The fault could be lack of hydraulic fluid, low brake fluid in the reservoir, a broken hydraulic line or a bad master brake cylinder. The sensor is used to detect pressure differentials in the hydraulic system. If the car alerts a fault in the hydraulic system and the system checks out, the sensor itself may have failed.[2]
Design
The sensor has an input port to measure the hydraulic braking pressure and an electrical connector output for a wire connection for feeding the warning light. Some brake failures do not trip the sensor into a fault mode.
A brake fluid pressure sensor is used in anti-lock braking system (ABS). ABS fault lights come on with unexpected wheel lock from the ABS system, but could also include low fluid in the reservoir.[3][4][5][6]
