Mitsubishi Evolution X. Manual - part 754

DIAGNOSIS

TSB Revision

ACTIVE SKID CONTROL SYSTEM (ASC)

35C-23

DIAGNOSTIC TROUBLE CODE PROCEDURES

DTC C100A: Abnormality in FL wheel speed sensor circuit

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.

.

DTC SET CONDITIONS

ASC-ECU monitors the electric current in each wheel speed 
sensor circuit. If an open or short circuit in the wheel speed 
sensor circuit is detected, ASC-ECU sets a corresponding 
diagnostic trouble code.

.

AC708948

Connector: A-05

A-05 (B)

AB

AC708949

Connector: A-11

A-11 (B)

AB

DIAGNOSIS

TSB Revision

ACTIVE SKID CONTROL SYSTEM (ASC)

35C-24

PROBABLE CAUSES

Current trouble

• Damaged wiring harness and connectors

• Noise interference

• Malfunction of wheel speed sensor

• ABS-ECU malfunction

Past trouble

• Carry out the diagnosis with a particular emphasis on the 

wiring harness and connector failures between ASC-ECU 
and the wheel speed sensor. For diagnosis procedures, 
refer to How to Treat Past Trouble (GROUP 00 

− How to 

Use Troubleshooting/Inspection Service Points 

P.00-16

).

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

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 C100A set?

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

STEP 3. Scan tool service data
Check the following service data. (Refer to 

P.35C-255

.)

• Item No.01: FL wheel speed sensor

Q: Is the check result normal?

YES : Go to Step 12.
NO :  Go to Step 4.

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-25

STEP 4. 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 

power supply terminal (signal terminal) No. 45 and the body 
ground as well as between the ground terminal No. 46 and 
the body ground.

OK: 1 volt or less

Q: Is the check result normal?

YES  : Go to Step 5.
NO (Not normal at the terminal No. 45 or 46) : Go to Step 

6.

STEP 5. Resistance 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) Measure the resistance between the wheel speed sensor 

circuit power supply terminal (signal terminal) No. 45 and 
the body ground as well as between the ground terminal 
No. 46 and the body ground.

OK: No continuity

Q: Is the check result normal?

YES  : Go to Step 8.
NO (Not normal at the terminal No. 45 or 46) : Go to Step 

6.

AC400817CB

ASC-ECU

MB991997

Check harness

A-05 ASC-ECU
harness connector

AC400817CC

ASC-ECU

MB991997

Check harness

A-05 ASC-ECU
harness connector

DIAGNOSIS

TSB Revision

ACTIVE SKID CONTROL SYSTEM (ASC)

35C-26

STEP 6. Connector check: A-05 ASC-ECU connector, A-11 
wheel speed sensor <FL> connector
Q: Is the check result normal?

YES : Go to Step 7.
NO :  Repair the defective connector. Then go to Step 13.

STEP 7. Wiring harness check between A-05 ASC-ECU 
connector terminal No. 45 and A-11 wheel speed sensor 
<FL> connector terminal No. 1, and between A-05 
ASC-ECU connector terminal No. 46 and A-11 wheel speed 
sensor <FL> connector terminal No. 2

• Short circuit check of wheel speed sensor <FL> circuit

Q: Is the check result normal?

YES : Replace the wheel speed sensor <FL>. (Refer to 

P.35C-274

.) Then go to Step 13.

NO :  Repair the wiring harness. Then go to Step 13.

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 
ASC-ECU-side connector and the wiring harness-side 
connector, and then measure at the special tool connector 
side.

(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. 45 and 
the body ground.

OK: System voltage

Q: Is the check result normal?

YES : Go to Step 9.
NO :  Go to Step 11.

STEP 9. Wiring harness check between A-05 ASC-ECU 
connector terminal No. 45 and A-11 wheel speed sensor 
<FL> connector terminal No. 1, and between A-05 
ASC-ECU connector terminal No. 46 and A-11 wheel speed 
sensor <FL> connector terminal No. 2

• Open circuit check of wheel speed sensor <FL> circuit

Q: Is the check result normal?

YES : Go to Step 10.
NO :  Repair the wiring harness. Then go to Step 13.

AC400817CD

ASC-ECU

MB991997

Check harness

A-05 ASC-ECU
harness connector