Wheel Speed Sensors

WHEEL SPEED SENSORS
The EBC 325 ABS system uses one wheel speed sensor on each front wheel, and one speed sensor mounted in the rear axle for the rear wheels.

The EBC 2 uses only one speed sensor mounted in the rear axle for the rear wheels.

The sensor measures the wheel speed by monitoring a rotating tone wheel. The signal generated by the sensor and tone wheel is transmitted to the CAB.

Each sensor has:
^ a metal tone wheel with teeth on its outside diameter
^ a magnetic coil pick-up (speed sensor) that is mounted to a fixed component
^ an air gap between the tone wheel and the speed sensor assembly

As the teeth of the tone wheel move through the magnetic field of the sensor, an AC voltage is generated. This signal frequency increases or decreases proportionally to the speed) of the wheel. The CAB monitors this signal to check for a sudden change in single or multiple wheel decelerations. If the deceleration of one or more wheels is not within a predetermined amount, the antilock module takes control.

Diagnostically, the coil of wheel speed sensors have different amounts of resistance based upon the sensor type. When measured across the connector's two terminals, the resistance should be:

Front sensors - 2500-2955 ohms
Rear sensor - 1600-2300 ohms.


NOTE: FOR ALL RESISTANCE RANGES ADD 30% TO THE VALUE FOR EXTREME HEAT, SUBTRACT 30% FOR EXTREME COLD.)

The rear wheel speed sensor used on all vehicles have the same resistance value, but; there are two different sensors. Therefore, it is important to replace the rear wheel speed sensor with the proper part.

On an EBC 325 system each front wheel speed is monitored through the speed sensor mounted at the wheel end of the hub. On a EBC 325 and EBC 2 system the rear wheel speed is monitored through the speed sensor mounted in the rear axle assembly.

The CAB will disable antilock controls illuminate the ABS warning light circuit via CCD, and store trouble codes if it detects any of the following on the wheel speed sensor circuits:
^ incorrect circuit resistance when checked with no vehicle movement
^ incorrect sensor output during, vehicle movement
^ erratic sensor output during vehicle movement