Brake Fluid Level Sensor/Switch: Description and Operation

The purpose of the brake fluid level switch is to provide the driver with early warning that brake fluid in the master cylinder is below a normal level.

Master Cylinder Reservoir Level Sensor:

The brake fluid level switch used on this vehicle's master cylinder is internal to the master cylinder fluid reservoir. The vehicle wiring harness has a connector which plugs directly into the brake fluid reservoir.
As the fluid drops below the design level the switch closes the Red BRAKE Warning Lamp circuit. This will turn on the red brake warning light. At this time, the master cylinder fluid reservoir should be checked and filled to the full mark with DOT 3 brake fluid. If the brake fluid level has dropped in the master cylinder fluid reservoir, the entire brake hydraulic system should be checked for evidence of a leak.
The brake fluid level switch in the master cylinder brake fluid reservoir is not a repairable item. If the level switch is found to be defective the brake fluid reservoir must be replaced.