Mitsubishi Evolution X. Manual - part 767

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-75

STEP 8. Check whether the DTC is reset.
(1) Erase the diagnostic trouble code.
(2) Drive the vehicle at 12mph (20 km/h) or more.

NOTE: The ABS warning light does not turn OFF in some 
cases unless the vehicle runs at 12mph (20 km/h) or higher.

Q: Is DTC C101F set?

YES : Replace the hydraulic unit (incorporates in 

ASC-ECU).(Refer to 

P.35C-272

.) Then go to Step 9.

NO :  Intermittent malfunction. (Refer to GROUP 00 

− How 

to Cope with Intermittent Malfunction 

P.00-15

.)

STEP 9. Check whether the DTC is reset.
(1) Erase the diagnostic trouble code.
(2) Drive the vehicle at 12mph (20 km/h) or more.

NOTE: The ABS warning light does not turn OFF in some 
cases unless the vehicle runs at 12mph (20 km/h) or higher.

Q: Is DTC C101F set?

YES : Return to Step 1.
NO :  This diagnosis is complete.

DTC C102A: Mutual monitoring of RL wheel speed sensor

CAUTION

• If there is any problem in the CAN bus lines, an incor-

rect diagnostic trouble code may be set. Prior to this 
diagnosis, diagnose the CAN bus lines.

• Whenever the ECU is replaced, ensure that the CAN 

bus lines are normal.

• When the hydraulic unit (integrated with ASC-ECU) is 

replaced, always perform the calibration of steering 
wheel sensor, G and yaw rate sensor, brake fluid pres-
sure sensor, cut valve, and inlet valve.(Refer to 

P.35C-266

, 

P.35C-267

, 

P.35C-268

, and 

P.35C-269

.)

.

CIRCUIT OPERATION

• Each wheel speed detecting section is a kind of a pulse 

generator. It consists of the encoder (plate on which the 
north and south pole of magnet are arranged alternately) for 
detecting the wheel speed, which rotates at the same speed 
of the wheels, and the wheel speed sensor. This detecting 
section outputs the frequency pulse signals in proportion to 
the wheel speed.

• The pulse signals generated by the wheel speed detecting 

section are sent to ASC-ECU. ASC-ECU uses the fre-
quency of the pulse signals to determine the wheel speed.

.

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-76

DTC SET CONDITIONS

ASC-ECU monitors the signals from each wheel speed sensor 
while the vehicle is being driven. If any abnormality below is 
detected in the sensor signals, ASC-ECU sets the relevant 
diagnostic trouble code.

• Missing wheel speed sensor signal

• Wheel speed sensor signal continuously indicates lower 

value than the values of other wheel speed sensors.

.

PROBABLE CAUSES

Current trouble

• Excessive gap between the wheel speed sensor and the 

magnetic encoder for wheel speed detection

• Adhesion of foreign materials on the wheel speed sensor

• Wheel bearing malfunction

• Deformation of the magnetic encoder for wheel speed 

detection

• Adhesion of foreign materials on the magnetic encoder for 

wheel speed detection

• Malfunction of wheel speed sensor

• Improper installation of the wheel speed sensor

• ABS-ECU malfunction

• Disturbance of magnetization pattern for magnetic encoder 

for wheel speed detection

• The number of poles on the magnetic encoder for wheel 

speed detection (the number of N-pole and S-pole) is 
changed.

Past trouble

• When DTC No. C1020 is also set, perform the diagnosis 

with a particular emphasis on the wiring harness and con-
nector failures between ASC-ECU and the wheel speed 
sensor. For diagnosis procedures, refer to How to Treat 
Past Trouble (GROUP 00 

− How to Use Troubleshoot-

ing/Inspection Service Points 

P.00-16

).

• When DTC No. C1020 is not set simultaneously, the follow-

ings can be suspected.

• Wheel(s) spinning

• Unstable vehicle attitude (spin)

• External noise interference

• Vehicle ran with the parking brake applied.

• Only two wheels are rotated on a drum tester.

