Brake Fluid Pressure Sensor/Switch: Description and Operation
BRAKE WARNING LIGHT SWITCHESWhen a pressure differential occurs between the front and rear brake systems, the valves will shuttle toward the side with the low pressure. Movement of the differential valve forces the switch plunger upward over the tapered shoulder of the valve to close the switch contacts and light the dual brake warning lamp, signaling a brake system failure.
The valve assembly consists of two valves in a common bore that are spring loaded toward the centered position. The spring-loaded switch contact plunger rests on top of the valves in the centered position. When a pressure differential occurs between the front and rear brake systems, the valves will shuttle toward the side with the low pressure. The spring-loaded switch plunger is triggered and the ground circuit for the warning light is completed, lighting the lamp.
As pressure falls in one system, the other system's normal pressure forces the piston to the inoperative side, contacting the switch terminal, causing the warning light on the instrument panel to glow.
On front wheel drive models, a fluid level indicator replaces the pressure differential valve used in previous brake systems. It is contained inside the body of the master cylinder plastic reservoir and activates the brake warning light when fluid level is low.
BRAKE DISTRIBUTION VALVE & SWITCH
This switch assembly which is used on some diagonally split brake systems, is connected to the outlet ports of the master cylinder and also to the brake warning light that warns the driver if either the primary or secondary brake system has failed.
When hydraulic pressure is equal in both primary and secondary brake systems, the switch remains centered. If pressure fails in one of the systems, hydraulic pressure moves the piston toward the inoperative side. The shoulder of the piston contacts the switch terminal, providing a ground and lighting the warning lamp.