Safety Precautions And Troubleshooting

Troubleshooting

The ABS is a safety system; knowledge of the system is required when performing repairs or other work.
Always check Diagnostic Trouble Code (DTC) memory before performing any work on the ABS system.
Do not drive the vehicle when the harness connector is disconnected from the ABS control module.
Ignition must be switched off when disconnecting or connecting harness connectors.
Do not loosen bolts on the ABS hydraulic unit (this does not apply to the relay cover).
Observe normal safety precautions when working with break fluid HYDRAULIC SYSTEM, BLEEDING .
Malfunctions in the ABS system are indicated by the ABS warning light; certain malfunctions are only recognized when the vehicle exceeds 12 km/h (7.2 mph) (road test).
For information on repairing actual malfunctions ANTILOCK BRAKE SYSTEM .

Test Prerequisites

Same tire sizes (as specified) on all four wheels; tires inflated to specified pressures
Conventional brake system functioning properly, including brake light switch, left and right brake lights
No leaks from hydraulic connections or lines (visual check of ABS hydraulic unit, brake master cylinder)
Wheel bearing and wheel bearing play OK
Ground connection for ABS return flow pump -V39- OK (on ABS hydraulic unit)
ABS return flow pump relay -J105- and ABS solenoid valve relay -J106- - correctly connected
Harness connector on ABS Control Module (w/EDL) -J104- correctly connected (positive engagement)
When using the scan tool :VAG1551 , test box VAG 1598 must not be connected to the ABS Control Module (w/EDL) -J104-.
All fuses OK according to wiring diagram
Battery positive voltage (B+) OK (min. 10.5 V)

Required Technical Information