Mitsubishi Lancer (4A9 engine). Manual - part 44

TROUBLESHOOTING

ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-29

DIAGNOSTIC PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnosis
Use M.U.T.-III to 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 

− CAN Bus Diagnostics Table ). On 

completion, go to Step 2.

STEP 2. Diagnosis code recheck after resetting 
CAN bus lines

Q: Is the diagnosis code No. C1020 set?

YES : 

Go to Step 3.

NO : 

This diagnosis is complete.

STEP 3. M.U.T.-III data list
Check the following data list (Refer to 

P.35C-172

).

• Item No.03: RL wheel speed sensor

Q: Is the check result normal?

YES : 

Go to Step 12.

NO : 

Go to Step 4.

STEP 4. Voltage measurement at the A-58 ASC-
ECU connector

AC606869DC

ASC-ECU

MB991997

Check harness

A-58 ASC-ECU
harness connector

(1) Disconnect the ASC-ECU connector, connect 

special tool ASC check harness (MB991997) to 
the harness-side connector, and then measure 
the voltage 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 rear wheel 

speed sensor <LH> power supply terminal (signal 
terminal) No.36 and the body earth, and between 
the rear wheel speed sensor <LH> earth terminal 
No.37 and the body earth.

OK: 1 V or less

Q: Is the check result normal?

YES : 

Go to Step 5.

NO (Not normal at the terminal No.36 or No.37) : 

Go to Step 6.

STEP 5. Resistance measurement at A-58 ASC-
ECU connector

AC606869DD

ASC-ECU

MB991997

Check harness

A-58 ASC-ECU
harness connector

(1) Disconnect the ASC-ECU connector, connect 

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

(2) Measure the resistance between the rear wheel 

speed sensor <LH> earth terminal No.36 and the 
body earth, and between the rear wheel speed 
sensor <LH> earth terminal No.37 and the body 
earth.

OK: No continuity

Q: Is the check result normal?

TROUBLESHOOTING

ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-30

YES : 

Go to Step 8.

NO (Not normal at the terminal No.36 or No.37) : 

Go to Step 6.

STEP 6. Connector check: A-58 ASC-ECU 
connector, C-31 intermediate connector, D-17 
intermediate connector, F-24 rear wheel speed 
sensor <LH> 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-58 
ASC-ECU connector terminal No.36 and F-24 rear 
wheel speed sensor <LH> connector terminal 
No.1, and between A-58 ASC-ECU connector 
terminal No.37 and F-24 rear wheel speed sensor 
<LH> connector terminal No.2.

• Check for short circuit in rear wheel speed sensor 

<LH> circuit

Q: Is the check result normal?

YES : 

Replace the wheel speed sensor <RL> 

(Refer to 

P.35C-188

). Then go to Step 13.

NO : 

Repair the wiring harness. Then go to Step 
13.

STEP 8. Voltage measurement at the A-58 ASC-
ECU connector

AC606870BN

ASC-ECU

MB991997

Check harness

A-58 ASC-ECU
harness connector

(1) Disconnect the ASC-ECU connector, connect 

special tool ASC check harness (MB991997) to 
the ASC-ECU-side connector and harness-side 
connector, and then measure the voltage at the 
special tool connector side.

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

speed sensor <LH> circuit power supply terminal 
(signal terminal) No.36 and the body earth.

OK: Approximately 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-58 
ASC-ECU connector terminal No.36 and F-24 rear 
wheel speed sensor <LH> connector terminal 
No.1, and between A-58 ASC-ECU connector 
terminal No.37 and F-24 rear wheel speed sensor 
<LH> connector terminal No.2.

• Check for open circuit in rear wheel speed sensor 

<LH> circuit

Q: Is the check result normal?

YES : 

Go to Step 10.

NO : 

Repair the wiring harness. Then go to Step 
13.

STEP 10. Check for wheel speed sensor <RL> as 
a single unit
Refer to 

P.35C-188

.

Q: Is the check result normal?

YES : 

Go to Step 11.

NO : 

Replace the wheel speed sensor <RL> 
(Refer to 

P.35C-188

). Then go to Step 13.

STEP 11. Connector check: A-58 ASC-ECU 
connector, C-31 intermediate connector, D-17 
intermediate connector, F-24 rear wheel speed 
sensor <LH> connector

Q: Is the check result normal?

YES : 

Go to Step 12.

NO : 

Repair the defective connector. Then go to 
Step 13.

STEP 12. Check whether the diagnosis code is 
reset.
(1) Erase the diagnosis code.
(2) Drive the vehicle at 20 km/h or higher.

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

Q: Is the diagnosis code No. C1020 set?

TROUBLESHOOTING

ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-31

YES : 

Replace the hydraulic unit (integrated with 

ASC-ECU) (Refer to 

P.35C-185

). Then go 

to Step 13.

NO : 

Intermittent malfunction (Refer to GROUP 
00 

− How to Use Troubleshooting/How to 

Cope with Intermittent Malfunctions ).

STEP 13. Check whether the diagnosis code is 
reset.
(1) Erase the diagnosis code.

(2) Drive the vehicle at 20 km/h or higher.

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

Q: Is the diagnosis code No. C1020 set?

YES : 

Return to Step 1.

NO : 

This diagnosis is complete.

Code No. C102B Abnormality in RR wheel speed sensor circuit

Wheel Speed Sensor Circuit

ASC-ECU

(LH)

(LH)

(RH)

(RH)

FRONT WHEEL SPEED SENSOR

REAR WHEEL SPEED SENSOR

Wire colour code 
B : Black     LG : Light green     G : Green     L : Blue     W : White     Y : Yellow     SB : Sky blue 
BR : Brown     O : Orange     GR : Grey     R : Red     P : Pink     V : Violet     PU : Purple     SI : Silver

ACB02565

AC612691

AO

Connector: A-58 <LHD>

A-58 (B)

AC701238 AF

Connector: A-58 <RHD>

A-58 (B)

ACB02572

AB

Connector: C-67 <LHD>

ACA00895

ACA00895AT

Connector: C-67 <RHD>

AC612723

AL

Connector: D-12

AC612744 BI

Connector: F-04 <LANCER>

     (B)

AC801775BN

 (B)

Connector: F-04 <LANCER SPORTBACK>

TROUBLESHOOTING

ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-32

CAUTION

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

an incorrect diagnosis code may be set. Prior 
to this diagnosis, diagnose the CAN bus lines 
(Refer to GROUP 54C 

− CAN Bus Diagnostics 

Table ).

• Whenever ECU is replaced, ensure that the 

CAN bus lines are normal.

• When the hydraulic unit (integrated with ASC-

ECU) is replaced, always carry out the calibra-
tion of the steering wheel sensor, the G and 
yaw rate sensor and brake fluid pressure sen-
sor (Refer to 

P.35C-182

, 

P.35C-183

 and 

P.35C-

184

).

OPERATION

• The wheel speed sensor is a kind of a pulse gen-

erator. It consists of encoders (a plate on which 
north and south pole sides of the magnets are 
arranged alternately) for detecting the wheel 
speed which rotates at the same speed of the 
wheels and wheel speed sensors. This sensor 
outputs frequency pulse signals in proportion to 
the wheel speed.

• The pulse signals, which the wheel speed sensor 

creates, are sent to ASC-ECU. ASC-ECU uses 
the frequency of the pulse signals to determine 
the wheel speed.