Normal Operation
WARNING: This page is about a different car, the 2006 Mercury Milan, 2006 Lincoln Zephyr, and 2006 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
Active wheel speed sensors generate a square wave signal that is sent to the anti-lock brake system (ABS) module. The wheel speed sensor circuitry connects to the ABS module C135 through 2 wires and a connector at each wheel speed sensor. When the ignition switch is turned to the RUN position, the ABS module carries out a self-test by sending a reference voltage through the wheel speed sensors and their circuitry to determine if they are functional.
Battery voltage is supplied to the active wheel speed sensors from the ABS module. The wheel speed sensor ground is supplied by the ABS module.