Functional Description - Wheel Speed Sensors

The Wheel Speed Sensors can be a magnetic pickup type or Hall Effect type sensor depending on the system being used. Each system uses a different type of target. The ABS Module provides a signal voltage to the sensor and a ground path. The signal voltage can be 5v or 12v depending on the system.

• The system with magnetic pickup type sensors typically use a metal tone wheel that can be mounted on the hub/bearing assembly or front axle shaft. The tone wheel will have high and low spots equally spaced around the tone wheel. As the wheel is turning the high/low spots on the tone wheel pass the magnet in the sensor causing a square wave 5v or 12v signal.
• The system with Hall Effect sensors use a magnetic pole encoder that is typically incorporated in the wheel bearing assembly. With this system the air gap between the WSS and encoders is not adjustable. As the wheel is turning the magnets in the encoder pass the Hall Effect sensor causing a square wave 5v or 12v signal.

The PCM uses the Wheel Speed Sensor signals and Steering Angle Sensor signal for Engine Stop/Start enabling and oil aeration detection. The PCM rationalizes the Wheel Speed Sensor signals against each other and uses the Wheel Speed Sensor signals to rationalize the Steering Angle Sensor signal.

• If the wheel speed signals are showing vehicle speed present, the PCM will disable ESS mode.
• If the vehicle is in a hard turning event, as determined by the wheel speed signals the oil can be dispersed to one side of the oil pan away from the pickup tube on some vehicles. This can cause oil aeration and affect the valve timing performance fault detection. During a hard turning event the valve timing performance diagnostics will be suspended until the event ends.