Volvo Coupes/Sedans/Wagons 1970-1989 Repair Guide

Anti-lock Brake System (ABS)


The ABS system comprises many components including sensors, pulse-wheels, the hydraulic modulator and the Electronic Control Unit (ECU). The ECU is the "brain" of the system while the modulator performs the actual work of controlling the fluid flow to each wheel. Testing of the system requires specific dealer-only equipment. The hydraulic unit, located either in the trunk or under the hood, is connected to a maze of brake lines. Don't attempt to loosen, bleed or repair anything at this unit.

Under very hard braking, you may hear unusual sounds from the hydraulic modulator; this is quite normal and is simply a result of the unit doing its job.

The ABS warning light on the dash should not be confused with the brake warning light. If the ABS light comes on, it indicates a fault in the Anti-lock system, not the main braking system. The car can be safely driven, but will not have the benefit of the ABS system. If the brake warning light comes on, the braking system may be impaired due to fluid loss in the system. In this case braking may be reduced; diagnosis and repair is required immediately and caution should be used when driving.


Disc brakes are inherently self adjusting. The only adjustment needed will be for the parking brakes, which are small brake shoes located in the hub drum of the rear disc brake rotors. See the end of this section for procedures.