Diagnostic Procedure: Preparation

WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 1989 Audi 90, 1989 Audi 80, 1989 Audi 200, 1989 Audi 100, and 1988 Audi 90. However, it is still accessible from the selected car via links, so may be relevant.

Test results are dependent on the correct operation of several related non-ABS components and systems. The following areas should be checked and corrected before attempting to diagnose ABS system.

Ensure that fuses No. 3 and 12 are okay. Make sure anti-lock brake system is turned on and that ground connection at hydraulic modulator is tight. Check connections at hydraulic modulator for leaks.
Ensure brake components (pads, rotors, etc.) are okay. On 5000CS Quattro, DO NOT engage differential locks unless specified. Check that fuse on anti-lock power supply relay (located on auxiliary relay panel) is okay.
Have ignition switch on in all program switch positions unless told otherwise. Turn ignition off before connecting or disconnecting ABS control unit.
To find a fault in system, the testing procedure must be followed completely and in the specified sequence. When cause of fault is found, it should be repaired. The entire test procedure should then be repeated, starting from step one.

Fig 1: ABS Components ID (80/90 Quattro)

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Fig 2: ABS Components ID (90 2WD)

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Fig 3: ABS Components ID (200 Turbo, 5000 & 5000CS Turbo)

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Fig 4: ABS Components (100/200 & 5000CS Quattro)

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