Component Tests and General Diagnostics
The following procedure applies to cars from 1988 on and should be carried out if the ABS lamp lights while driving.Note: First. Fault Descriptions
Special tools: Multimeter, P/N 9996525-3, or voltmeter, P/N 9996450-4, and ohmmeter, P/N 9999724-9.
General
These fault-tracing instructions assume that the braking system as a whole is operational.
Important
The instructions on this and the following pages must be observed at all times, otherwise the control module may be damaged.
Control module monitoring circuit
The control module incorporates a fault-monitoring circuit designed to detect faults in the module itself, and in the sensor circuitry, hydraulic modulator, signal circuits etc.
On detecting a fault, the circuit disengages the ABS system and operates the warning lamp on the combined instrument. The following checks should be carried out if the lamp lights:
Note: All checks must be carried out
1. Battery:
- do not disconnect battery while engine is running
- disconnect battery leads when booster charging
- do not use booster charger or voltage source higher than 16 V for jump starting
2. Ignition
- Switch off ignition when disconnecting or connecting control module connector.
3. Control module
- Remove control module, for example when stoving paint work. The module must not be exposed to temperatures above +80°C (1 76°F).
- Disconnect control module connector when carrying out arc welding on the car.
- Do not replace module without checking associated wiring and components, otherwise new module may be damaged in same manner as original.
4. Check transient surge protector fuse (10 A)
- Remove sound proofing panel under dashboard on driver's side.
5. Check all ABS system connectors, wiring and ground terminals
- Ensure that components are correctly and securely connected.
- Poor contacts can cause fault symptoms.
Checking components and wiring
- See appropriate wiring diagram.
6. Switch off ignition
7. Disconnect control module connector
- Depress catch and lift off connector.
8. Remove protective cover from hydraulic modulator
9. Remove protective cover from connector
- Never insert test instrument probes into terminal sockets.
- Experience has shown that this may damage terminals and further aggravate fault(s).
- Check terminals through holes in connector sides. Do not exert greater force than necessary to make contact.
10. Remove white cover strips on connector sides
11. Check ground terminals in connector
12. Connect ohmmeter between ground and
- terminal 10
- terminal 20
- terminal 32
- terminal 34
- Resistance should be 0 ohm in all cases.
- If reading is incorrect: Check integrity and connection of leads.
- Leads are grounded at left-hand A-post.
- It test of terminal 32 indicates fault, repeat test with new valve relay. Relay is mounted on hydraulic modulator.
1. Valve relay
2. Motor relay
3. Connector
13. Switch on ignition
14. Check supply to transient surge protector
- Protector is mounted on bracket beside control module. First connect voltmeter between ground and terminal 1 on control module connector. Instrument should indicate battery voltage.
- If no voltage is present, measure directly at surge protector connector.
- Voltage should be present at terminals 1, 2 and 4. Also check that terminal 3 is grounded. If voltage is present at terminals 1 and 4 only when terminal 3 is grounded, surge protector is faulty and must be replaced.
- Note, battery voltage should be present at surge protector terminal 1 at all times, even when ignition is switched off and control module connector is connected.
15. Check converter unit
(Installed only on cars up to 1988.)
- Unit is mounted on control module bracket.
- Connect voltmeter between ground and terminals 7 and 9 on control module connector.
- Instrument should indicate battery voltage.
- If no voltage is present, measure directly at converter unit terminals 1, 2 and 4.
- If no voltage is present at any of above terminals, replace converter unit.
- Note, battery voltage should be present only at converter unit terminal 3 when control module connector is connected and ignition is on.
16. Check supply to control module connector
17. Connect voltmeter between ground and
- terminal 25, while operating brake pedal
- terminal 27
- terminal 28
- terminal 29. Note: Instrument should indicate 0.5-1.0 V. Instrument should indicate battery voltage in all cases except at terminal No.29.
- Start engine. Instrument should indicate battery voltage at terminal 15.
18. First check that wiring is intact. If voltage is not present at
- terminal 25: Check brake light switch and replace if necessary. Also check brake light bulbs and replace if necessary.
- terminal 27: Faulty valve relay. Replace relay.
- terminal 28: Faulty motor relay. Replace relay.
