TEVES Abs System Description: Sensors

Wheel Speed Sensors and Tone Wheels:  One wheel speed sensor (WSS) is located at each wheel and sends a small digital signal to the control module (CAB). The CAB sends 12 volts down to the sensor. The sensor has an internal magneto resistance bridge that alters the voltage and amperage of the signal circuit. This voltage and amperage is changed by magnetic induction when a toothed sensor ring (tone wheel) passes by a stationary magnetic sensor (wheel speed sensor). The CAB measures the voltage and amperage of the digital signals for each wheel.

The front wheel sensor is attached to a boss in the steering knuckle. The tone wheel is an integral part of the front axle shaft. The rear speed sensor is mounted in the caliper adapter plate (rear disc only) and the rear tone wheel is an integral part of the rear rotor hub. The wheel speed sensor air gap is NOT adjustable. Because of internal circuitry, a resistance check of wheel speed sensors will not determine correct or incorrect function. 

Correct anti-lock system operation is dependent on wheel speed signals from the wheel speed sensors. The vehicle's wheels and tires should all be the same size and type to generate accurate signals. In addition, the tires should be inflated to the recommended pressures for optimum system operation. Variations in wheel and tire size or significant variations in inflation pressure can produce inaccurate wheel speed signals; however, the system will continue to function when using the mini-spare. When driven over rough road surfaces, the rear wheel speed sensor signals may be erratic and cause a false trouble code (drum brakes only).

Brake Warning Indicator Switch:  The brake warning indicator switch is a fluid level sending switch. The CAB sends out a 12 volt signal to the switch. The switch has a 1,000 ohm resistor inside of it. This resistor is used for diagnostic purposes. Normal voltage is about 2.3 volts. If the switch is disconnected the resistor will be pulled out of the circuit and the CAB will sense voltage at about 5 volts. If the fluid level becomes too low or the circuit is shorted to ground, the voltage will be about 0 volts. Any fault condition will illuminate the red brake warning indicator and the specific fault can be read on the DRBIII(R).