Article No. 01-9-7 Emissions/Engine Controls
Contents
1. Leaking contaminated fuel injectors or fuel pressure regulator Low fuel pressure or running out of fuel fuel pump concem fuel supply ne restrictions low fuel level etc Vapor recovery system stuck VMV etc Induction System MAF contamination Alr leaks between MAF and throttle plate PCV system Other vacuum leaks elmproperly seated engine oil dipstick EGR System eLeaking gasket Stuck EGR valve Leaking diaphragm or elncorract cylinder compression Exhaust leaks before or near the HO2S eSecondary alr stuck on HEATED OXYGEN SENSOR HO2S MONITOR HO2S LACK OF SWITCHING P1131 Lack of HO2S 11 Switch When an HO2S sensor indicates See Possible Causes for DTC P1130 Indicates Lean lean at the end of a test the system is trying to correct for an over lean condition The code is set when the fuel control system no longer detects switching for a calibrated amount of time P1132 Lack of HO2S 11 Switch When an HO2S sensor indicates See Possible Causes for DTC P1130 Indicates Rich rich at the end of a test the system is trying to correct for an over rich condition The code is set when the fuel control system no longer P1137 Lack of HO2S 12 Switch The downstream HO2S sensors are ePinched shorted or corroded wiring and Sensor Indicates Lean forced rich and lean and monitored pins by the PCM The code is set if the PCM does not detect the output of Crossed sensor wires bia HO22. The H025 detects the presence of oxygen in the exhaust and provides the PCM with feedback indicating a rich or lean condition A correction factor is added to the fuel injector pulsewidth calculation according to the Long and Short Term Fuel Trims as needed to compensate for variations in the fuel system When deviation in the parameter LAMBSE increases air fuel control suffers and emissions increase When LAMBSE exceeds a calibrated limit and the fuel trim table has clipped reached adaptive limit the Fuel System Monitor sets a DTC The MIL is activated after a fault is detected on two consecutive OBD II drive cycles The Fuel System Monitor DTCs can be categorized as follows Fuel Delivery Error P0148 Lean shift in fuel system operation P0171 Bank 1 and P0174 Bank 2 Rich shift in fuel system operation P0172 Bank 1 and P0175 Bank 2 FUEL SYSTEM MONITOR Diagnosi Trouble Code P0148 Fuel Delivery Error At least one bank lean at wide open throttle P0171 System Too Lean Bank 1 The Adaptive Fuel Strategy continuously monitors fuel delivery hardware The code is set when the adaptive fuel tables reach a rich calibrated limit P0174 System Too Lean Bank 2 Same as DTC P0171 but Bank 2 Fuel System Severely restricted fuel fitter Severely restricted fuel supply line Fuel System Contaminated fuel injectors eLow fuel pressure or running out of fuel fuel pump filter fue supply line
3. oignon Trte code Devcon Posse cusses P0131 HO2S Sensor Circuit Out of Range Low Voltage HO2S 11 6 i GaS angor or oa coolant water silicone fuel oil etc Chafed damaged wiri testing and DTC P0131 is present 9 the PCM will be in FMEM Crossed HO2S signal signal retum wiring PCM P0136 HO2S Sensor Circuit The downstream HO2S sensor s Disconnected sensor Malfunction HO2S 12 are continuously checked for maximum and minimum voltages Pinched shorted corroded wiring or pins The code will set when the voltages orocced sensor wires fail to meet the calibrated limits Exhaust leaks Contaminated or damaged sensor eChafed damaged wiring P0151 HO2S Sensor Circuit Out Same as DTC P0131 but Bank 2 See Possible Causes for DTC P0131 of Range Low Voltage HO2S 21 P0156 HO2S Sensor Circuit Same as DTC P0136 but Bank 2 See Possible Causes for DTC P0136 Malfunction HO2S 22 HEATED OXYGEN SENSOR HO2S MONITOR HO2S SIGNAL CIRCUIT MALFUNCTION P0135 HO2S Sensor Heater During testing the HO2S heaters Blown fuse Circuit Malfunction HO2S 11 are checked for opens shorts and excessive current draw The code Short to VPWR in hamess or HO2S will set when current draw exceeds swater in harness connector a maximum Calibrated limit or falls below a minimum calibrated limit Open VPWR or GND circuit and or an open or short is detected eLow battery voltage Poor electrical
