Component Tests and General Diagnostics
Fault tracing (checking) ABS brake systemThe instructions below should be followed in the event of the ABS warning lamp lighting up when vehicle is being driven.
Special tools:
Multimeter (Part No.999 6525-3) or voltmeter (Part No.999 6540-4)
and ohmmeter (Part No.999 9724-9).
General
These fault tracing instructions assume that the rest of the braking system is fully operational.
Important
Always follow instructions relating to the control unit, otherwise there is a risk of it being damaged beyond repair.
Control unit monitoring circuit
The control unit contains a circuit for fault monitoring. The function of the latter is to detect faults in the control unit, electrical faults in sensors, hydraulic modulator, signalling system, etc.
When the monitoring circuit detects a fault, it disengages the ABS system and lights up dashboard warning lamp. If lamp lights, carry out the following checks:
Note! All checks must be carried out
1. Check fuse in transient surge protector (10A)
- Remove soundproofing beneath dashboard on passenger side.
2. Check all connectors, wires and earth connections in ABS system
- Check that they are correctly connected and make good contact. Poor contact can give rise to a large number of symptoms.
Check components and wiring Use wiring diagrams. Electrical Diagrams
3. Turn off ignition
4. Lower control unit off bracket, loosen clamp
5. Remove connector from control unit
6. Remove hydraulic modulator protective cover
7. Remove connector protective cover
- Never check connections from front. Experience has shown that connections may be damaged and any fault made worse.
- Check connections through the holes in the side of the connector. Do not use more force than necessary. The numbers of the connections are stamped into the connector side.
8. Remove red cover strips on connector sides
9. Check connector earth connections
10. Connect an ohmmeter between earth and terminal: 10, 20, 32, 34
- The resistance should be 0 in all cases. If values are not 0, check that wires are undamaged and that they are correctly connected.
- The wires are earthed at the heater unit righthand support bracket below carpet.
- If a fault is found at terminal 32, first test with a new solenoid valve relay. The relay is mounted on the hydraulic modulator.
1. Solenoid valve relay
2. Pump motor relay
3. Connector
11. Switch on ignition
12. Check transient surge protector
- It is mounted on bracket next to control unit.
- Note, The connector should not be unplugged during metering.
- First connect a voltmeter between earth and terminal 1 on control unit connector.
- The meter should indicate normal battery voltage. If there is no voltage, measure directly on the transient surge protector connector. Terminals 1, 2 and 4 should be energized. Also check that terminal 3 is connected to earth. If only terminals 1 and 4 are energized when 3 is connected to earth, transient surge protector is defective and must be replaced.
13. Check converter
- The task of the converter is to convert ABS signals from the pulse wheel for the rear wheels to correct signals for the speedometer.
- The converter is mounted on the control unit bracket.
- Note, The connector should not be unplugged during measurement.
- Connect a voltmeter between earth and terminals 7 and 9 on the control unit connector.
- The meter should indicate normal battery voltage. If there is no voltage, measure directly on converter unit terminals 1, 2 and 4. If none of these terminals is energized, replace converter.
14. Check power supply to control unit connector
15. Connect a voltmeter between earth and:
- terminal 25. Depress brake pedal at the same time
- terminal 27
- terminal 28
- terminal 29. Note, the meter reading should be 0.5-1.0 V.
- The meter should indicate normal battery voltage at all terminals except No. 29. This reading should be 0.5-1.0 V.
- Start engine.
- The meter should indicate normal battery voltage at terminal 15.
16. First check that wires are intact If there is no voltage at:
- 25-check brake light switch, and any connector in the dashboard by the glove compartment (White 4-pole BL/R cable)
- 27-solenoid valve relay defective - replace it
- 28-pump motor relay defective - replace it
- 29- if voltage at terminal 27 is correct, voltage at terminal 29 should be 0.5-1.0 V.
17. Switch off ignition
18. Check voltage to hydraulic modulator connector. Disconnect connector from modulator
19. Switch on ignition. Connect a voltmeter between earth and terminals 6, 7, 10 and 12
- The voltmeter should indicate normal battery voltage.
20. If there is no voltage at terminals, carry out the following checks and also check that wires are intact:
- 6-check wires
- 7-fit connector. The ABS lamp should light up. If not, replace bulb
- 10-fault in transient surge protector - replace it
- 12-check wires.
21. Check earth cable between hydraulic modulator and earth:
- The cable is located behind battery. It must be undamaged and properly connected.
22. Switch off ignition
23. Fit connector to hydraulic modulator
24. Check front sensors
- Connect an ohmmeter to control unit connector.
- Bridge terminals 4 and 6 for the front left sensor and 11 and 21 for the front right sensor.
- The resistance should be between 0.9 and 2.2 kilo-Ohms. If other values are obtained, measure at connectors on suspension towers in engine compartment. If the value is still incorrect, first check that wires are not damaged.
- If the value remains incorrect, replace sensor. Also check front pulse wheels for any damage. Radial gap max. 0.15 mm, mounted on hub.
- Note, When replacing a pulse wheel, take care to install it correctly.
25. Check rear sensor
- Connect an ohmmeter across terminals 7 and 9. The resistance should be between 0.6 and 1.6 kilo-ohms. If other values are obtained, measure at sensor connector in the rear axle casing.
- Note, the connector seal must be broken. If the value is still incorrect, replace sensor.
- Note, if pulse wheel is out-of-round, has a gap greater than 0.2 mm, or has damaged teeth, it will give incorrect signals when the vehicle is being driven, and must be replaced.
26. Check running of wiring to sensors
- Check that wires have been run to the correct wheel, from control unit connector to sensors. Do this by connecting an ohmmeter in accordance with 24 and 25 above (check sensors).
- Rotate wheels, front left, front right, and rear, one at a time.
- Move ohmmeter to relevant terminals. The resistance will vary by 100-220 ohm when wheels rotate. This indicates that the sensor is functioning.
27. Check hydraulic modulator solenoid valves
- Connect one of ohmmeter test wires to terminal 32 on the control unit connector. Move the other test wire between terminals 2, 18 and 35. 2=FL, 35=FR and 18=rear.
- The measured values should be between 0.7 and 1.7 ohm. If other values are obtained, measure directly on the hydraulic modulator. Electrical Diagrams If an incorrect value is obtained, replace hydraulic modulator.
- Note, in measuring low resistances with a multi- meter, the buzzer position is to be used. Also bear in mind that the measurement also includes resistance in measuring cables.
28. Switch on ignition
29. Check motor relay in hydraulic modulator
- Connect a wire between earth and pin 28 on control unit connector. The hydraulic modulator should then start.
- Note, connect wire for 2 sec. only.
- At the same time, measure with a voltmeter across connector terminal 14 and earth. Battery voltage should be obtained.
- If the hydraulic modulator does not start, check that wiring is intact. If fault persists, test with a new motor relay.
30. Check valve relay in hydraulic modulator
- Connect a voltmeter between pin 32, on control unit connector, and earth. Connect a wire between earth and pin 27. The valve relay should then switch and the voltmeter should indicate battery voltage. If not, check that wires are not damaged. If fault persists, test with a new relay.
31. Switch off ignition
32. Disconnect test equipment
- If no fault is discovered in the course of fault tracing, test with a new control unit.
33. Restore
- Refit panels, cover above hydraulic modulator, etc.