should be energized to close the vacuum vent which opens the EGR valve Engine speed should drop as the valve opens Digital EGR Valve A digital EGR valve has three solenoids that open and close different sized orifices in the valve This EGR control tests for these systems allows each of the solenoids to be operated independently 159 Testing Control Systems Tests Except ABS P To test the digital EGR valve solenoids 1 Select EGR CONTROL The EGR Control Test screen displays Figure 8 50 EGR SOLENOID SHOULD CYCLE IF ENGINE IS RUNNING IDLE WILL BE SET TO 1500 RPM PRESS Y TO ENTER TEST THEN PRESS Y FOR NEXT SOLENOID PRESS N TO EXIT Figure 8 50 Sample digital EGR control test 2
38. initions Some OBD II GM vehicles output OBD II style DTCs that have varying definitions The correct DTC definition cannot be determined by the VIN characters entered during the vehicle ID sequence In these instances the display shows the DTC followed by a message that refers you to this manual Use Table 8 1 and Table 8 2 to determine the DTC definition Table 8 1 2001 and earlier passenger car DTCs with multiple definitions sheet 1 of 2 DTCs with Multiple Definitions Cars DTC YEAR 4th VIN ENGINE DEFINITION 1996 B D Y 4 3 5 7 a Fan relay 1 circuit fault 1996 97 F 5 7 1996 99 Z 1 9 QDM A fault P1641 1996 2001 All others MIL control circuit 1998 W 3 8 All 3 8 A C relay 1999 N 3 4 A L N W 3 1 3 4 Air pump relay circuit 1996 All others Cooling fan relay 2 control circuit Y 5 7 Cooling fan relay 2 amp 3 control circuit 1996 97 F 5 7 P1642 E K 4 6 1996 99 Vehicle speed output circuit G Olds only 4 0 1997 98 All others Driver 1 line 2 1998 99 W 3 1 UO Change oil lamp circuit 1999 N 3 4 1996 B D Y 4 3 5 7 f ae Engine speed output circuit P1643 1996 97 F 5 7 1996 98 All others Fuel pump PWM circuit 141 142 Testing Control Systems Tests Except ABS Table 8 1 2001 and earlier passenger car DTCs with multiple definitions sheet 2 of 2 DTCs with Multiple Definitions Cars
39. it for the RWAL EBCM and the RWAL EBCM receives an abnormal speed signal when in the diagnostic mode Clear code 9 and any other codes See Display ABS Codes RWAL amp Teves II on page 174 for more information Clearing RWAL Codes To clear codes from the RWAL system except on vehicles that transmit ABS Codes amp Data switch the ignition off and disconnect the main connector at the RWAL EBCM Refer to Clearing Codes from ABS Codes amp Data on page 163 for information on clearing codes on vehicles with ABS Codes amp Data 8 2 9 Rear Wheel Antilock RWAL Codes amp Data Some 1993 95 The RWAL electronic control module for some 1993 95 trucks and vans monitors various brake and 4WD switch inputs to determine whether to prepare for ABS braking control The 170 RWAL EBCM operates the control valve assembly during antilock braking based on comparisons of data parameter values and programmed values stored in RWAL EBCM memory The RWAL EBCM monitors system related conditions and takes corrective action when necessary A complete Codes amp Data display for the Kelsey Hayes RWAL system used on 1993 and later S and T trucks is shown in Figure 8 64 ABS LAMP ON BRAKE SW OPEN ABS BRAKING IS OFF OK TO DRIVE NO CODES PRESENT VEH SPEED 60 VLV RESET SW 60 ISOLATION SOL OFF DUMP SOLENOID OFF ENABLE RELAY OFF INJ 2 FAULT YES EST ENABLED YES 4WD ACTIVE NO Figure 8 64 Complete Codes amp Data display f
40. le displaying trouble codes and data stream information from the selected ECM e ROAD TEST No C amp D allows the vehicle to be driven with the scan tool connected but no trouble codes or data display while driving e CODES amp DATA AND ROAD TEST displays trouble codes and data stream information from the selected ECM whether or not the vehicle is being driven e CODES displays trouble codes only no data parameters e CODES amp DATA MENU accesses a submenu of data test selections that group similar data parameters together on smaller data lists for faster more efficient testing e CODE HISTORY displays code history information e ADAPTIVE REPORT displays the adaptive or learned information that the transmission control module TCM uses to control shifting Codes amp Data Selecting CODES amp DATA displays the data list and trouble codes for the selected module Data for carbureted engines is slightly different than for fuel injected engines but both work the same Figure 8 5 and Figure 8 6 RPM_ 1234 O2 mV __689 MC DWL _ 38 DIAGNOSTIC MODE DO NOT DRIVE NO CODES PRESENT O2 CROSSCOUNTS 08 OPEN CLSD LOOP_OPEN Figure 8 5 Sample GM Codes amp Data display for a carbureted engine RPM_ 1234 O2 mV __689 INTEGRATR_ 128 DIAGNOSTIC MODE DO NOT DRIVE NO CODES PRESENT O02 SENSOR B1 05 02 SENSOR B2 06 Figure 8 6 Sample GM Codes amp Data display for a fuel injected engine Data Lists