4. restrictions Vapor recovery system VMV Induction System MAF contamination eAir leaks between the MAF and throttle body Vacuum leaks PCV system concem elmproperly seated engine oil dipstick EGR System eLeaking gasket Stuck EGR valve eLeaking diaphragm or EVA Base Engine Exhaust leaks before or near the HO2S Secondary air concen Powertrain Control System PCM concern See Possible Causes for DTC P0171 FUEL SYSTEM MONITOR Digronic Trouble Code omenpien posebe Cases P0172 System Too Rich Bank 1 The Adaptive Fuel Strategy continuously monitors fuel delivery hardware The code sets when the adaptive fuel tables reach a lean calibrated limit P0175 System Too Rich Bank 2 Same as DTC P0172 but Bank 2 Fuel System eExcessive fuel pressure eLeaking contaminated fuel injectors Vapor recovery system concern Base Engine Oil overfill Cam timing concern sLow cylinder compression Excessive engine wear See Possible Causes for DTC P0172 E2 Fuel System Monitor Diagnostic Trouble Codes Article No 01 9 7 Emissions Engine Controls Driveability Diagnosis F DIAGNOSTIC SERVICE TIPS 1 Always reset KAM after performing a repair After performing a repair on a vehicle with the MIL on and or DTCs present always clear KAM When a malfunction is present the PCM adapts attempts to correct for this condition Once the vehicle has been repaired if the KAM is not rese
5. the engine may not be Examples Exhaust system leaks upstream or near HO2S malfunctioning Secondary Air Injection system d MAF concerns If a MAF concern is suspected see TSB 98 23 10 4 Checking fuel pressure Check fuel pressure with engine under a load when diagnosing a lean concern A partially plugged fuel filter can be difficult to detect and can be easily overlooked if fuel pressure is only checked at idle The same is true for other types of fuel supply concerns e g bent or kinked lines degraded fuel pump At idle an engine requires only a small volume of fuel Due to the fact that there is a small volume of fuel needed at idle a restriction in the fuel supply line in many cases will not cause the fuel pressure to be low When the vehicle is under a load the engine requires much more fuel than at idle Under a load a restriction in the fuel supply line will prevent the high rate of fuel flow that is needed to maintain the correct fuel pressure
6. air when the engine is cold might be the best starting point Examples Loose leaking or disconnected vacuum lines intake manifold gaskets or O rings throttle body gaskets brake booster air inlet tube stuck frozen aftermarket PCV valve unseated engine oil dipstick MAF reading lower than normal etc b Insufficient fueling In this type of condition the engine may actually run lean of stoichiometry 14 7 1 air fuel ratio if the PCM is not able to compensate enough to correct for the condition This condition is typically caused by a fuel delivery system concern that restricts or limits the amount of fuel being delivered to the engine This condition will normally be most apparent when the engine is under a heavy load when a higher volume of fuel is required If Freeze Frame Data indicates that the fault occurred under a heavy load a check of the fuel delivery system checking fuel pressure with engine under a load might be the best starting point Examples Low fuel pressure fuel pump fuel filter fuel leaks restricted fuel supply lines fuel injector concerns etc c Exhaust system leaks In this type of condition the engine may actually be running near stoichiometry 14 7 1 air fuel ratio but the exhaust gas mixture will be lean This condition is caused by oxygen rich air entering the exhaust system through an external source This condition will cause the exhaust gas mixture to be lean even though the actual combustion in
