Traction Control/Active Stability Control System (TCL/ASC)

WHEEL SPEED SENSOR OUTPUT VOLTAGE MEASUREMENT

Required Special Tool:

MB991997: ASC Check Harness

1. Release the parking brake and lift up the vehicle.





2. Disconnect the TCL/ASC-ECU connector A-38, and then use special tool MB991997 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.
NOTE:
Check the connection of the sensor harness and connector before using the 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-Wheel speed rotor clearance too large
- Faulty Wheel speed sensor
4. To observe the waveform with an oscilloscope:

- Front Wheels: Shift into 1st gear[ M/T] or "D" range[ A/T] 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





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.