41. le speed output circuit 2000 All 4 8 5 3 6 0 ao induced chassis pitch circuit Table 8 2 Truck DTCs with multiple definitions sheet 2 of 2 DTCs with Multiple Definitions Trucks DTC YEAR 5th VIN ENGINE DEFINITION 1996 All 4 3 5 0 5 7 7 4 Oil level lamp fault P1653 1996 97 All 6 5 EGR vent solenoid circuit fault 1999 2000 All 6 5 7 4 EGR vent sol or EPR circuit P1654 1996 2001 All 6 5 7 4 Service throttle soon circuit Road Test C amp D Selecting ROAD TEST C amp D from the MAIN MENU GM ENGINE initiates what some service manuals may call the open or normal mode because the scan tool does not place a load across the ALDL connector as it does in the diagnostic mode Figure 8 8 RPM_ 1234 O2 mV __689 INTEGRATR_ 128 ROAD TEST MODE OK TO DRIVE NO CODES PRESENT O02 SENSOR B1 05 02 SENSOR B2 Figure 8 8 Sample Road Test C amp D mode screen Whether codes and data display in the Road Test mode depends on the PCM of the specific test vehicle If codes and data are available in Road Test mode the menu selection reads ROAD TEST C amp D If not the menu selection reads ROAD TEST NO C amp D Generally the same codes and data information displays in Road Test C amp D mode as those described for the Codes amp Data mode except for the following important differences e The scan tool does not place a resistive load on the ECM and the engine operates normally
42. lection displays DTCs that were detected when the last test was run Test Failed Since Code Cleared The TEST FAILED SINCE CODE CLEARED selection displays DTCs that set since the last time codes were cleared Failed This Ignition The FAILED THIS IGNITION selection displays DTCs that set during the current ignition cycle DTC Status The DTC STATUS selection offers a way to quickly check on the status of the OBD II tests associated with a particular DTC and verify related repairs P To check DTC status 1 Select DTC STATUS The display prompts you to enter the DTC Figure 8 18 DTC STATUS SCROLL IN DESIRED TROUBLE CODE TO TEST kk pQ000 Figure 8 18 Sample prompt to enter the DTC Select each correct number for the position indicated by the cursor Once all characters are selected the screen automatically updates to show the DTC status Figure 8 19 P0201 CYLINDER 1 INJECTOR CKT PROBLEM THIS IGNITION CYCLE RAN amp FAILED LAST TEST FAILED SINCE CLEAR__NOT RUN HISTORY YES MIL OR SVS REQ YES Figure 8 19 Sample DTC status display If a DTC supported by the vehicle is entered the first line of the display shows the DTC definition The next three lines include five information fields THIS IGNITION CYCLE indicates the OBD II test status related to the selected DTC There are four possible results RAN amp FAILED RAN amp PASSED NOT RUN and RAN amp INT RAN amp INT intermittent means t
43. les the solenoids on and off several times and after a few seconds the following screen displays Figure 8 74 SOLENOID BLEED PROCEDURE COMPLETE DURING NEXT PROCEDURE BRAKE PEDAL SHOULD BE FIRM amp NOT DROP EXCESSIVELY PRESS Y FOR SOLENOID CHECKOUT PROCEDURE Figure 8 74 Delco Moraine III solenoid bleed complete Continue applying pressure on the pedal and press Y The solenoid checkout screen displays Figure 8 75 SOLENOID CHECKOUT PROCEDURE NOW CYCLING EACH CHANNEL IF PEDAL DROP EXCESSIVE SUSPECT SOLENOID O RINGS IN PROGRESS Figure 8 75 Delco Moraine III solenoid checkout procedure If the brake pedal suddenly drops during this portion of the test suspect faulty solenoid O rings After a few seconds the following screen displays Figure 8 76 which indicates that the EBCM self test verified the integrity of the system and that it is now safe to bleed the Powermaster solenoids SOLENOID CHECKOUT PROCEDURE COMPLETE IF PEDAL DID NOT DROP EXCESSIVELY OK TO BLEED AIR FROM INBOARD SIDE BLEEDER SCREW ON POWERMASTER UNIT Figure 8 76 Delco Moraine III solenoid checkout procedure complete Bleed air from the inboard side bleeder screw Figure 8 77 Some units also have an outboard side bleeder screw If so bleed it too 177 Testing ABS Systems Figure 8 77 Powermaster III bleed screws A Inboard bleed screw B Outboard bleed screw Error Messages If the brake pedal is released a