7. damage or contamination Do not use power tools in the removal or installation of sensors Use a 22mm wrench or crow foot to remove and install H025 sensors do not use slotted sockets as these sockets may damage wires H025 sensors should be torqued to 41 5 N m 30 4 lb ft 3 Do not replace downstream HO2S sensors H02S12 H02S22 for DTCs P0420 and or P0430 When diagnosing a vehicle with a customer concern of MIL On and DTCs P0420 P0430 in continuous memory do not replace the downstream HO2S sensors H02S12 H02S22 Damaged or malfunctioning downstream HO2S sensors will not cause these DTCs to be set Always verify the vehicle concern then perform the pinpoint diagnostics in the appropriate PC ED Service Manual F4 Tips Related to the Fuel System Monitor 1 HO2S sensors are not likely to be the cause of adaptive DTCs P0171 P0172 P0174 P0175 Most warranty returned HO2S sensors replaced for these DTCs are found to function normally Additional related DTCs will normally be present if there is a concern with the HO2S sensors Do not replace an HO2S sensor unless verified through pinpoint diagnostic tests found in the PC ED Service Manual 2 DTCs P0171 P0172 P0174 and P0175 are not related to downstream H028 sensors When diagnosing a vehicle with a MIL On and DTC s P0171 P0172 P0174 and or P0175 in continuous memory do not replace the downstream HO2S sensors These DTCs have no connection to the downstream HO2S sensor fu
8. 12 to Bank 2 HO2S 22 Same as DTC P1128 but downstream Crossed HO2S harness connectors Bank to Bank upstream Crossed HO2S wiring at 104 pin PCM connector or at the HO2S connectors See Possible Causes for DTC P1128 C2 Heated Oxygen Sensor HO2S Monitor Diagnostic Trouble Codes Article No 01 9 7 Emissions Engine Controls Driveability Diagnosis D CATALYST EFFICIENCY MONITOR D1 Catalyst Efficiency Monitor Information The Federal Test Procedure Catalyst Monitor monitors for deterioration in the catalyst system and illuminates the MIL when tailpipe emissions exceed the appropriate HC emission thresholds The Catalyst Monitor is enabled after the upstream and downstream HO2S sensors have been tested and verified to be functional This monitor relies on the front and rear heated oxygen sensors HO2S to infer catalyst efficiency based upon oxygen storage capacity Under normal closed loop fuel conditions high efficiency catalysts have oxygen storage which makes the switching frequency of the rear HO2S quite slow compared with the frequency of the front HO2S As catalyst efficiency deteriorates its ability to store oxygen declines and the rear HO2S begins to switch more rapidly approaching the frequency of the front sensor In general as catalyst efficiency decreases the switch ratio increases from a switch ratio of 0 for a low mileage catalyst to a switch ratio of 0 8 or 0 9 for a low efficiency catalyst Some v
9. 2S voltage amplitude and output response frequency are observed A sample of the upstream HO2S signal is evaluated to determine if the sensor is capable of switching or has a slow response rate An HO2S heater circuit fault is determined by turning the heater on and off and looking for a corresponding change in the OSM and by measuring the current going through the heater circuit The MIL is activated after a fault is detected on two consecutive OBD II drive cycles The HO2S Monitor DTCs can be categorized as follows HO2S signal circuit malfunction P0131 P0136 P0151 P0156 HO2S slow response rate P0133 P0153 HO2S heater circuit malfunction P0135 P0141 P0155 P0161 Downstream HO2S not running in on demand self test P1127 Swapped H025 connectors P1128 and P1129 H025 lack of switching P1130 P1131 P1132 P1150 P1151 P1152 HO2S lack of switching sensor indicates lean P1137 H025 lack of switching sensor indicates rich P1138 HEATED OXYGEN SENSOR HO2S MONITOR HO2S LACK OF SWITCHING P1130 Lack of HO2S 11 Switch Fuel Trim at Limit switching The code will set when i the HO2S fails to switch due to Short to VPWR or VREF in harness or HO2S HO2S circuit shorted to Ground Corrosion or poor mating terminals and wiring Damaged HO2S Damaged PCM other DTCs should be present Fuet System Excessive fuel pressure stuck fuel pressure regulator restricted fuel return lines etc
