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Contents
1. LEFT FRONT RIGHT REAR ABS 2E SYSTEM DESCRIPTION ABS Operating Modes To illustrate the functioning of the four operating modes of this ABS system the next four pages show the system diagram with the mechanical valve in the appropriate position for each mode For clarity we assume that the ECU is operating only the solenoid for the right rear brake circuit Recall that this circuit also effects the left rear brake circuit through the mechanical valve Normat BRAKING Driver depressing pedal ECU passive monitoring e Zero current in solenoid valves Pump off Plunger piston full right pressure port open Master cylinder pressure supplied to all wheel cylinders ABS 2E SYSTEM DESCRIPTION Pressure REDUCE Pump pressure raising pedal ECUcontrolling solenoid valves and pump Full current in the right rear solenoid valve Pump running e Plunger piston moves left closes pressure port system balances the two rear wheel cylinders ABS 2E SYSTEM DESCRIPTION Pressure Hold cl L Pressure Hop Pedal firm ECU controlling solenoid valves and pump e Hat current in the right rear solenoid valve Pump Off Pressure port closed Plunger piston is stationary m2. T6E0 Faulty tone wheel etc T6FO Faulty solenoid valve circuit s in hydraulic unit Front right wheel control Front left wheel control Partial list of Trouble Codes From 1992 Legacy Service Manual 15 ABS 2E PROCEDURES Air Bleeding OVERVIEW The air bleeding procedure for the ABS 2E system is similar to that used for other systems with a few added steps Refer to the Service Manual for general rules and step by step instructions As always pay attention to the basics Before you begin make certain there are no leaks in the system Then bleed the secondary chamber of the master cylinder first and the primary chamber second To accomplish this work in the following order 1 Right front brake 2 Left rear brake 3 Left front brake 4 Right rear brake PEDAL TRAVEL MEASUREMENT To properly perform the following procedure you will need a pedal effort gauge SOA 636500 With all four brake circuits bled check pedal travel as follows 1 Put the wheel in a convenient position 2 With the engine idling use the pedal effort gauge to apply 110 pounds of load to the brake pedal 3 Measure the distance between the brake pedal and the rim of the steering wheel 4 Release the brake pedal and take the same measurement TIP Tie one end of a length of string to the brake pedal Press the brake pedal and at the opposite end of the string place a paper clip to ma
3. SUBARL INTRODUCTION TO ABS 2E SYSTEM DIAGNOSIS Video Reference Booklet Subaru of America Inc Copyright 1992 Subaru of America Inc All rights reserved This book may not be reproduced in whole or in part without the express written permission of Subaru of America Inc Subaru of America Inc reserves the right at any time to make changes or modifications to systems procedures descriptions and illustrations contained in this book without necessarily updating this document Information herein is considered current as of December 1992 MSASAV141B CONTENTS Foreword System Description OVOIVIOW Tm 1 ABS 2E System Differences ABS Operating Modes The Mechanical Valve Chambers amp Connections Moving the Plunger Piston Damping Oscillations ABS Operating Modes Normal Braking Mode Pressure Reduce Mode Pressure Hold Mode Pressure Increase Mode ANEREN Diagnostics ABS Self Diagnostics Displaying Codes Interpreting Codes Self Tests Clearing Codes Troubleshooting Process Basic Checks Self Diagnosis Ss Trouble Codes neret annuo te bonn akna naar nnde teta tata Procedures Air Bleeding Overview Pedal Travel Measurement Sequence Control HCU Pressure Check Overview Setting Up a Pressure Gauge Pressure Tables Conclusion FOREWORD This Video Reference Bookl
4. condition once three codes are in memory the newly arriving code displaces the oldest stored code The newest code takes the first place in line for display CLEARING CODES To clear the memory of all stored codes alternately disconnect and reconnect the jumper between ground and terminal L in the ABS check connector Do this three times in the span of about 12 seconds TIP At the moment the ECU clears its memory you can hear the relays in the HCU cycle once Troubleshooting Process To troubleshoot ABS systems it s best to follow a step by step procedure like the one on page 31 of the 1992 Legacy ABS 2E Service Manual Supplement Three Fault Codes Stored in Memory Refer to the Service Manual for Diagnostic Information ABS 2E DIAGNOSTICS Enter the flow diagram with the symptom reported on the repair order The diagram calls that Trouble Occurs The first step in the procedure is Basic Checks This calls for a visual inspection to look for obvious problems and includes the following items improper battery voltage low brake fluid level brake fluid leaks brake drag condition of the brake pads and rotors Size type and condition of the tires Checking for Brake Drag Checking Brake Fluid Level Notes ABS 2E DIAGNOSTICS Check the tires to confirm that they are the correct tires for the vehicle that they are in good co