44. list is fairly long so make sure to view the entire list A complete list is shown in Figure 8 60 167 168 Testing ABS Systems CODE HISTORY ABS BRAKING IS OFF OK TO DRIVE 11 ABS WARNING LAMP OPEN OR SHORT TO GND 28 EXCESSIVE RR WHEEL ACCELERATION LAST CODE SET 28 VEHICLE SPEED BRAKE SWITCH ON BRAKE LAMP 1ST CODE SET 11 NO OF TIMES NO OF IGN CYCLES SINCE LAST SET NO OF IGN CYCLES SINCE FIRST SET CODE SET 28 NO OF TIMES NO OF IGN CYCLES SINCE LAST SET NO OF IGN CYCLES SINCE FIRST SET 3RD CODE SET___ NONE NO OF TIMES NO OF IGN CYCLES SINCE LAST SET NO OF IGN CYCLES SINCE FIRST SET 4TH CODE SET__ NONE NO OF TIMES NO OF IGN CYCLES SINCE LAST SET NO OF IGN CYCLES SINCE FIRST SET 5TH CODE SET___ NONE NO OF TIMES SET_ NO OF IGN CYCLES SINCE LAST SET NO OF IGN CYCLES SINCE FIRST SET 5 7 5 0 0 0 0 0 0 0 0 0 Figure 8 60 Complete Delco Moraine code history In the sample list shown code 28 is the last code set and zero ignition cycles have occurred since it last set This means the code 28 is a currently present hard code Code 11 is shown as the first code set This code set twice 7 ignition cycles occurred since it last set and 15 ignition cycles occurred since it first set This means code 11 is an intermittent fault not currently present The second code code 28 set during five of the last five drive cycles and zero ignition cycles occurred since it last set This means code 28 is a
45. ltaneously switch from off to on when the Y button is pressed Be aware that the parameter on the screen is the PCM solenoid command The Y button grounds the solenoid independently of the PCM TPS Check and Adjustment Specifications The TPS CHECK AND ADJUSTMENT selection on the Functional Tests menu allows you to check and adjust the operation of the throttle position sensor The display varies for different vehicles but each gives the current TPS reading and the test or adjustment specification If engine speed is part of the adjustment specification alive RPM reading appears on the top line of the display If the TPS is not adjustable the voltage should be measured at curb idle or closed throttle and the scan tool displays allowable TPS voltage range IMPORTANT A To avoid incorrect TPS adjustment or component damage be sure to follow the on screen instructions Refer to a vehicle service manual for complete test or adjustment procedures P To perform a TPS check and adjustment 1 Select TPS CHECK AND ADJUSTMENT The first screen of a caution message displays Figure 8 29 151 152 Testing Control Systems Tests Except ABS CAUTION UNLESS NOTED OTHERWISE CHECK TPS WITH THROTTLE CLOSED KEY ON ENGINE WARM A C OFF NEVER ADJUST WITH ENGINE IDLING IN DIAGNOSTIC MODE PRESS Y Figure 8 29 First screen of the caution message 2 Press Y to continue with the message Figure 8 30 SOME TPS S ARE NOT ADJUSTABLE O
46. n both lamps light for about 2 seconds The antilock lamp goes out if no ABS faults are present If an ABS fault is present the antilock lamp stays lit or it lights as the ABS fault occurs The 4WAL EBCM recognizes both current hard and intermittent faults and stores soft codes in memory for intermittent problems The 4WAL EBCM transmits current codes and up to three history or soft codes in the Codes amp Data mode Data parameters for wheel speed sensors brake switches and other operating data are also provided The MULTI 1 universal adapter is required for testing the Kelsey Hayes 4WAL system with the 12 pin ALDL Connect the adapter as shown in Figure 8 63 A Figure 8 63 MULTI 1 adapter wire color codes for 4WAL testing A Green B Black For Kelsey Hayes 4WAL systems with the 16 pin DLC use the OBD II connector see Connecting to the Vehicle on page 132 Use the CLEAR ABS CODES selection on the Exit menu to erase codes from the 4WAL system 169 Testing ABS Systems 8 2 8 Rear Wheel Antilock RWAL Brakes Some 1993 95 trucks and vans transmit data over a serial data stream On these vehicles ABS CODES amp DATA is an available menu selection The Kelsey Hayes RWAL brake system used on 1988 and later trucks and vans has a red brake indicator lamp that acts as a warning lamp for both the basic brake system and the RWAL system The lamp lights for about 2 seconds when the ignition is turned on It the