10. Article No 01 9 7 Emissions Engine Controls Driveability Diagnosis 05 14 01 14 mai 2001 Emissions Engine Controls Driveability Diagnosis Index Information A Description of Terms and Acronyms B HO2S Location Diagrams C Heated Oxygen Sensor HO2S Monitor D Catalyst Efficiency Monitor E Fuel System Monitor F Diagnostic Service Tips DRIVEABILITY H025 HEATED OXYGEN SENSOR CATALYST AND FUEL SYSTEM MONITORS SERVICE TIPS OBD II VEHICLES ONLY FORD 1994 1997 THUNDERBIRD 1994 2001 MUSTANG 1995 2001 CROWN VICTORIA 1996 1997 PROBE 1996 2000 CONTOUR 1996 2001 ESCORT TAURUS 2000 2001 FOCUS 1994 1997 F SUPER DUTY F 250 HD F 350 1995 2001 ECONOLINE RANGER WINDSTAR 1996 BRONCO 1996 1997 AEROSTAR 1996 2001 EXPLORER 1997 2001 EXPEDITION F 150 F 250 LD 1999 2001 SUPER DUTY F SERIES 2000 2001 EXCURSION 2001 ESCAPE LINCOLN 1995 2001 CONTINENTAL TOWN CAR 1996 1998 MARK VIII 2000 2001 LS 1998 2001 NAVIGATOR MERCURY 1994 1997 COUGAR 1995 2001 GRAND MARQUIS 1996 1999 TRACER 1996 2000 MYSTIQUE 1996 2001 SABLE 1999 2001 COUGAR 1997 2001 MOUNTAINEER ISSUE This article is intended to be an aide in diagnosing conditions related to Heated Oxygen Sensor HO2S Catalyst and Fuel System Monitor related Diagnostic Trouble Codes DTCs Additional information is included to assist in diagnosing certain vehicle symptoms This article is NOT intended to be a shortcut to the Po
11. Engine Coolant Temperature Sensor or PID EGR Exhaust Gas Recirculation EEC Electronic Engine Control EVR EGR Vacuum Regulator FMEM Failure Mode Effects Management GND Ground HC Hydrocarbons HO2S Heated Oxygen Sensor or PID IAT Inlet Air Temperature Sensor or PID KAM Keep Alive Memory KOEO Key On Engine Off KOER Key On Engine Running LONGFT Long Term Fuel Trim MAF Mass Air Flow Sensor or PID MIL Malfunction Indicator Lamp Check Engine NGS New Generation Star Tester Scan Tool OBD II On Board Diagnostics II OSM Output State Monitor PC ED Powertrain Control Emissions Diagnosis PCM Powertrain Control Module PCV Positive Crankcase Ventilation PID Parameter Identification Display RAM Random Access Memory RPM Revolutions Per Minute SHRTFT Short Term Fuel Trim Stoichiometric 14 7 1 Air Fuel Ratio Gasoline Engines TP Throttle Position Sensor or PID VMV Vapor Management Valve VPWR Vehicle Power Battery Voltage VREF Vehicle Reference Voltage 5 volts Article No 01 9 7 Emissions Engine Controls Driveability Diagnosis B HO2S LOCATION DIAGRAMS HO25 21 UPSTREAM Figure 1 Article No 01 9 7 Emissions Engine Controls Driveability Diagnosis C HEATED OXYGEN SENSOR HO2S MONITOR C1 Heated Oxygen Sensor HO2S Monitor Information X UPSTREAM DOWNSTREAM pr SS a o RA Fi
12. S in a calibrated amount of c baust leaks Contaminated or damaged sensor P1138 Lack of HO2S 12 Switch Same as DTC P1137 but indicating See Possible Causes for DTC P1137 Sensor Indicates Rich rich P1150 Lack of HO2S 21 Switch Same as DTC P1130 but opposite See Possible Causes for DTC P1130 Fuel Trim at Limit bank P1151 Lack of HO2S 21 Switch Same as OTC P1131 but opposite See Possible Causes for DTC P1130 indicates Lean bank P1152 Lack of HO2S 21 Switch Same as DTC P1132 but opposite See Possible Causes for DTC P1130 Indicates Rich bank HEATED OXYGEN SENSOR HO2S MONITOR HO2S SLOW ee RATE Diagnostic Tovble Code P0133 HO2S Sensor Circuit Slow The HO2S monitor checks the Response HO2S 11 HO2S sensor frequency and amplitude If during testing the MAF sensor On 4 cylinder engines if P0133 is present this could be caused by a MAF issue on 6 and 8 cylinder engines this could only be a MAF issue if P0133 and P0153 are both present Exhaust leaks upstream or near HO2S HO2S Concerns Contaminated HO2S sensor contamination from the use of silicone based cleaners and sealants leaded fuel excessive oil consumption etc Deteriorating MO2S sensor P0153 HO2S Sensor Circuit Slow Same as DTC P0133 but Bank 2 Response HO2S 21 See Possible Causes for OTC P0133 HEATED OXYGEN SENSOR HO2S MONITOR HO2S SIGNAL CIRCUIT MALFUNCTION
