Brake System Sensors

Electronics have improved the function of every system on modern vehicles and your brakes are no different. Anti-lock brake systems that prevent wheel lockup for safe, controlled stops are commonplace today, as are warning systems for brake fluid pressure, fluid level, pad wear, and parking brakes. All of these systems use sensors and switches to input data to control modules and open and close electric circuits.

The most important sensors and switches alert you to problems in your brake system like a loss of pressure and low fluid level. The pressure differential switch illuminates a brake warning light when there is a leak and a loss of pressure in a hydraulic circuit. A leak will cause a low brake pedal and diminished braking capability, and the brakes should be inspected immediately. Low fluid level in the master cylinder can also be caused by a leak.

When the parking brakes are applied, a switch illuminates a warning light to remind you to release them before driving. Driving with the parking brakes on will cause excessive wear, and possibly costly damaged if the vehicle is driven a distance. The stop lamp switch is mounted on the brake pedal and activates the brake lights when you push on the pedal. On some vehicles the same switch also turns off the cruise control and torque converter clutch when the pedal is depressed. Some newer vehicles use a brake pedal position sensor instead of a switch that provides input to the engine and body control modules.

The ABS warning light will come on if there is a fault in the system. The ABS system will turn off, but regular braking usually will not be affected as long as the brake warning light isn’t on. The system should be diagnosed as soon as possible to restore ABS function. The ABS wheel speed sensor sends a voltage signal to the ABS control module indicating wheel speed. During braking, if one wheel slows down much faster than the others, the control module will reduce hydraulic pressure to that wheel to prevent lockup. The sensor is mounted next to a toothed ring on the wheel hub, axle shaft, or differential ring gear.

Many vehicles with disc brakes are equipped with pad wear sensors. On most systems the sensors are attached to the pads, and when the pads wear to a predetermined thickness, the sensors contact the brake rotors and illuminate a light on the dash, alerting the driver that pad replacement is needed. The position of the sensor is calibrated to leave enough pad material to allow time for the repair to be scheduled. Since pad wear sensors are “sacrificial components”, they must be replaced along with the pads. You’ll find these sensors and any other brake sensors and switches you need on our digital shelves.