47. n goes off unless the parking brake is applied The brake lamp remains on if the parking brake is applied or a if hydraulic brake problem exists The RWAL EBCM recognizes both current or hard and intermittent or soft faults and stores codes in memory for intermittent problems In normal operation the brake lamp is off if no faults are present If a RWAL problem exists the brake lamp stays on solidly or flashes a steady on off sequence with no apparent code pattern Selecting DISPLAY ABS CODES causes the brake lamp to begin flashing codes The codes are displayed on the lamp in a distinct pattern of long and short flashes P To read codes e Select DISPLAY ABS CODES mode and count the first long flash and all short flashes For example one long flash followed by five short flashes is code 6 The long flash indicates that a code number is starting or repeating The RWAL system flashes only one code at a time in the display ABS codes mode but repeats that one code as long as the scan tool remains in this test mode If multiple codes are present the first code must be repaired before any other codes display NOTE If no codes are present and the brake lamp is not lit reading codes in the Display ABS Codes mode sets a false code 9 vehicle speed signal RWAL systems do not display a system pass code A code 9 is set if there are no other codes present in the system This happens because the speed sensor circuit is the diagnostic circu
48. ngine lamp stops flashing code 12 and new trouble codes cannot set The PCM also sets timing to a fixed degree of advance which allows for checking and adjusting ignition timing for some engines Field Service mode may also be used to conduct a system performance check on carbureted engines See the vehicle service manual for details e Ona fuel injected engine running in the Field Service mode the check engine lamp flashes rapidly when the engine is running in open loop and slowly when in closed loop The length of the check engine lamp flash indicates whether the exhaust is rich or lean in closed loop The flash is longer if rich Access On board Diagnostics The ACCESS ON BOARD DIAGNOSTICS selection creates an open circuit between the ALDL diagnostic and ground pins or pins A and B Figure 8 26 This selection is available on the following systems e 1981 and later Cadillac e 1986 and later Buick Riviera Buick Riatta Oldsmobile Toronado and Oldsmobile Trofeo ECM IS REMOVED FROM DIAGNOSTIC MODE TO ALLOW ACCESS TO ON BOARD DIAGNOSTICS REFER TO VEHICLE SERVICE MANUAL FOR PROPER PROCEDURES PRESS N TO EXIT Figure 8 26 Sample access onboard diagnostics screen This allows access to the onboard diagnostics without disconnecting the scan tool Refer to GM service procedures to enter and use the onboard diagnostic program Air Solenoid The AIR SOLENOID selection energizes the air switching solenoid to direct air into the exhau
49. on and allow the pump to establish system pressure Note whether the antilock lamp turns off in 30 seconds or less 2 With the scan tool connected switch the ignition off Select DISPLAY ABS CODES Switch the ignition on and watch the antilock lamp Ifthe lamp turns on and then off in about 4 seconds no codes are present The system does not have a system pass code Ifthe lamp turns on for 4 seconds and then starts flashing codes are present 5 Ifthe lamp flashes count the flashes until there is a 3 second pause This is the first digit of the code Count flashes after the 3 second pause this is the second digit Count only the number of times the lamp turns on and off for the second digit After the second digit the lamp lights constantly Do not count this as a code digit 6 After the antilock lamp stops flashing the code and stays on press N to exit from display ABS codes Without switching the ignition off press Y to reenter and read any additional codes 7 Enter codes flashed by the antilock lamp into the scan tool as previously explained in the How To Enter Codes section The antilock lamp remains on continuously in display ABS codes mode once all codes have been displayed Ro Clearing Teves Il Codes The Teves II EBCM EBTCM does not allow codes to be cleared until repairs have been made Therefore do not attempt to clear codes until repairs are complete Disconnecting the battery or the EBCM EBTCM