13. component wear etc F3 Tips Related to Catalyst Efficiency Monitor 1 Determining catalyst efficiency switch ratio EXAMPLE OF AN EFFICIENT CATALYST UPSTREAM HO2S DOWNSTREAM HO2S NAN U U THREE WAY CATALYST am 125 7 NUMBER OF NUMBER OF SWITCHES SWITCHES DOWNSTREAM HO2S UPSTREAM HO2S CATALYST EFFICIENCY Figure 5 EXAMPLE OF AN INEFFICIENT CATALYST UPSTREAM HO2S DOWNSTREAM HO2S NAN THREE WAY CATALYST N VU 125 115 NUMBER OF NUMBER OF SWITCHES SWITCHES DOWNSTREAM HO2S UPSTREAM HO2S SWITCH RATIO TB 6247 A Figure 6 The upstream H025 sensors will have a high switch frequency due to normal closed loop fuel control With an efficient catalyst the downstream H025 will have a low switch frequency The switch ratio is determined by dividing the number of downstream switches by the number of upstream switches over a given period of time As the catalyst ages or if the catalyst is damaged or contaminated the downstream switches will increase When the downstream switch rate crosses a threshold value approximately 0 75 switch ratio a code is stored P0420 and or P0430 and the MIL illuminates refer to Figures 5 and 6 NOTE IF A CATALYST IS DETERMINED TO HAVE LOW EFFICIENCY AND REQUIRES REPLACEMENT REPLACEMENT OF THE DOWNSTREAM H025 SENSORS WILL NOT BE NECESSARY 2 Use care in handling H025 sensors In the event of catalyst replacement use care in the handling of H025 sensors to prevent
14. connections from PCM to HO2S sensor HO2S heater PCOM P0141 HO2S Sensor Heater Same as DTC P0135 but See Possible Causes for DTC P0135 Circult Malfunction HO2S 12 downstream Bank 1 P0155 HO2S Sensor Heater Same as DTC P0135 but Bank 2 See Possible Causes for DTC P0135 Circuit MaMunction HO2S 21 P0161 HO2S Sensor Heater Same as DTC P0141 but See Possible Causes for DTC P0135 Circuit Malfunction HO2S 22 downstream Bank 2 HEATED OXYGEN SENSOR HO2S MONITOR EXHAUST TEMPERATURE OUT OF RANGE 02 SENSOR TEST NOT COMPLETED Diagnose Trouba Ga P1127 Exhaust Not Warm Enough Downstream Sensor Not Tested The HEGO monitor uses an exhaust temperature model to is set when the inferred exhaust temperature is below a minimum calibrated value determine when the HO2S heaters can safely be turned on The code Engine not operating long enough prior to performing KOER self test Exhaust temperature not warm enough Pre existing P0135 P0141 P0155 PO161 HEATED OXYGEN SENSOR H025 MONITOR SWAPPED HO2S CONNECTOR Diagnostic Trouble Code Description P1128 Upstream Oxygen Sensors The HEGO monitor checks and Swapped from Bank 1 HO2S 11 to determines if the HO2S signal Bank 2 HO2S 21 response for a KOER fuel shift corresponds to the correct engine bank The code is set when the expected HOZS response is seen on the opposite bank P1129 Downstream Oxygen Sensors Swapped from Bank 1 HO2S
15. cuit wiring or splice It is highly unlikely that multiple sensors would fail at the same time When multiple DTCs of this nature are encountered reviewing the appropriate wiring diagram s can help to isolate possible areas of concern When reviewing the wiring diagram look for things that the affected sensors have in common IGNITION SWITCH T DOWNSTREAM p no2s HEATERS HEATERS POWERTRAIN L Figure 2 In this example the most likely cause of DTCs P0135 and P0155 with no other DTCs present would be a concern with Splice B refer to Figure 2 NOTE THIS ILLUSTRATION IS ONLY AN EXAMPLE SPLICE NAMES A B AND C ARE USED IN THIS EXAMPLE FOR CONVENIENCE ONLY ON AN ACTUAL VEHICLE SPLICE NAMES WILL DEPEND ON THE CIRCUIT NUMBER FOR THE VEHICLE UNDER REPAIR NOTE ALSO THAT THIS FIGURE IS NOT INTENDED TO SHOW ALL SPLICES CONNECTIONS ON ALL VEHICLES OTHER EEC CIRCUITS NOT SHOWN MAY ALSO BE SPLICED IN WITH THE CIRCUITS SHOWN X UPSTREAM DOWNSTREAM i Figure 3 TB 6245 A Figure 4 4 View H025 PID data carefully NGS PIDs for HO2S sensors that do not exist with certain exhaust configurations will show a value of 0 volts refer to Figures 3 and 4 In this example the vehicle equipped with a 4 cylinder engine has one upstream and one downstream HO2S Notice that the NGS scan tool display shows two upstream and two downstream HO2S PIDs and
