WHEEL SPEED SENSOR OUTPUT VOLTAGE MEASUREMENT


1.Lift up the vehicle and release the parking brake.

2.Move the lock lever of the ABS-ECU connector as shown in the illustration, and then disconnect the ABS-ECU connector A-01.

3.Connect special tool ABS check harness (MB991952) to the wiring harness-side connector.
note Do not connect special tool ABS check harness (MB991952) to the ABS-ECU.
4.Manually turn the wheel to be measured 1/2 to 1 turn/second. Measure the output voltage with a voltmeter or oscilloscope.

TERMINAL NO.
Front left
 Front right
 Rear left
 Rear right
4
 26
 23
 1
5
 27
 24
 2
Output voltage:
    42 mV or higher when measured using a multimeter
    120 mVP-P or higher when measured using a oscilloscope
5.If the output voltage is lower than that given above, the cause may be the following, so check or replace the wheel speed sensor if necessary.

  • Wheel speed sensor pole piece-to-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, the transmission selector lever to D range, and then spin the wheel.

note
  • 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
Symptom
 Probable causes
 Remedy
Too small or zero waveform amplitude
 Faulty wheel speed sensor
 Replace sensor
Waveform amplitude fluctuates excessively (This is no problem if the minimum amplitude is 100 mV or more)
 Axle hub eccentric or with large runout
 Replace hub
Faulty ABS-ECU earth
 Repair harness
Noisy or disturbed waveform
 Open circuit in wheel speed sensor
 Replace sensor
Open circuit in harness
 Repair harness
Incorrectly mounted wheel speed sensor
 Mount correctly
Rotor with missing or damaged teeth
 Replace ABS rotor
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.