ABS - An Introduction
The Bosch manufactured Anti-Lock Braking System (ABS) fitted as standard to the S2 is the same as that fitted to countless other 80/90 quattros. In fact, there are two variants of the ABS system that appeared on the S2.
The system fitted to early cars (MY91 - MY93) is easily spotted by the ABS switch on the dashboard that can be used to turn the system on and off. These early ABS controllers do not have any on-board diagnostic (OBD) capability.
Later cars from (MY94 onwards) have a more sophisticated ABS controller that does support OBD for fault reporting and system diagnosis. On the down side, the ABS cancel switch was deleted from the later controllers to prevent the driver from disabling the system. Other components deleted from the later system were the accelerometer and combination relay.
The ABS is basically a maintenance
free system, but these pages will help to pin-point any potential problems.
A good amount of system testing is relatively easy to perform on the OBD equipped
cars using the VAG1552 tester or a VAG-COM emulator. In order to properly
test the non-OBD equipped cars, special equipment (in the form of a VAG1710
tester - also known as '2LED Tester') is required. The VAG1710 is also required
to diagnose some faults which can fail to register in the memory of OBD equipped
Should you need to get any electric welding work done on the car, be absolutely sure to disconnect the ABS control unit and the battery before work commences. The same applies to the engine ECU of course.
A less well known issue with ABS systems is that they can be damaged by extremes of heat exposure - such as in the drying oven of a bodyshop paint booth. The ABS control unit cannot withstand temperatures of 85 degrees C (185F) for more than two hours and it should never be exposed to temperatures in excess of 95 degrees C (203F).
If disconnecting the ABS control unit, the battery should be disconnected first.
Last Updated 7th October 2002