16. ehicles will monitor substantially less than the entire catalyst volume in order to meet the stringent catalyst monitoring malfunction thresholds In many cases only the front light off catalyst is monitored Front and rear HO2S switches are counted under specified closed loop fuel conditions After the required number of front switches are obtained a rear to front HO2S switch ratio is calculated The switch ratio is compared against a threshold value If the switch ratio is greater than the calibrated maximum limit the catalyst has failed The test entry conditions for the Catalyst Efficiency Monitor are as follows ECT or CHT warmed engine IAT not at extreme ambient temperatures MAF greater than minimum engine load VSS within vehicle speed window and TP at part throttle are required Because an exponentially weighted moving average is used for malfunction determination up to six OBD II drive cycles may be required to illuminate the MIL NOTE THE CATALYST MONITOR ON SOME EARLY OBD II VEHICLES SOME 1994 1996 VEHICLES WAS REFERRED TO AS THE STEADY STATE CATALYST MONITOR AS OPPOSED TO THE FTP CATALYST MONITOR DESCRIBED ABOVE THAT IS MOST COMMON FOR VEHICLES BUILT AFTER 1996 BELOW IS A BRIEF DESCRIPTION OF THE STEADY STATE CATALYST MONITOR The Steady State Catalyst Monitor performs a 20 second test during steady state rpm and load conditions The Monitor transfers closed loop fuel control from the front to the rear 02 senso
17. gure 3 The H025 Monitor is an on board strategy designed to monitor the HO2S sensors for a malfunction or deterioration that can affect emissions Under specific conditions the fuel control or upstream HO2S sensors Figures and 3 are checked for proper output voltage and response rate the time it takes to switch from lean to rich or rich to lean Downstream HO2S sensors Figures 1 and 3 used for Catalyst Monitor are also monitored for proper output voltage Input is reguired from the ECT or CHT IAT MAF TP and CKP sensors to activate the H025 Monitor The Fuel System Monitor and Misfire Detection Monitor must also have completed successfully before the HO2S Monitor is enabled The HO2S sensor senses the oxygen content in the exhaust flow and outputs a voltage between zero and 1 0 volt Lean of stoichiometric air fuel ratio of approximately 14 7 1 for gasoline engines the HO2S will generate a voltage between zero and 0 45 volt Rich of stoichiometric the HO2S will generate a voltage between 0 45 and 1 0 volt The HO2S Monitor evaluates both the upstream Fuel Control and downstream Catalyst Monitor HO2S for proper function Once the HO2S Monitor is enabled the upstream H025 signal voltage amplitude and response frequency are checked Excessive voltage is determined by comparing the HO2S signal voltage to a maximum calibratable threshold voltage A fixed frequency closed loop fuel control routine is executed and the upstream HO
18. nction nor its diagnosis for faults Always verify the vehicle concern then perform the pinpoint diagnostics from the appropriate PC ED Service Manual 3 Diagnosing lean conditions and lean DTCs P0171 P0174 Freeze Frame Data can often help to identify the type of lean condition even if the fault is intermittent by indicating how the vehicle was being driven when the fault occurred Diagnosis of lean conditions and lean adaptive DTCs can be difficult especially if the concern is intermittent Verifying the concern is extremely important There are different types of lean conditions The ability to