1990 Audi 90 Quattro Anti-lock Brake System (ABS) Diagnosis Cost

This system was designed with occupant safety in mind. The anti-lock braking (ABS) system is used to maintain wheel motion and traction while braking, accelerating or cornering on a slippery surface. This system uses the same components as the traction control system (TCS), and the functionalities of both are integrated through the ABS control module.

The ABS system is designed to keep the brakes from stopping one or more wheels while the vehicle is in motion by quickly engaging and disengaging the brakes in rapid succession until the vehicle is out of harm's way. The ABS control module is the brain of this system, and is physically attached to the brake lines, via the distribution block, to control the amount of pressure that is being applied when the driver depresses the brake pedal. Because traction control is integrated into the ABS system, the ABS module may pulse the brakes or reduce engine power during cornering to prevent wheel spin, even if the brakes are not applied.

A failure in the ABS or TCS will leave the brakes functioning normally, but without the added security of traction control and anti-lock brakes. When the ABS control module detects a fault, the ABS light, traction control light, and any manufacturer specific stability control lights will illuminate on the instrument cluster, alerting you to have the systems inspected for faults.

The vehicle can be driven with these warning lights on, since failure of the ABS or TCS does not disable the vehicle, but safety is a concern as drivers become accustomed to the road manners of their vehicles. If hard braking that is normally controlled by the ABS control module is necessary, a collision may occur. We do recommend towing the vehicle to a repair facility if the brakes feel unusual under light or normal driving conditions. Get this fixed by a RepairPal Certified Shop

ABS system components can fail at any mileage, and under any conditions. However the wheel speed sensors, which monitor the speed of wheel rotation, are prone to failure as they are housed near the road surface, and subject to dust, debris, precipitation, salt, and road hazards.

Anti-lock braking systems are complex, and are typically diagnosed through professional computer scanning equipment, or manufacturer specific software. The technician will communicate with the ABS control module via computer, and view real-time data to determine what fault has been detected, and how the system is behaving. Once the technician identifies a suspected failure in the system, physical inspection and probing will take place to ensure an accurate diagnosis.

Although it is possible to change minor components of the ABS system, such as a wheel speed sensor, it is not recommended to do so unless a specific diagnosis can be reached. There are many possible reasons for the ABS module to signal a fault, and personal scanning tools will only specify a condition, not a faulty part. For cost savings, only replace parts after a set of diagnostic tests have been conducted.

Certain parts of the ABS system can be DIY friendly, but diagnosing ABS and TCS trouble codes requires advanced knowledge, professional computerized diagnostic equipment, and manufacturer software. This entire system is best left to a professional technician, and is not advised for the DIY.