Mitsubishi Evolution X. Manual - part 780

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-127

DTC SET CONDITIONS

This diagnostic trouble code is set under the cases below.

• The power supply voltage of pump motor, which is not in 

operation, is abnormally low for a prolonged period.

• The voltage of pump motor, which is not in operation, is 

abnormally high for a prolonged period.

.

PROBABLE CAUSES

Current trouble

• Fusible link malfunction

• Damaged wiring harness and connectors

• Abnormality in battery or generator

• ASC-ECU malfunction

Past trouble

• Perform the diagnosis with a particular emphasis on the wir-

ing harness and connector failures in the ASC-ECU motor 
power supply circuit (A-05 ASC-ECU connector terminal 
No. 1) and in the ground circuit (A-05 ASC-ECU connector 
terminal No. 16 and No.47). 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 C2116 set?

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

STEP 3. Fusible link check: Check the fusible link No.26.
Q: Is the check result normal?

YES : Go to Step 4.
NO :  Replace the fusible link No.26.

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-128

STEP 4. Battery check
Refer to GROUP 54A 

− Battery Test 

P.54A-9

.

Q: Is the battery in good condition?

YES : Go to Step 5.
NO :  Charge or replace the battery.

STEP 5. Charging system check
Refer to GROUP 16 

− Output Current Test 

P.16-8

.

Q: Is the charging system in good condition?

YES : Go to Step 6.
NO :  Repair or replace the charging system component(s).

STEP 6. Voltage measurement at the A-05 ASC-ECU 
connector
(1) Disconnect the connector, connect the ASC check harness 

(Special tool: MB991997) to the wiring 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 voltage between the terminal No. 1 and the 

body ground.

OK: System voltage

Q: Is the check result normal?

YES : Go to Step 8.
NO :  Go to Step 7.

STEP 7. Connector check: A-05 ASC-ECU connector
Q: Is the check result normal?

YES : An open or short circuit may be present in the pump 

motor power supply circuit. Repair the wiring harness 
between A-05 ASC-ECU connector terminal No. 1 
and the fusible link No. 26.

NO  :  Repair the defective connector.

AC400817CP

ASC-ECU

MB991997

A-05 ASC-ECU 
harness connector

Check harness

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-129

STEP 8. Resistance measurement at A-05 ASC-ECU 
connector
(1) Disconnect the connector, connect the ASC check harness 

(Special tool: MB991997) to the wiring 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. 16 and 

the body ground as well as between the terminal No. 47 
and the body ground.

OK: Continuity exists (2 

Ω or less)

Q: Is the check result normal?

YES : Go to Step 10.
NO :  Go to Step 9.

STEP 9. Connector check: A-05 ASC-ECU connector
Q: Is the check result normal?

YES : An open circuit may be present in the ground circuit. 

Repair the wiring harness between A-05 ASC-ECU 
connector terminal No. 16 and the ground as well as 
between A-05 ASC-ECU connector terminal No. 47 
and the ground.

NO  :  Repair the defective connector.

STEP 10. 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 C2116 set?

YES : Replace the hydraulic unit (incorporates in 

ASC-ECU).(Refer to 

P.35C-272

.) Then go to Step 11.

NO :  Intermittent malfunction. (Refer to GROUP 00 

− How 

to Cope with Intermittent Malfunction 

P.00-15

.)

AC400817CO

ASC-ECU

MB991997

A-05 ASC-ECU 
harness connector

Check harness

DIAGNOSIS

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ACTIVE SKID CONTROL SYSTEM (ASC)

35C-130

STEP 11. 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 C2116 set?

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

DTC C121D: Abnormality in brake fluid pressure 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

The pressure sensor is incorporated in the hydraulic unit. When 
the brake pedal is depressed, the pressure sensor detects the 
brake pressure applied from the master cylinder, converts this 
pressure into the voltage signal, and then outputs the signal.

.

DTC SET CONDITIONS

If the pressure sensor output signal is outside the standard 
value range, this diagnostic trouble code is set.

.

PROBABLE CAUSES

• Incorrect brake pedal height

• Incorrect adjustment of stoplight switch

• Master cylinder malfunction

• Brake booster malfunction

• ASC-ECU malfunction

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