Mitsubishi Lancer Evolution X. Manual - part 192

DIAGNOSIS

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ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-233

SYMPTOM PROCEDURES

Inspection Procedure 1: The scan tool cannot communicate with the ABS/ASC system.

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.

• If the power is supplied with the ground circuit of CAN 

communication devices open circuited, a potential 
abnormality may occur to the connected CAN bus line.

• 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-287

, 

P.35C-289

, 

P.35C-294

, and 

P.35C-295

.)

.

TECHNICAL DESCRIPTION (COMMENT)

When the scan tool MB991958 cannot communicate with the 
ABS/ASC system, there may be a malfunction to the CAN bus 
lines, ASC-ECU power supply circuit, ground, or ASC-ECU.

.

PROBABLE CAUSES

• Damaged wiring harness and connectors
• ASC-ECU malfunction
• Wrong M.U.T.-III wiring harness
• Abnormality in battery or generator
• Abnormality in power supply voltage to ASC-ECU
• ECU malfunction of other system

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

Using scan tool MB991958, diagnose the CAN bus lines.
Using the scan tool, diagnose the CAN bus lines.
Q: Is the check result normal?

YES : Check and repair the power supply circuit system. ( 

Refer to 

P.35C-258

.)

NO :  Repair the CAN bus lines. (Refer to GROUP 54C − 

Troubleshooting 

P.54C-15

.)

DIAGNOSIS

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ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-234

Inspection Procedure 2: With the parking brake released, the brake warning light remains illuminated 
(ABS warning light is turned off).

CAN DRIVE 
CIRCUIT

INTERFACE 
CIRCUIT

ETACS-
ECU

JOINT CONNECTOR 
(CAN1)

BRAKE 
FLUID 
LEVEL 
SWITCH

PARKING 
BRAKE 
SWITCH

INTERFACE CIRCUIT

CPU

CAN 
TRANSCEIVER 
CIRCUIT

LED DRIVE 
CIRCUIT

COMBINATION 
METER

LCD

·BRAKE
·FUEL WARNING
·OIL

Brake Fluid Level Switch and Parking Brake Switch Circuit

DIAGNOSIS

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ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-235

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 commu-

nication circuit is normal.

.

CIRCUIT OPERATION

• When the parking brake switch is turned ON, the combina-

tion meter terminal No. 4 is grounded, and then the brake 
warning light is illuminated.

• When the brake fluid level drop is detected, the brake fluid 

level switch is turned from ON to OFF. ETACS-ECU moni-
tors the brake fluid level switch, and gives an instruction via 
the CAN bus line to the combination meter to illuminate the 
brake warning light.

.

PROBABLE CAUSES

• The brake pad thickness is at the limit value or less.
• The brake fluid amount is at the "LOWER" level or lower.
• Poor adjustment of the parking brake lever
• Damaged wiring harness and connectors
• Parking brake switch malfunction
• Brake fluid level switch malfunction
• Combination meter malfunction
• ETACS-ECU malfunction

AC708972AP

Connector: C-312

ETACS-ECU

AC708949

Connector: A-09

AF

AC708950

Connector: C-04

AR

AC708951AN

C-23

C-122

Connectors: C-23, C-122

DIAGNOSIS

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ACTIVE STABILITY CONTROL SYSTEM (ASC)

35C-236

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

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 2.
NO :  Repair the CAN bus lines. (Refer to GROUP 54C − 

Troubleshooting 

P.54C-15

.)

STEP 2. Scan tool diagnostic trouble code for other 
systems
Using scan tool MB991958, check if the diagnostic trouble 
code is set in the combination meter and ETACS-ECU.
Q: Is any DTC set?

YES : Carry out the diagnosis for the DTC.
NO :  Go to Step 3.

STEP 3. Brake fluid level check
Check that the brake fluid is filled up to the "MIN" level or 
higher.
Q: Is the check result normal?

YES : Go to Step 5.
NO :  Go to Step 4.

STEP 4. Brake pad check
Refer to GROUP 35A − On-vehicle Service, Brake Pad Check 

P.35A-18

.

Q: Is the check result normal?

YES : Fill the brake fluid up to the "MAX" level. Then go to 

Step 18.

NO :  Replace the brake pad. (Refer to GROUP 35A − 

On-vehicle Service, Brake Pad Replacement 

P.35A-18

.) Then, go to Step 18.

STEP 5. Brake fluid level switch check
Refer to GROUP 35A − On-vehicle Service, Brake Fluid Level 

Switch Check 

P.35A-17

.

Q: Is the check result normal?

YES : Go to Step 6.
NO :  Replace the reservoir tank assembly. (Refer to 

GROUP 35A − Master Cylinder Assembly and Brake 

Booster Assembly 

P.35A-26

.) Then, go to Step 18.