identify the type of lean condition causing the concern can be crucial to a correct diagnosis When DTCs P0171 and P0174 are both present there is a strong likelihood of another concern being present a Vacuum leaks unmetered air In this type of condition the engine may actually run lean of stoichiometry 14 7 1 air fuel ratio if the PCM is not able to compensate enough to correct for the condition This condition is typically caused by air entering the engine through an abnormal source opening or due to a MAF malfunction In this situation the volume of air entering the engine is actually greater than what the MAF is indicating to the PCM Vacuum leaks will normally be most apparent when high manifold vacuum is present during idle or light throttle If Freeze Frame Data indicates that the fault occurred at idle a check for vacuum leaks unmetered
19. rs The Monitor then observes the switching frequency and compares it to a threshold frequency stored in an rpm load table A frequency higher than the maximum calibrated threshold indicates a malfunction The Catalyst Monitor DTCs can be categorized as follows Catalyst system efficiency below threshold Bank 1 P0420 Catalyst system efficiency below threshold Bank 2 P0430 CATALYST EFFICIENCY MONITOR Diagnosi Take Code __Desorpon Posle Causes P0420 Catalyst System Efficiency Indicates Bank 1 catalyst system eMalfunctioning ECT CHT Below Threshold Bank 1 efficiency is below the acceptable threshold High fuel pressure Damaged exhaust manifold Cylinder misfiring HO2S wiring concerns shorted or chafed bent pins etc Damaged exhaust system pipe Damaged mutfler ta pipe assembly Retarded spark timing Damaged Catalytic Converter Use of leaded fuel Oil contamination consumption Silicone contamination sealamts cleaners P0430 Catalyst System Efficiency Same as DTC P0420 but opposite See Possible Causes for DTC P0420 Below Threshold Bank 2 D2 Catalyst Efficiency Monitor Diagnostic Trouble Codes Article No 01 9 7 Emissions Engine Controls Driveability Diagnosis E FUEL SYSTEM MONITOR El Fuel System Monitor Information The Fuel System Monitor is an on board strategy designed to monitor the fuel trim system The fuel control system uses f
20. t the PCM will once again have to adapt back to the normal operating conditions Clearing the KAM will erase what the PCM has learned so the PCM will be able to start with base tables 2 Always view and record Freeze Frame Data Freeze Frame Data can be a valuable asset in duplicating and diagnosing concerns This data a snapshot of certain PID values recorded at the time the MIL was activated indicates the manner in which the vehicle was being driven at the time the fault occurred This can be especially useful on intermittent concerns Freeze Frame Data in some cases can also help to isolate possible areas of concern as well as ruling out others Always record write down the Freeze Frame Data 3 Multiple DTCs with the same meaning When multiple paired DTCs with the same meaning are set for multiple sensors it is unlikely that replacing both HO2S sensors will resolve the concern In most cases there will be another issue that is causing the codes Examples of multiple paired DTCs P0135 P0155 P0141 P0161 P1131 P1151 P1132 P1152 To further clarify this see the more detailed scenario as follows A vehicle comes in with a MIL On concern KOEO self test reveals DTCs P0135 and P0155 HTR 11 and HTR 21 circuit malfunction with no other DTCs present The most likely cause of these DTCs would be something in the heater power circuit that both of these HO2S sensors have in common Example open or shorted heater cir
