Wheel Speed Sensor: Testing and Inspection
WHEEL SPEED SENSOR OUTPUT VOLTAGE MEASUREMENTRequired Special Tool: MB991219: Inspection Harness
1. Lift up the vehicle and release the parking brake.
2. Disconnect the ABS-ECU connector, and then use special tool MB991219 to measure the output voltage at the harness side connector.
3. Manually turning the wheel to be measured by 1/2 to 1 turn/second, measure the output voltage with a voltmeter or oscilloscope.
Output voltage:
When measured with voltmeter: 42 mV or more
When measured with oscilloscope (maximum voltage): 120 mV or more
Probable causes of low output voltage
- Wheel speed sensor pole piece-to-ABS rotor clearance too large
- Faulty wheel speed sensor
4. To observe the waveform with an oscilloscope:
Front Wheels:
Shift into low gear and drive the wheels.
Rear Wheels:
Turn the wheels manually at a constant speed.
NOTE:
- Waveform may also be observed by driving the vehicle.
- The output voltage is low when the wheel speed is low. Similarly, it will be higher as the wheel speed increases.
- Check the connection of the sensor harness and connector before using the oscilloscope.
Points In Waveform Measurement
NOTE: The wheel speed sensor cable moves in relation to motion of the front or rear suspension. Therefore, it is likely that it has an open circuit only when driving on rough roads but it functions normally when driving on smooth roads. It is recommended to observe sensor output voltage waveform also under special conditions, such as driving on a rough road.