Mitsubishi Electric Lancer Evolution-VII Workshop Manual page 774

When turning by hand
When idling (5 - 6 km/h), 1st gear
10.0 ms/DIV 1 V/DIV
Points In Waveform Measurement
Symptom
Too small or zero waveform
amplitude
Waveform amplitude fluctuates
excessively (this is no problem if excessively (this is no problem if
the minimum amplitude is 100 mV
or more)
ABS <4WD> -
On-vehicle Service
4. Rotate the wheel to be measured at approximately 1/2 - 1
rotation per second, and check the output voltage using a
circuit tester or an oscilloscope.
Wheel speed
sensor
Terminal No.
Output voltage
When measuring with a circuit tester:
When measuring with an oscilloscope:
5. The followings are suspected if the output voltage is lower
than the value described above. Check the wheel speed
sensor, and replace if necessary.
Too large clearance between the pole piece of the
D
wheel speed sensor and ABS rotor
Faulty wheel speed sensor
D
Inspecting Waveforms With An Oscilloscope
Use the following method to observe the output voltage
waveform from each wheel speed sensor with an oscilloscope.
Start the engine, and rotate the front wheels by engaging
D
1st gear. Turn the rear wheels manually so that they
rotate at a constant speed.
NOTE
1. The waveform measurements can also be taken while
the vehicle is actually moving.
2. The output voltage will be small when the wheel speed
is low, and similarly it will be large when the wheel speed
is high.
Probable causes
Faulty wheel speed sensor
Axle hub eccentric or with large runout
Faulty ABS-ECU earth
Front Front
left right
22 29
31 30
42 mV or more
120 mV p-p or more
35B-27
Rear Rear
left right
6 8
7 9
Remedy
Replace sensor
Replace hub
Repair