Mitsubishi Colt Ralliart. Manual - part 627

TROUBLESHOOTING

ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-53

Code No. C1278: Valve relay stuck OFF

CAUTION

If there is any problem in the CAN bus lines, an 
incorrect diagnosis code may be set. Prior to this 
diagnosis, always diagnose the CAN bus lines.

OPERATION

• ASC-ECU contains the power supply circuit (ter-

minal No. 44) for the solenoid valve. The solenoid 
valve is energised by the valve relay, which is 
incorporated in ASC-ECU.

• The valve relay, which is incorporated in 

ASC-ECU, is always energising the solenoid 
valve unless the initial check is in progress when 
the ignition switch is turned on, or the recurrent 
system check is in progress.

DIAGNOSIS CODE SET CONDITIONS

When the solenoid valve is not energised even after 
the valve relay is turned ON, the ECU determines 
that the valve relay stuck OFF and sets this diagno-
sis code.

PROBABLE CAUSES

Current trouble

• Damaged wiring harness and connectors

• The ABS-ECU is defective.

Hydraulic unit (Motor and Solenoid Valve) Circuit

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

FUSIBLE 
LINK

FUSIBLE 
LINK

3

5

ASC-ECU

HYDRAULIC UNIT

SOLENOID
VALVE 
POWER 
SOURCE

ABS SOLENOID VALVE 

MOTOR

MOTOR 
POWER 
SOURCE

Main

Index

Group

TOC

TROUBLESHOOTING

ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-54

Past trouble

• Carry out diagnosis with particular emphasis on 

connector(s) or wiring harness between the 
power supply circuit (terminal No. 44) to the 
ASC-ECU solenoid valve or earth circuit (terminal 
No. 46). For diagnosis procedures, refer to How 
to treat past trouble (GROUP 00 

− How to Use 

Troubleshooting/Inspection Service Points 

P.00-13

).

DIAGNOSTIC PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostics
Use the 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 
54D 

− Troubleshooting 

P.54D-13

.) On 

completion, go to Step 2.

STEP 2. Diagnosis code recheck after resetting 
CAN bus lines

Q: Is the diagnosis code No. C1278 set?

YES : 

Go to Step 3.

NO : 

This diagnosis is complete.

STEP 3. Connector check: A-05 ASC-ECU 
connector

Q: Is the check result normal?

YES : 

Go to Step 4.

NO : 

Repair the damaged connector.

STEP 4. Measure the resistance at A-05 ASC-ECU 
connector.

(1) Disconnect the connector, connect the ABS 

check harness (Special tool: MB991984) to the 
harness-side connector, and measure the voltage 
at the special tool connector side.
NOTE: Do not connect the special tool to 
ASC-ECU.

(2) Measure the resistance between the terminal No. 

44 and the positive battery terminal.

OK: Continuity exists (2 

Ω or less)

Q: Is the check result normal?

YES : 

Go to Step 5.

NO : 

Repair the wiring harness between the 
terminal No. 44 and the positive battery 
terminal.

AC601083

Connector: A-05

AB

A-05(Black)

Harness side

AC601083

Connector: A-05

AB

A-05(Black)

Harness side

AC601085AF

MB991984

ASC-ECU

ASC-ECU harness connector

Check connector

Main

Index

Group

TOC

TROUBLESHOOTING

ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-55

STEP 5. Diagnosis code recheck
Recheck if the diagnosis code is set.
(1) Erase the diagnosis code.
(2) Ignition switch: LOCK (OFF) position
(3) Ignition switch: ON

Q: Is the diagnosis code No. C1278 set?

YES : 

Replace the ASC-ECU.

NO : 

Intermittent malfunction (Refer to GROUP 
00 

− How to Cope with Intermittent 

Malfunction 

P.00-13

.)

Code No. C1279: Valve relay stuck ON

CAUTION

If there is any problem in the CAN bus lines, an 
incorrect diagnosis code may be set. Prior to this 
diagnosis, always diagnose the CAN bus lines.

OPERATION

• ASC-ECU contains the power supply circuit (ter-

minal No. 44) for the solenoid valve. The solenoid 
valve is energised by the valve relay, which is 

incorporated in ASC-ECU.

• The valve relay, which is incorporated in 

ASC-ECU, is always energising the solenoid 
valve unless the initial check is in progress when 
the ignition switch is turned on, or the recurrent 
system check is in progress.

Hydraulic unit (Motor and Solenoid Valve) Circuit

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

FUSIBLE 
LINK

FUSIBLE 
LINK

3

5

ASC-ECU

HYDRAULIC UNIT

SOLENOID
VALVE 
POWER 
SOURCE

ABS SOLENOID VALVE 

MOTOR

MOTOR 
POWER 
SOURCE

Main

Index

Group

TOC

TROUBLESHOOTING

ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-56

DIAGNOSIS CODE SET CONDITIONS

ASC-ECU monitors the power supply voltage to the 
solenoid valve. If the solenoid valve is still energised 
even after the valve relay is turned OFF, the ECU 
determines that the motor relay stuck OFF, and sets 
this diagnosis code.

Current trouble

• Damaged wiring harness and connectors

• The ABS-ECU is defective.

DIAGNOSTIC PROCEDURE

STEP 1. M.U.T.-III CAN bus diagnostics
Use the 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 
54D 

− Troubleshooting 

P.54D-13

.) On 

completion, go to Step 2.

STEP 2. Diagnosis code recheck after resetting 
CAN bus lines

Q: Is the diagnosis code No. C1279 set?

YES : 

Go to Step 3.

NO : 

This diagnosis is complete.

STEP 3. Connector check: A-05 ASC-ECU 
connector

Q: Is the check result normal?

YES : 

Go to Step 4.

NO : 

Repair the damaged connector.

STEP 4. Measure the resistance at A-05 ASC-ECU 
connector.

(1) Disconnect the connector, connect the ABS 

check harness (Special tool: MB991984) to the 
harness-side connector, and measure the voltage 
at the special tool connector side.
NOTE: Do not connect the special tool to 
ASC-ECU.

(2) Measure the resistance between the terminal No. 

44 and the positive battery terminal.

OK: Continuity exists (2 

Ω or less)

Q: Is the check result normal?

YES : 

Go to Step 5.

NO : 

Repair the wiring harness between the 
terminal No. 44 and the positive battery 
terminal.

AC601083

Connector: A-05

AB

A-05(Black)

Harness side

AC601083

Connector: A-05

AB

A-05(Black)

Harness side

AC601085AF

MB991984

ASC-ECU

ASC-ECU harness connector

Check connector

Main

Index

Group

TOC