5. union You should be able to find the brake tubing and the connecting parts at most auto parts stores For the pressure gauge itself check industrial supply houses Follow these steps to assemble the parts 1 Cut each of the two 8 steel brake lines in half to remove one of the fittings on each line Join the two cut ends with the 3 16 compression union Connect the pressure gauge to the 1 4 NPT to 1 8 NPT reducer use Teflon tape Connect the 3 16 inverted flare to 1 8 NPT to the reducer use Teflon tape Connect the 5 16 flare fitting to the gauge assembly the 10 x 1 0 mm fitting will connect to the HCU TIP When the tester is not in use put a rubber cap from a bleeder screw over the open fitting to keep dirt out 18 ABS 2E PROCEDURES PRESSURE GAUGE 1 4 NPT TO 1 8 NPT REDUCER 3 16 FITTING Doing an HCU Pressure Check 3 16 INVERTED 3 16 STEEL FLARE TO 1 8 NPT BRAKE LINE 3 16 TO 3 16 COMPRESSION UNION 3 16 STEEL 10MM X 1 0 BRAKE LINE FITTING E HCU Pressure Check Set up 19 ABS 2E PROCEDURES DESCRIPTION When Sequence Control starts the left front Solenoid cycles first then the right front solenoid and finally the right rear As the right rear solenoid works pressure in the left rear brake circuit is simultaneously regulated by the mechanical valve It is not necessary to exactly match the
6. values in the pressure table during your tests The important thing is that you observe the sequence shown in the table below 1 INTITAL VALUE the hydraulic circuit pressurizes as you press the brake pedal 2 WHEN DECOMPRESSED the circuit automatically loses pressure as the HCU cycles the solenoid valve to pressure reduce mode 3 WHEN COMPRESSED the circuit regains pressure at least equal to the initial reading as the system returns to pressure increase mode When When FrontBrakes Brakes 498 psi 3 432 kPa 71 psi 490 kPa 498 498 psi 3 432 kPa 3 432 498 psi 3 432 kPa 498 psi 3 432 kPa 71 psi 490 kPa 498 psi 3 432 kPa Normal pressure readings The pressure check is repeated for each of the four HCU pressure output ports Recall that three of the brake hydraulic circuits are controlled by solenoid valves all but the left rear circuit If a check of any one of these circuits yields incorrect pressure readings this may indicate a non functioning solenoid valve CIRCUIT Initial Value 498 psi 3 432 kPa 498 psi 3 432 kPa Typical incorrect readings are shown in the two tables below In the first example the pressure does not decrease from the initial value In the second example the pressure fails to reach the initial value at the start of Sequence Control When Decompressed When Compressed 498 psi 3 432 kPa Example 1 Pressure does not decrease
7. aintains reduced pressure in the right and left rear wheel circuits ABS 2E SYSTEM DESCRIPTION Pressure n Increase Mode PRESSURE INCREASE Driver pressing pedal pedal falling Zero current in solenoid valves Pump off Master cylinder pressure applied to right rear wheel circuit raises pressure Plunger piston begins to move right opens pressure port master cylinder pressure drives plunger piston full right Full master cylinder pressure applied to the left and right wheel cylinders NOTE If necessary the ECU cycles each brake circuit through the various ABS modes as required to control wheel lock up ABS 2E DIAGNOSTICS ABS Self Diagnostics The ABS 2E electronic control unit or ECU can store up to three trouble codes in its memory It does this whenever it detects an out of range signal in any of its inputs When a fault condition is active the ECU goes into fail safe mode and turns on the ABS warning lamp The brake system then functions only in conventional mode If the fault condition is caused by an intermittent problem the ABS warning lamp may go off at the next ignition switch ON OFF cycle but the code will still be stored in the ECU s memory DisPLAviNG Copes To display any stored codes use the following procedure 1 Remove the small kick panel on the lower driver s door A pillar 2 Enter ABS s
