Volvo Coupes/Sedans/Wagons 1970-1989 Repair Guide

Warning Valves


See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Location of brake system valves on the chassis-common 200 series shown


The brake system warning valve is located near the master cylinder in the engine compartment on 1973-77 models. On 1978 and later models it is located under a bolt on the front axle member. The 700 Series vehicles without ABS have the unit mounted on the left front shock tower. The valve is centered by hydraulic pressure from the primary circuit on one side and the secondary circuit on the other.

When a hydraulic imbalance occurs, such as a leak in one of the calipers, the valve will move off-center toward the system with the lower pressure. When the valve moves off-center, it closes a circuit to a warning light on the dashboard, warning the driver of the imbalance. Sometimes, the valve will actuate the warning light when one of the systems is bled during normal maintenance. When this happens, the valve has to be reset.

Cars with ABS do not use this system. The pressure sensing circuit is built into the hydraulic unit. In case of system leakage, a sensor within the cap of the brake fluid reservoir will close a switch and illuminate the dash warning light.

If the valve must be replaced:

  1. Place a rag beneath the valve to catch the brake fluid, loosen the pipe connections, label and disconnect the six brake lines. Disconnect the electrical plug contact, and lift out the valve.
  3. Connect the new warning valve in the and connect the plug contact.
  5. Bleed the entire brake system.


1800, 100 and 200 Series
  1. Disconnect the plug contact and screw out the warning switch so that the pistons inside the valve may return to their normal position.
  3. Repair and bleed the faulty hydraulic circuit.
  5. Screw in the warning switch and tighten it to a torque of 10-14 ft. lbs. (13-19 Nm). Connect the plug contact.
  7. When the system has been bled, depress the brake pedal firmly (simulating a hard stop) for about a minute. Check that there has been no leakage at the warning switch threads. If any leakage-no matter how slight-is found, replace the valve assembly.

The non-ABS 700 Series vehicles do not require this procedure. The valve will self-center once equal pressures have been restored within the system.