Wheel Speed Sensor: Description and Operation

OPERATION
One wheel speed sensor (WSS) is located at each wheel and sends a small AC signal to the control module (CAB). This voltage is generated by magnetic induction when a toothed sensor ring (tone wheel) passes by a stationary magnetic sensor (wheel speed sensor). The CAB converts the AC signals into 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 front wheel speed sensor air gap is NOT adjustable. The correct front wheel speed sensor air gap is from 0.40mm to 1.3mm. Preferred rear sensor air gap for drum brake systems is 1.1 mm. Acceptable air gap range is 0.92mm to 1 0.275mm. For rear disc brake systems, the preferred rear sensor air gap is 1.2mm. Acceptable air gap range is 0.95mm to 1.45mm. All wheel speed sensors have a resistance between 900 and 1300 ohms.

Correct antilock system operation is dependent on tone 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).

CIRCUIT OPERATION
The all wheel antilock system uses four wheel speed sensors; one for each wheel. Each sensor converts wheel speed into an electrical signal that it transmits to the Anti-Lock Brake System (ABS) control module. A pair of twisted wires connect to each sensor to provide signals to the ABS control module.

Circuits B6 and B7 provide signals to ABS control module from the right front wheel speed sensor. Circuit B6, which provides the LOW signal, connects to cavity 29 of the ABS control module. Circuit B7 connects to cavity 47 of the module and provides the HIGH signal.

Circuits B8 and B9 provide signals to ABS control module from the left front wheel speed sensor. Circuit B8, which provides the LOW signal, connects to cavity 30 of the ABS control module. Circuit B9 connects to cavity 48 of the module and provides the HIGH signal.

Circuits B1 and B2 provide signals to ABS control module from the right rear wheel speed sensor. Circuit B1 which provides the LOW signal, connects to cavity 27 of the ABS control module. Circuit B2 connects to cavity 45 of the module and provides the HIGH signal.

Circuits B4 and B3 provide signals to ABS control module from the left rear wheel speed sensor. Circuit B3, which provides the LOW signal, connects to cavity 28 of the ABS control module. Circuit B4 connects to cavity 46 of the module and provides the HIGH signal.