8. dition it goes into fail safe mode and turns on the ABS warning lamp In fail safe mode the ABS system is essentially shut down and completely passive while the brake system operates conventionally The system remains in fail safe mode until the ignition switch is turned to OFF The next time the ignition switch is turned to ON the ECU again initializes and looks for fault conditions first at key ON and again after 20 seconds at 6 miles per hour or more If the fault condition is still there the ECU simply returns to fail safe mode NOTE Even though the ECU can store up to three codes this can happen only if at least two of the fault conditions are intermittent This means the ECU stays in fail safe mode as long as the first fault condition remains in effect and will neither detect nor store in memory any additional fault conditions If the first fault condition clears the ECU again exercises active ABS control at the next key ON One Fault Code Stored in Memory If a second fault condition occurs the ECU will then store the second code Two Fault Codes Stored in Memory ABS 2E DIAGNOSTICS To get a third code into memory the second fault condition must also be intermittent When it clears the ECU can come out of fail safe mode at the next ignition ON OFF cycle At that point the ECU can detect then store the third code If the ECU detects another fault
9. e Be prepared to press on the brake pedal with considerable effort for the duration of the check To perform an HCU pressure check follow these steps 1 At the HCU loosen the hydraulic fluid pipe for the left front brake circuit In its place attach a suitable pressure gauge 3 Bleed air from the pressure gauge 4 Activate the Sequence Control mode Observe the pressure gauge as the system cycles the left front solenoid valve through pressure reduce pressure hold and pressure increase Compare the readings to the values in the table Move the pressure gauge to the right front brake circuit connection at the HCU and reconnect the previously disconnected pipe Then repeat Steps 3 through 5 Repeat these steps for the two remaining HCU ports left and right rear When you have finished these checks make sure all of the brake fluid pipe connections are secure and free from leaks and that the System is bled properly 2 4 21 ABS 2E PROCEDURES Conclusion Effective diagnosis of the ABS 2E system depends on a logical step by step approach When you troubleshoot an ABS 2E system use the appropriate service manual follow the procedures and do not skip any steps As always pay attention to the basics Use the instructions in the service manual and in this VRB to look for fault codes perform diagnostics and properly bleed air from the system When appropriate use the HCU pressu
10. e independently in any of three pressure modes These are pressure reduce pressure hold and pressure increase These modes are related to the amount of current flowing through the solenoid valve as determined by the ABS ECU NOTE Theterm pressure increase may suggest that the HCU raises pressure above that achieved by pressing the brake pedal This is not the case Full Current ABS Pressure Reduce To From Wheel X Master Oylinder Cylinder To Reservoir Half Current ABS Pressure Hold To From Wheel X X Master Cylinder Cylinder X l To Reservoir No Current Conventional Braking or ABS Pressure Increase To From Wheel Master Cylinder Cylinder X To Reservoir Solenoid Valve Function Diagram ABS 2E SYSTEM DESCRIPTION The Mechanical Valve In the ABS 2E hydraulic control unit the fourth solenoid valve has been replaced by a mechanical valve containing a plunger piston This mechanical valve controls the left rear hydraulic brake circuit CHAMBERS amp CONNECTIONS In the right side of the valve is a pressure equalization chamber The head of the plunger piston divides this chamber in half zones A and B in the diagram If pressure in both halves of the chamber is equal spring tension keeps the plunger piston in the home position all the way to the right The right half of the chamber is connected to the master cylinder port 2 and to the pump in the HCU port 6 The l