21. that the unused HO2S sensor PIDs display 0 volts 5 H025 sensors measure oxygen in the exhaust not fuel The exhaust gas condition reported by the HO2S sensor is based on the presence of oxygen in the exhaust not the presence of unburned fuel Example In the event of an ignition related misfire you might expect a rich HO2S reading due to the amount of unburned fuel in the exhaust system However there is also a large amount of unburned oxygen since no combustion took place in the misfiring cylinder Since the H025 senses oxygen only it would report a lean condition in this particular situation F2 Tips Related to Heated Oxygen Sensor H025 Monitor 1 OBD II Response Rate Monitor The OBD II Response Rate Monitor P0133 P0153 is only run at vehicle speeds between approximately 50 95 km h 30 60 mph during steady state conditions The test lasts approximately 6 seconds Therefore PO133 P0153 cannot be diagnosed at idle in the repair bay 2 Do not compare H025 switch rate Bank to Bank or vehicle to vehicle Different H025 switch rates from Bank to Bank are considered normal The H025 switch rate from one Bank to the other should not be compared as a gauge of the H025 s ability to switch react The PCM is continuously adjusting spark and fuel in reaction to engine operating conditions rpm load air flow throttle angle etc The PCM is also continuously adapting to certain conditions customer driving habits engine and
22. uel trim tables stored in the PCM s KAM to compensate for variability in fuel system components due to normal wear and aging Fuel trim tables are based on vehicle speed and engine load During closed loop vehicle operation the fuel trim strategy learns the corrections needed to correct a biased rich or lean fuel system The correction is stored in the fuel trim tables The fuel trim has two means of adapting a LONGFT and a SHRTFT LONGFT relies on the fuel trim tables and SHRTFT refers to the desired air fuel ratio parameter LAMBSE LAMBSE is calculated by the PCM from HO2S inputs and helps maintain a 14 7 1 air fuel ratio during closed loop operation SHRTFT and LONGFT work together If the HO2S indicates the engine is running rich the PCM will correct the rich condition by moving SHRTFT in the negative range less fuel to correct for a rich combustion If after a certain amount of time SHRTFT is still compensating for a rich condition the PCM learns this and moves LONGFT into the negative range to compensate and allows SHRTFT to return to a value near 0 Input from the ECT or CHT IAT and MAF sensors is required to activate the fuel trim system which in turn activates the Fuel System Monitor Once activated the Fuel System Monitor looks for the fuel trim tables to reach the adaptive clip adaptive limit and LAMBSE to exceed a calibrated limit The Fuel System Monitor will store the appropriate DTC when a fault is detected as described below
23. wertrain Control Emissions Diagnosis PC ED Workshop Manual pinpoint tests The pinpoint tests in the PC ED Manual should ALWAYS be followed when diagnosing vehicle conditions ACTION Use the following information and Service Tips to assist in the diagnosis of H025 Catalyst and Fuel System Monitor related DTCs OTHER APPLICABLE ARTICLES 98 23 10 WARRANTY STATUS INFORMATION ONLY OASIS CODES 623000 690000 698298 Article No 01 9 7 Emissions Engine Controls Driveability Diagnosis INFORMATION A Description of Terms and Acronyms B HO2S Location Diagrams C Heated Oxygen Sensor HO2S Monitor Cl Heated Oxygen Sensor HO2S Monitor Information C2 Heated Oxygen Sensor HO2S Monitor Diagnostic Trouble Codes DTCs D Catalyst Efficiency Monitor D1 Catalyst Efficiency Monitor Information D2 Catalyst Efficiency Monitor Diagnostic Trouble Codes DTCs E Fuel System Monitor El Fuel System Monitor Information E2 Fuel System Monitor Diagnostic Trouble Codes DTCs F Diagnostic Service Tips Fl Tips General F2 Tips Related to Heated Oxygen Sensor HO2S Monitor F3 Tips Related to Catalyst Monitor F4 Tips Related to Fuel System Monitor Article No 01 9 7 Emissions Engine Controls Driveability Diagnosis A DESCRIPTION OF TERMS AND ACRONYMS CHT Cylinder Head Temperature Sensor or PID CKP Crankshaft Position Sensor or PID DTC Diagnostic Trouble Code ECT
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