50. one of three ways depending upon the vehicle The main menu selections are e Codes amp Data e Codes e Code History If the test vehicle has a CODES ONLY selection on the MAIN MENU GM ABS the display appears similar to Figure 8 57 CODE LIST CODES ONLY OK TO DRIVE C0221 RF WHEEL SPEED SENSOR CKT OPEN END OF LIST Figure 8 57 Sample Bosch or Delco Bosch 5 0 or 5 3 code display If the CODE HISTORY selection is available the DTC displays along with certain data parameters that reflect conditions present at the time the code set Selecting CODE HISTORY places the EBCM in diagnostic mode and new codes cannot be set 165 166 Testing ABS Systems The CODE HISTORY selection works the same for Bosch 5 and Delco Bosch 5 as it does for Bosch 2 described on Bosch 2 Trouble Codes on page 164 8 2 4 Delco Moraine III Codes amp Data 1988 91 The Delco Moraine III system is fully functional in the Codes amp Data mode If faults are present the EBCM may disable either just front ABS operation or the entire system Because problems may be present at the time of testing the second line of the display advises ABS braking is off However the service brakes operate normally and the vehicle may be driven The system does set new codes in this mode Full ABS braking is available if no problems have disabled the system On a Delco Moraine III system the top line of the displays the current position of the
51. onic hydraulic control unit EHCU solenoids on Delco Moraine III ABS Figure 8 70 GM manuals refer to this as ABS solenoid bleed and checkout test MAIN MENU GM ABS READ THIS FIRST gt ABS CODES amp DATA FUNCTIONAL TESTS EXIT amp RE ID CUSTOM SETUP Figure 8 70 MAIN MENU GM ABS for Delco Moraine III CAUTION Failure to follow proper brake bleeding procedures may result in improper brake system operation or brake system failure NOTE i This procedure bleeds only the Powermaster III solenoids not the base brake system or lines Refer to GM service manuals for additional information P To bleed Powermaster Ill solenoids 1 Open the Delco Moraine III Functional Tests menu Figure 8 71 SELECT TEST MODE PRESS Y TO CONTINUE gt BLEED POWERMASTER SOLENOIDS Figure 8 71 Delco Moraine III Functional Tests menu 2 Switch the key on with the engine off 3 Select BLEED POWERMASTER SOLENOIDS The first instructional screen displays Figure 8 72 DEPRESS BRAKE PEDAL HALF WAY DURING ENTIRE PROCEDURE WARNING WHEELS MUST NOT ROTATE PRESS Y TO CONTINUE Figure 8 72 First Delco Moraine III brake bleeding instruction 4 Apply medium pressure to the pedal and press Y The next bleeding instruction displays Figure 8 73 176 SOLENOID BLEED PROCEDURE NOW CYCLING SOLENOIDS TO RELEASE TRAPPED AIR IN PROGRESS Figure 8 73 Second Delco Moraine III brake bleeding instruction The scan tool cyc
52. or Kelsey Hayes RWAL 8 2 10 Teves Il ABS Codes amp Data 1986 91 The Teves II ABS displays codes by flashing the amber antilock indicator lamp on the instrument panel These vehicles have both a red brake indicator lamp and an amber antilock indicator lamp on the instrument panel The lamps light in various combinations to indicate normal and abnormal brake system conditions Additionally models with driver information center panels display warning messages as described in the following paragraphs Normal Startup Messages and Lamp Operation On models without a driver information center the brake and antilock lamps both light for 4 to 5 seconds when the ignition is first turned on Both lamps go out while the engine is cranking As the engine starts and the key returns to the run position the antilock lamp may stay on for 3 or 4 seconds If the vehicle was parked for a long period such as overnight both the brake and antilock lamps may stay lit for up to 30 seconds while the ABS pump recharges the system to normal pressure When a model with a driver information center is started the brake and antilock lamps both light as well plus antilock disabled and traction disabled messages appear for a few seconds The lamps turn off and the messages change to antilock OK and traction OK once the ABS pump recharges the system to normal pressure Again if the vehicle was parked for a long time such as overnight