11. eft half of the pressure chamber is connected to the right rear hydraulic circuit port 5 During conventional braking the master cylinder pressurizes both sides of this chamber However if pressure in the left half of the chamber is lower than pressure in the right half the plunger piston is allowed to move to the left E Pressure p Piston2 Port Pushrod Mechanical Valve Components The other side of the mechanical valve contains a passage zone E One end of this passage is connected to the master cylinder port 1 the other side is connected to the pump port 3 The passage is also connected through a pressure port to a second pressure chamber zone D This chamber is connected to the left rear hydraulic brake circuit port 4 Also in this chamber is a second piston piston 2 Piston 2 is connected to the plunger piston by means of a pushrod B Plunger Piston ABS 2E SYSTEM DESCRIPTION MoviNG THE PLUNGER PISTON When the system puts the right rear hydraulic circuit in pressure reduce mode the solenoid valve in that circuit closes the inlet and opens the outlet Wheel cylinder pressure is then reduced because brake fluid is allowed to bleed back to the reservoir in the HCU Through port 5 there is a hydraulic connection between the wheel cylinder circuit and the left half of the pressure chamber zone B With wheel cylinder pressure reduced pressure acting on the left side
12. et accompanies the Introduction to ABS 2E System Diagnosis videotape The booklet summarizes information in the videotape and provides additional information for a number of subjects including air bleeding and a pressure test procedure for the hydraulic control unit In addition to this booklet and videotape we recommend that you use the Impreza and Legacy Service Manuals as well as any other appropriate materials to help you perform effective diagnosis and repair of the ABS 2E system ABS 2E SYSTEM DESCRIPTION Overview In the past Subaru vehicles have been fitted with either of two anti lock braking systems one is a Robert Bosch unit the other is the ABS 2SL system from Nippon ABS Limited Now there is a new anti lock braking system manufactured for Subaru by Nippon ABS Limited The new Nippon system is designated ABS 2E This system uses ABS components also found in previous anti lock braking systems These are as follows e 4 tone wheels 4 wheel speed sensors hydraulic control unit HCU electronic control unit ECU ABS warning light The HCU incorporates two relays three solenoid valves a mechanical valve and a fluid pump and motor NOTE TheService Manual refers to the solenoid valves in the HCU as magnet valves In the ABS 2E videotape and in this VRB we use solenoid valve because it is a name more commonly used in the U S market Like its predecessors ABS 2E is a four
13. ified a specific trouble code the Basic Troubleshooting Procedure tells you what to do next 1 Follow the troubleshooting steps in the chart 2 Make the necessary repair 3 Clear the memory 4 Repeat the self diagnostic check Trouble Code Refer to Checking a Wheel Speed Sensor Circuit In all cases road test the vehicle when the preceding steps are done This is necessary because some codes will not set until vehicle Speed has been driven at six miles per hour or more for at least 20 seconds NOTE Do NOT substitute spinning the wheels on the service lift for a road test On FWD vehicles this can cause the ECU to incorrectly set a fault code Contents of diagnosis 0 Warning light OFF TeA0 Trouble in the warning light drive circuit Warning light is not on for 1 5 seconds after ignition switch is on 0 Remi ON or TeBo rouble code output Trouble in the warning light drive circuit Start code 1 a Trouble code is shown after start code b Only start code is shown in normal condition 21 Faulty ABS sensor Deco Open circuit or input voltage excessive Front right wheel sensor Front left wheel sensor Rear right wheel sensor Rear left wheel sensor Faulty ABS sensor T DO input When there is no open circuit or speed signal Front right wheel sensor Front left wheel sensor Rear right wheel sensor Rear left wheel sensor
14. may indicate faulty solenoid valve CIRCUIT Initial Value ANY Less than 498 psi 3 432 kPa When Decompressed When Compressed Less than 71 psi 490 kPa 498 psi 3 432 kPa Example 2 Pressure does not reach initial value at start of Sequence Control 20 ABS 2E PROCEDURES The third example shows the readings for the right rear circuit are correct but the readings in the left rear circuit do not change from the initial reading this may indicate a malfunction in the HCU s mechanical valve ni When When CIRCUIT Initial Value Decompressed Compressed Right Rear 498 psi 3 432 kPa 71 psi 490 kPa 498 psi 3 432 kPa Left Rear 498 psi 3 432 kPa 498 psi 3 432 kPa 498 psi 3 432 kPa Example 3 Pressure values for right rear circuit are correct but left rear pressure does not decrease CAUTION For this check use a pressure gauge that is reserved exclusively for brake fluid Do NOT use a gauge that has been used for transmission pressure tests doing so could lead to brake system malfunctions NOTE Before you start the HCU pressure checks pump the brake pedal several times That will bleed vacuum from the vacuum booster so that it is at atmospheric pressure NOTE This check requires that you press on the brake pedal so that the pressure gauge displays a pressure equal to or more than the initial value in the tabl
