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 turn the wheel to be measured 1/2 to 1 turn/second. Measure the output voltage with a voltmeter or oscilloscope.
Output voltage:
^ Voltmeter reading: 42 mV or higher
^ Oscilloscope reading: 120 mV or higher
4. If the output voltage is lower than that given above, the cause may be the following, so check or replace the ABS sensor if necessary.
^ Wheel speed sensor pole piece-to-ABS rotor clearance too large
^ Faulty wheel speed sensor
WAVE PATTERN INSPECTION USING AN OSCILLOSCOPE
After checking the connection of the wheel speed sensor harness and the connector, take a reading of the output voltage wave patterns for each wheel speed sensor using an oscilloscope as follows.
Start the engine, shift the selector lever to D range, and then spin the wheels.
NOTE:
^ For rear wheels, turn the wheels manually at a constant speed
^ You can also take a reading of the wave pattern by actually driving the vehicle in this condition.
^ The output voltage will be lower when the wheel speed is lower, and will become higher as the wheel speed becomes higher.
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.