DIAGNOSIS

Required Special Tools:

• MB991958 Scan Tool (M.U.T.-III Sub Assembly)

• MB991824: Vehicle Communication Interface (V.C.I.)

• MB991827 M.U.T.-III USB Cable

• MB991910 M.U.T.-III Main Harness A

• MB991997: ASC check harness

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-77

STEP 1. Using scan tool MB991958, diagnose the CAN bus 
lines.
Using scan tool MB991958, diagnose the CAN bus lines.
Q: Is the check result normal?

YES : Go to Step 3.
NO :  Repair the CAN bus lines. (Refer to GROUP 54C 

− 

Troubleshooting 

P.54C-14

.) After repairing the CAN 

bus line, go to Step 2.

STEP 2. DTC recheck after repairing the CAN bus line
Q: Is DTC C102A set?

YES : Go to Step 3.
NO :  This diagnosis is complete.

STEP 3. Scan tool diagnostic trouble code
Check if DTC No. C1020 is also set.
Q: Is DTC C1020 also set?

YES : Carry out the diagnosis for code No. C1020. ( Refer to 

P.35C-33

.)

NO :  Go to Step 4.

STEP 4. Check of wheel speed sensor installation status
Check the installation status of wheel speed sensor <RL> (dis-
connection of wheel speed sensor, looseness of mounting bolt, 
etc.).
Q: Is the check result normal?

YES : Go to Step 5.
NO :  Reinstall the wheel speed sensor <RL> correctly. 

(Refer to 

P.35C-274

.) Then go to Step 9.

STEP 5. Check of wheel speed sensor as a single unit
Refer to 

P.35C-277

.

Q: Is the check result normal?

YES : Go to Step 6.
NO :  Replace the wheel speed sensor <RL>. (Refer to 

P.35C-274

.) Then go to Step 9.

STEP 6. Wheel bearing looseness check
NOTE: Wheel bearing looseness may increase the gap 
between the wheel speed sensor and the wheel speed detec-
tion magnet encoder. Check the wheel bearing <RL> for loose-
ness. (Refer to GROUP 27 

−

 On-vehicle Service 

P.27-33

.)

Q: Is the check result normal?

YES : Go to Step 7.
NO :  Replace the rear wheel hub assembly. (Refer to 

GROUP 27 

− Rear Axle Hub Assembly 

P.27-36

.)

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-78

STEP 7. Check of wheel speed detection encoder
Check the encoder for adhesion of foreign materials or defor-
mation.
Q: Is the check result normal?

YES  : Go to Step 8.
NO (Adhesion of foreign materials) : Clean the encoder 

so as not to disturb the magnetization pattern on the 
encoder while taking care of the magnet, magnetic 
substance, and magnetic attraction.

NO (Deformation) : Replace the rear wheel hub assembly. 

(Refer to GROUP 27 

− Rear Axle Hub Assembly 

P.27-36

.)

STEP 8. Check whether the DTC is reset.
(1) Erase the diagnostic trouble code.
(2) Drive the vehicle at 12mph (20 km/h) or more.

NOTE: The ABS warning light does not turn OFF in some 
cases unless the vehicle runs at 12mph (20 km/h) or higher.

Q: Is DTC C102A set?

YES : Replace the hydraulic unit (incorporates in 

ASC-ECU).(Refer to 

P.35C-272

.) Then go to Step 9.

NO :  Intermittent malfunction. (Refer to GROUP 00 

− How 

to Cope with Intermittent Malfunction 

P.00-15

.)

STEP 9. Check whether the DTC is reset.
(1) Erase the diagnostic trouble code.
(2) Drive the vehicle at 12mph (20 km/h) or more.

NOTE: The ABS warning light does not turn OFF in some 
cases unless the vehicle runs at 12mph (20 km/h) or higher.

Q: Is DTC C102A set?

YES : Return to Step 1.
NO :  This diagnosis is complete.

AC608248AB

Magnetic
encoder

Rear Wheel
bearing

Rear wheel
hub
assembly