15. ndition and that they are inflated to the correct pressure If you find something wrong at this stage correct it and see if it eliminates the reported symptom If not continue to Step 3 Step 3 is Self diagnosis At this time put the ECU into self diagnostic mode and monitor the ABS warning lamp for trouble codes If the lamp functions properly and there are no trouble codes stored you will see a continuously flashing Code 11 In that case go to the General Troubleshooting Chart There you will find separate procedures for the following symptoms brake pedal vibration and noise excessive stopping distance too much or too little pedal travel inoperative ABS system frequent ABS operation X Checking Inflation Pressure ABS 2E DIAGNOSTICS Proceed to Step 4 in the diagram if the ECU has stored one or more codes or if the ABS warning lamp is malfunctioning Step 4 directs you to troubleshoot in accordance with trouble code That means turn to Section T6 and look for the specific chart that matches the trouble code you recorded There is a chart in Section T6 to cover every possible ABS trouble code A table lists all of the codes tells you where to look for diagnostic information and summarizes the reason for the trouble code Notice that in some cases you have to look all the way over to the right column to find out to which component a specific trouble code refers Once you ve ident
16. of the plunger piston is also reduced Master cylinder pressure acting on the right side of the plunger piston zone A now overcomes spring tension and begins to move the plunger piston to the left As the plunger piston moves the push rod causes piston 2 to move along with it As piston 2 moves to the left it first closes the pressure port to isolate the left rear wheel cylinder port 4 from master cylinder pressure port 1 As piston 2 moves farther to the left it exposes the left rear wheel cylinder port 4 to the right side of the second chamber zone D As piston 2 continues to move to the left the expanding volume in the second chamber decreases pressure in the left rear hydraulic circuit When the system once again allows pressure to increase in the right rear hydraulic circuit pressure in zone B moves the plunger piston back to the right In actual practice this process of moving the piston happens very quickly and repeats many times per second as the system cycles DAMPING OSCILLATIONS An additional benefit of this arrangement is hat the mechanical valve damps out some of he unwanted oscillation in the brake pedal as the ABS pump runs Because of this the F valve used on the ABS 2SL system is no onger needed and has been eliminated from the circuit MASTER HYDRAULIC CONTROL UNIT SOLENOID VALVE 1 Bon eae Sor Soc SOLENOID VALVES St
17. r reservoir after bleeding each circuit Then road test the vehicle at low speed Apply the brakes hard two or three times to make sure that the brakes are working properly 17 Pedal Effort Gauge SOA 636500 Adding Brake Fluid to the Reservoir ABS 2E PROCEDURES HCU Pressure Check OVERVIEW It is possible to check the operation of the hydraulic control unit using a hydraulic pressure gauge To do this you connect the gauge to one of the pressure output ports of the HCU then start Sequence Control As you start Sequence Control press the pedal so that a specified initial pressure shows on the pressure gauge This initial pressure is shown in the table on page 20 Once Sequence Control starts the ECU cycles the solenoid valves so that each brake circuit decompresses pressure reduce mode and re compresses pressure increase mode As this happens the reading on the pressure gauge should decrease to 71 psi or less then come back to 498 psi or more Settine Up A PRESSURE GAUGE To build a set up for checking HCU pressures you will need the following parts pressure gauge 1 500 or 2 000 psi 3 16 steel brake line 8 long with 5 16 flare fittings Gibson PN 308CK e 3 16 steel brake line 8 long with 10 x 1 0 mm flare fittings Gibson PN 308MJ 1 4 NPT to 1 8 NPT reducer Edelman PN 219420 3 16 inverted flare to 1 8 NPT Edelman PN 124320 3 16 to 3 16 compression
