Mitsubishi Evolution X. Manual - part 762

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-55

DTC C1027: Abnormality in RL wheel speed sensor signal

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.

.

AC708948

Connector: A-05

A-05 (B)

AB

AC708950

Connector: C-45

AD

AC708955

Connector: D-18

D-18 (B)

AE

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-56

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.

• Irregular change in the wheel speed sensor signal

• Wheel speed sensor signal continuously indicates higher 

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

• Adhesion of foreign materials on the magnetic encoder for 

wheel speed detection

• Wheel bearing malfunction

• Malfunction of wheel speed sensor

• Damaged wiring harness and connectors

• External noise interference

• Improper installation of the wheel speed sensor

• Deformation of the magnetic encoder for wheel speed 

detection

• ASC-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 the diagnostic trouble code No.C1020 is not set, the 

following conditions may be present:

• Wheel(s) spinning

• Unstable vehicle attitude (spin)

• External noise interference

• Vehicle ran with the parking brake applied.

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-57

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 C1027 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 16.

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 16.

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-58

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. Voltage measurement at A-05 ASC-ECU connector
(1) Disconnect the ASC-ECU connector, connect the ASC 

check harness (Special tool: MB991997) to the wiring 
harness-side connector, and then measure at the special 
tool connector side.
NOTE: Do not connect the special tool to ASC-ECU.

(2) Turn the ignition switch to the ON position.
(3) Measure the voltage between the wheel speed sensor 

circuit power supply terminal (signal terminal) No. 36 and 
the body ground as well as between the ground terminal 
No. 37 and the body ground.

OK: 1 volt or less

Q: Is the check result normal?

YES  : Go to Step 9.
NO (Not normal at the terminal No. 36 or 37) : Go to Step 

10.

AC608248AB

Magnetic
encoder

Rear Wheel
bearing

Rear wheel
hub
assembly

AC400817CH

ASC-ECU

MB991997

Check harness

A-05 ASC-ECU
harness connector