Description of On-Board Diagnostics

Anti-lock brake system (ABS), self-diagnosis

The ABS control unit (Part No.357 907 379) has a permanent Fault memory. If problems occur at electrically monitored sensors or components they are stored in memory. Faults which occur occasionally are stored as sporadic faults.

Faults are stored with varying priorities: solenoid faults have the highest priority and are displayed first. Sporadic faults have the lowest priority and are displayed last.

If a fault is stored, the ABS indicator light (K 147) on the instrument panel will light up and, depending on the priority of the fault, ABS operation will be automatically switched off. The conventional braking system remains operational.

A check sequence is performed by the ABS control unit (J 104) after the engine is started and the hydraulic pump builds up pressure in the accumulator. The ABS warning light will come on during this check but remains on only if a fault is present.

The self-diagnosis must be initiated and the stored fault called up with the VAG 1551 tester. The VAG 1551 tester can access the ABS control unit memory via remote diagnostic terminals under the shift lever boot. Fault information must then be compared with the fault table/blink code in and the correct repair action taken.