53. st manifold Use this test to check the operation of the O2S and the response of the MC solenoid or the fuel integrator block learn and injector pulse width NOTE The engine must be warmed up and operating in closed loop for this test to be valid The PCM must be directing air downstream to the catalytic converter This test cannot be performed reliably when the PCM is directing the air divert solenoid to route air to the atmosphere To perform an air solenoid test 1 Select AIR SOLENOID A caution message now displays Figure 8 27 CAUTION THIS TEST DIVERTS AIR TO EXHAUST MANIFOLD WHILE Y IS PRESSED MAX TIME 20 SECONDS PRESS Y TO ENTER TEST THEN PRESS Y FOR AIR INJECTION Figure 8 27 Sample air solenoid test caution 2 Press Y to continue The air solenoid test screen displays which is the standard Codes amp Data display 3 Press and hold Y to activate the test and the air switching solenoid directs air to the exhaust manifold With Y held AIR appears on the left side of the top line Figure 8 28 AIR RPM_1234 0O2 mV __689 MC DWL _ 38 AIR TEST DO NOT DRIVE NO CODES PRESENT O2 CROSSCOUNTS 08 OPEN CLSD LOOP__OPEN Figure 8 28 Sample active AIR solenoid test screen While the test is active a timer counts how long the Y button is held The scan tool automatically turns off air switching after 20 seconds of continuous operation The AIR switch solenoid parameter value on the screen does not simu
54. state only once for each ignition cycle During ABS testing in Codes amp Data mode other vehicle components may seem to operate abnormally i e the instrument panel may appear to stop working or the gauge readings may change randomly This is normal and stops when the EBCM is taken out of the diagnostic state NOTE ABS testing may cause false DTCs to appear on the engine code list After ABS testing reenter vehicle ID for engine testing and check the engine code list Clear any codes that may be present and recheck to be sure they were false Bosch 2 Trouble Codes The 1992 94 Corvette uses a Bosch 2 ABS that provides code history information separately from the ABS data For these vehicles CODE HISTORY is a MAIN MENU GM ABS selection New codes cannot be set while the system is in diagnostic mode If codes are present the third line changes to read scroll down for ABS codes Scrolling reveals a code number and description along with certain conditions that relate to the code Figure 8 55 35 LEFT REAR WHEEL SPEED SENSOR CONDITIONS AT TIME OF ABOVE FAULT CODE BRAKE SW OPEN STARTS SINCE CODE_16 ABS STATE OFF VEH SPEED MPH 47 Figure 8 55 Sample Bosch 2 display with codes When a code sets the EBCM records three operating conditions e Brake switch state to indicate if the brakes were applied e ABS state to indicate if ABS was operational e Vehicle speed Additionally the EBCM records the number of times the ve
55. sting of functional tests for 1995 and earlier models e Field Service Mode e Access Onboard Diagnostics e AIR Solenoid Force AIR to Exhaust e TPS Check and Adjustment Specifications e Backup Fuel e Full Lean FL Mixture e Full Rich FR Mixture e Backup Spark and Fuel e Fixed 10 Spark WARNING Do not enter any functional test while driving on a road test During some functional tests the PCM makes changes to ignition timing fuel delivery and other engine functions which may affect engine operation and vehicle control Field Service Selecting FIELD SERVICE on 1993 and earlier models grounds Pin B of the ALDL connector to enter Field Service mode The PCM does not transmit data and the vehicle does not set new codes in Field Service mode Figure 8 25 On some vehicles field service is used to check or adjust ignition timing and the idle minimum air rate FIELD SERVICE MODE WITH KEY ON ENGINE OFF CE LAMP FLASHES TROUBLE CODES AND SOME ECM OUTPUTS ARE EXERCISED PRESS N TO EXIT Figure 8 25 Sample field service screen With the key on and the engine off the check engine lamp flashes DTCs if any are present or code 12 if there are no codes The PCM also energizes all solenoids with the key on and the engine off so Field Service mode may be used to test solenoid operation 149 150 gt Testing Control Systems Tests Except ABS e On acarbureted engine running in the Field Service mode the check e
