Pressure Differential Valve and Warning Lamp Switch

Differential Valve And Brake Warning Switch:

The pressure differential valve and warning lamp switch is part of the combination valve to alert the driver in the event pressure drops in one of the brake hydraulic systems. The function of the pressure differential switch and warning lamp switch are described in detail below.

The brake hydraulic system on this vehicle is vertically split. This means the brake hydraulic system is equally split between the front and rear brakes, with both front brakes on one hydraulic system and both rear brakes on the other. This differs from the brake hydraulic system on a front wheel drive car which is diagonally split. On a brake hydraulic system which is diagonally split, the left front and right rear brake is on one hydraulic system and the right front brake and left rear brake on the other.

The primary and secondary hydraulic circuit from the master cylinder is separated into a vertically split hydraulic circuit by the internal passages of the combination valve.

The pressure differential valve, which is internal to the combination valve, is used to monitor the pressure in the brake hydraulic system. The pressure differential valve functions by simultaneously sensing that the hydraulic pressure in the primary and secondary hydraulic circuit from the master cylinder and the front and rear brake hydraulic circuits is equal.

If the pressure in the brake hydraulic circuits is equal when the brake pedal is depressed, the differential valve will stay centered in the combination valve and the red brake warning lamp will not be turned on. If pressure in one of the brake hydraulic circuits drops when the brake pedal is depressed, the drop in pressure will cause the pressure differential valve to move off center in the combination valve. As the pressure differential valve moves off center it pushes the plunger up into the brake warning lamp switch. When the plunger is pushed into the brake warning lamp switch, a ground for the red brake warning light circuit is completed. Creating the ground for the red brake warning lamp circuit will turn on the red brake warning lamp located in the instrument cluster.

If the Red Brake Warning Lamp is turned on, the brake system requires immediate service. However, since the brake hydraulic systems are split front to rear, the vehicle will retain half of its stopping capability in the event of a failure in either half of the system.

Note: The brake warning light switch is the latching type. It will automatically center itself only after the repair is made and the brake pedal is depressed.

The instrument panel bulb in the Red Brake Warning Light is automatically turned on each time the ignition switch is turned to the start position as a bulb check. The red brake warning lamp is also turned on when the parking brake is set.