Wheel Speed Sensor: Testing and Inspection

TOOTHED ABS ROTOR CHECK





Check whether the ABS rotor teeth are broken or deformed. Replace the driveshaft assembly for the front side or the ABS rotor for the rear side, respectively, if the teeth are damaged or deformed.

WHEEL SPEED SENSOR OUTPUT VOLTAGE MEASUREMENT
Required 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:
- Minimal voltmeter reading: 42 mV
- Maximum voltmeter reading: 300 mV
- Minimal oscilloscope reading: 120 mV
- Maximum oscilloscope reading: 600 mV
Probable causes of low output voltage
- Wheel speed sensor pole piece-to-ABS rotor clearance too large
- Faulty wheel speed sensor





NOTE: Check the connection of the sensor harness and connector before using the oscilloscope.

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: The output waveform is low when the wheel speed is low. Similarly, it will be higher as the wheel speed increases.

Waveform may also be observed by driving the vehicle.





POINTS IN WAVEFORM MEASUREMENT