56. t any time during the bleed sequence the functional test procedure aborts and a warning displays Figure 8 78 WARNING BRAKE PEDAL MUST BE DEPRESSED HALF WAY DURING ENTIRE PROCEDURE PRESS N FOR FUNCTIONAL TESTS MENU Figure 8 78 Test aborted due to brake pedal release message Attempt to drive the vehicle at any time during the bleeding procedure and test procedure aborts and a warning displays Figure 8 79 WARNING PROCEDURE CANNOT BE RUN WHILE WHEELS ARE MOVING PRESS N FOR FUNCTIONAL TESTS MENU Figure 8 79 Test aborted due to vehicle movement message In addition pressing the N button at any time during the procedure aborts the functional test and the scan tool displays a warning Figure 8 80 USER ABORTED PROCEDURE PRESS N FOR FUNCTIONAL TESTS MENU Figure 8 80 Test aborted by operator message 178 8 2 15 Read This First Instructions NOTE This selection should always be opened and read before working with any GM antilock brake system for the first time This selection contains specific information about ABS identification control module communication and reading and clearing codes These instructions provide a reference for testing a new system or for reviewing facts for a system you work on infrequently 179 Chapter 8 GM Testing ABS Systems 180
57. t occurred during the current ignition cycle If the ignition is turned off codes for recent intermittent faults are lost and not displayed Follow the procedure below for a vehicle with a Delco Moraine III system with the amber antilock warning lamp on P To view intermittent faults 1 Do not turn the ignition off 2 Connect the scan tool to the vehicle with the engine running 3 Enter the vehicle ID 4 Select ABS CODES amp DATA from the MAIN MENU GM ABS 8 2 5 Delco Moraine VI Codes amp Data 1991 2001 The ABS Codes amp Data display for Delco Moraine VI functions similarly to Delco Moraine III systems however some of the displayed parameters differ This system also provides code history data or soft codes in addition to the current code or hard code data The Delco Moraine VI system data display includes The last or most recent code that set The number of ignition cycles since the last code set The sensed vehicle speed at the time the last code set The first five codes set display from oldest to newest The number of times each code set The number of ignition cycles since each code last set The number of ignition cycles since each code first set In addition brake switch and the ABS stop data parameters also display The last code set data is not updated by the ABS system unless vehicle soeed exceeds 10 MPH 16 KPH Selecting CODE HISTORY from the MAIN MENU GM ABS displays a data list This
58. under ECM control it is safe to drive the vehicle for troubleshooting intermittent problems e Some vehicles do not display codes in the Road Test mode e The data list may differ from that of the list in Diagnostic mode For example some fuel injected engines display a slightly shorter data list in Road Test mode Limited Data in Road Test Some GM vehicles do not provide DTCs in Road Test mode as indicated by a no codes available in this mode message Most vehicles that do provide DTCs display a shorter list in Road Test mode You will need to select CODES amp DATA from the MAIN MENU GM ENGINE to view all DTCs available for these vehicles Road Test No C amp D Several GM engine ECMs particularly on vehicles with carbureted engines provide a Road Test mode but do not transmit data For these vehicles CODES amp DATA and ROAD TEST are separate selections on the MAIN MENU GM ENGINE Figure 8 9 143 Testing Control Systems Tests Except ABS MAIN MENU GM ENGINE PRESS N FOR HELP gt CODES amp DATA ROAD TEST NO C amp D FUNCTIONAL TESTS REVIEW MOVIE CUSTOM SETUP Figure 8 9 Sample main menu when data does not transmit during a Road Test The ROAD TEST NO C amp D selection removes the resistive load the scan tool applies in Codes amp Data mode and allows the vehicle to be safely driven with the scan tool connected After selecting ROAD TEST NO C amp D the following screen displays Figure 8 10 ROAD TE

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