18. re check to test the functioning of the three solenoid valves and the mechanical valve 22 ABS 2E PROCEDURES NOTES
19. rk the first distance Then release the brake pedal and place a second paper clip to mark the second distance Measure between the two paper clips with a ruler or tape measure Bleed the Secondary Chamber First Pedal Effort Gauge Measures Force Measuring Brake Pedal Travel 16 ABS 2E PROCEDURES The difference between the two distances pedal depressed pedal released must be less than 3 75 inches 95 mm If it is greater than that there is air trapped in the HCU Expel this air using Sequence Control explained in the next section of this VRB SEQUENCE CONTROL Sequence Control is the name of a mode in which the system automatically runs the HCU pump motor and cycles the solenoid valves The Sequence Control actions help to purge air out of the hydraulic control unit To activate Sequence Control proceed as follows 1 With the ignition off jumper both the L and K terminals in the ABS check connector to ground 2 Turn the ignition switch to ON and watch the ABS warning lamp 3 When the lamp goes off immediately press and hold the brake pedal 4 The ECU now runs the pump and cycles all of the solenoid valves You will hear and feel this happening 5 When you hear the pump stop you know Sequence Control is done Release the brake pedal and turn the ignition to OFF When you have completed Sequence Control bleed all four brake circuits again Top off the master cylinde
20. sensor four channel system However it is smaller and lighter than the earlier designs In addition the ABS 2E system incorporates improvements in the areas of trouble code memory self diagnostics inspection and maintenance The ABS 2E system will appear in production with the start of the 1993 model year It will be available on the Legacy model if equipped with an automatic transmission Also every Impreza that has anti lock braking will be fitted with the ABS 2E system Subaru ABS Hyaraulic Control Units An ABS Wheel Speed Sensor and Tone Wheel ABS 2E SYSTEM DESCRIPTION ABS 2E System Differences The ABS 2E system differs from the earlier ABS designs in four ways 1 Earlier designs used four solenoid valves The ABS 2E hydraulic control unit HCU uses three solenoid valves and one mechanical valve 2 Its electronic control unit can store up to three trouble codes rather than just one 3 The number of separate error conditions the ECU can recognize has been increased That means there are more trouble codes available gt C 4 There is a revised bleeding procedure ABS 2E Hydraulic Control Unit Notes ABS 2E SYSTEM DESCRIPTION ABS Operating Modes During anti lock braking the HCU operates one or more of the solenoid valves to control the hydraulic pressure acting on the brakes Each solenoid valve can operat
21. ystem diagnostic mode by jumpering terminal L in the ABS check connector to body ground Check the schematic in the service manual to identify terminal L Note Some models have a grounding lead attached to the check connector Turn the ignition switch to ON Observe the ABS warning lamp It will begin to flash out one or more codes When you enter diagnostic mode the ECU displays the newest code first then the second code and then the oldest 3 4 Removing the Trim Panel ABS Warning Lamp 10 ABS 2E DIAGNOSTICS Each code display cycle begins with the start code eleven After code 11 the ECU displays any stored trouble codes When you see code 11 again you know the ECU is repeating the cycle INTERPRETING CODES Each code is made up of long and short flashes just like those used by the fuel system Count each long flash as 10 each short flash as one For example if the lamp flashes one long and one short that represents code 11 If it flashes two long and one short that is code 21 Sg F TEsTS Each time the ignition switch is turned from OFF to ON the self diagnostic function begins to look for fault conditions These self tests occur in two stages one at key ON and another as soon as the vehicle has been driven at a speed of 6 miles per hour or more for 20 seconds Assume that a particular vehicle has no ABS codes stored If the ECU detects a fault con
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