- Also measure at terminal 29. If voltage is present at terminal 27 when checked, instrument should indicate 0.5-1.0 V at terminal 29. If not, valve relay is faulty. Replace relay.
19. Switch off ignition
20. Check voltage at hydraulic modulator connector.
- Disconnect connector from unit
21. Switch on ignition
22. Connect voltmeter between ground and
up to 91 from 1992
- terminal 6 - terminal 6
- terminal 7 - terminal 11
- terminal 10 - terminal 8
- terminal 12 - terminal 10
- Instrument should indicate battery voltage in all cases.
23. If voltage is not present at above terminals, carry out following checks and ensure that wiring is intact:
- terminal 6: Check leads
- terminal 7: (Terminal 11 in models from 1992 on): Reconnect leads. ABS lamp should light. If not, replace lamp.
- terminal 10: (Terminal 8 in models from 1992 on): Surge protector faulty. Replace unit.
- terminal 12: (Terminal 10 in models from 1992 on):
- Check leads.
24. Switch off ignition
25. Reconnect connector
26. Check front sensors
- Connect ohmmeter to control module connector. Models to 1988 inclusive: Connect between terminals 4 and 6 for left front sensor, and between terminals 21 and 23 for right front sensor.
- Models from 1989 on: Connect between terminals 4 and 6 for left front sensor, and between 11 and 21 for right front sensor.
- Instrument should indicate between 0.9 and 2.2 kohm. If reading is incorrect: Measure at connectors at suspension strut towers in engine compartment. If reading is still incorrect; Check first that wiring is intact.
- If wiring is intact and reading is still incorrect: Replace sensor.
- Also inspect front sensor wheels for damage. Max. permissible radial run-out = 0.15 mm (0.006 in).
- Note, if replacing sensor wheel, ensure that correct type is installed:
- Models to 1988 inclusive: 96 teeth
- Models from 1989 on: 48 teeth.
27. Check rear sensor
- Connect ohmmeter between terminals 7 and 9. Instrument should indicate 0.6-1.6 kohm. If reading is incorrect: Measure at sensor connector located beside fuel filler pipe in luggage compartment.
- Note, connector seal must be replaced. If reading is still incorrect: Check first that wiring is intact.
- If wiring is intact and reading is still incorrect: Replace sensor.
- Sensor signals will be incorrect if sensor wheel is more than 0.2 mm Out of round or if any teeth are damaged. If so, replace sensor wheel.
- When replacing sensor wheel, remember that two different types (with 48 and 96 teeth) are available.
28. Checking sensor wiring
- Check that leads from control module connector are run to correct wheels. Connect ohmmeter as described in 26 and 27 'Check front/rear sensors'.
- Rotate left front, right front and rear wheels in turn, and connect probes to appropriate terminals. Resistance should vary as wheel rotates.
29. Check hydraulic modulator solenoid valves
- Connect one ohmmeter probe to terminal 32 on control module connector. Use other probe to measure at terminals 2 (left front), 35 (right front) and 18 (rear).
- Instrument should indicate 0.7-1.7 ohm in all cases. If reading is incorrect: Measure directly at hydraulic modulator (See wiring diagram). If reading is still incorrect: Replace modulator.
- Note, buzzer setting should be used when measuring low resistances with multimeter. Remember that resistance of instrument leads is included in reading.
30. Switch on ignition
31. Check motor relay in hydraulic modulator
- Connect jumper lead between ground and terminal 28.
- Hydraulic modulator should start.
- Note, do not connect lead for more than 2 seconds.
- Measure voltage between terminal 14 and ground while jumper lead is connected. Instrument should indicate battery voltage.
- If modulator does not start, check that wiring is intact. If fault persists, repeat test with new motor relay.
32. Check valve relay in hydraulic modulator
- Connect voltmeter between terminal 32 and ground. Connect jumper lead between ground and terminal 27. Valve relay should operate and instrument should indicate battery voltage.
- If relay does not operate, check that wiring is intact. It fault persists, repeat test with new relay.
33. Switch off ignition
34. Disconnect test equipment
- If no fault has been detected, repeat procedure with new control module.
35. Reinstall panels, carpets, hydraulic modulator cover etc