Wheel Speed Sensor: Description and Operation

Wheel Speed Signal Conditioner Module






The wheel speed signal conditioner module for the L81 application is only equipped on vehicles without antilock brakes. The wheel speed signal conditioner module is located under the driver side I/P, which is orange in color and similar dimensionally to a relay. The module harness is tied to the I/P harness.

Important: The speedometer is ran off the output speed sensor signal, which is the direct input to the transmission control module (TCM). The TCM sends vehicle speed information over the controller area network (CAN) link to the body control module (BCM). The BCM in turn will send a message over the Class II link to the I/P cluster which will position the speedometer.

Vehicle speed on non-ABS vehicles is received from the right front wheel speed sensor. The wheel speed signal conditioner module is used to convert the A/C voltage of the sensor to a square wave. This is accomplished by pulse width modulating the vehicle speed output circuit to ground, which is pulled up to 12 volts through resistance in the ECM. The ECM interprets the square wave input as vehicle speed.