Mitsubishi Evolution X. Manual - part 1270

AUTO A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55-31

TROUBLESHOOTING HINT

• Malfunction of connector.

• Malfunction of the harness.

• Malfunction of the ambient air temperature sensor.

• Malfunction of the A/C-ECU.

DIAGNOSIS

Required Special Tool:

•  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 
line

CAUTION

To prevent damage to scan tool MB991958, always turn the 
ignition switch to the "LOCK" (OFF) position before con-
necting or disconnecting scan tool MB991958.
(1) Connect scan tool MB991958. Refer to "How to connect the 

Scan Tool (M.U.T.-III) 

P.55-7

."

(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the CAN bus line found to be normal?

YES : Go to Step 2.
NO :  Repair the CAN bus line. (Refer to GROUP 54C, 

Diagnosis 

P.54C-14

).

STEP 2. Recheck for diagnostic trouble code.
Recheck if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to "ON" position.
(3) Check if the DTC is set.
Q: Is the DTC set?

YES : Go to Step 3. 
NO :  It can be assumed that this malfunction is intermittent. 

Refer to GROUP 00, How to Use 
Troubleshooting/Inspection Service Points 

− How to 

Cope with Intermittent Malfunctions 

P.00-15

.

AC608435

Data link connector

MB991827

MB991824

MB991910

AB

AUTO A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55-32

STEP 3. Check ambient air temperature sensor connector 
A-49 and ETACS-ECU connector C-312 for loose, corroded 
or damaged terminals, or terminals pushed back in the 
connector.
Q: Are ambient air temperature sensor connector A-49 and 

ETACS-ECU connector C-312 in good condition?
YES : Go to Step 4.
NO :  Repair or replace the connector. Refer to GROUP 

00E, Harness Connector Inspection 

P.00E-2

.

STEP 4. Check the wiring harness between ambient air 
temperature sensor connector A-49 (terminals 2 and 1) and 
ETACS-ECU connector C-312 (terminals 7 and 14).
Q: Is the wiring harness between ambient air temperature 

sensor connector A-49 (terminals 2 and 1) and 
ETACS-ECU connector C-312 (terminals 7 and 14) in 
good condition?
YES : Go to Step 5.
NO :  Repair the wiring harness.

STEP 5. Check the ambient air temperature sensor.
Measure the resistance between connector terminals 1 and 2 
under at least two different temperatures. The resistance val-
ues should generally match those in the graph. 
NOTE: The temperature at the check should not exceed the 
range in the graph. 
Q: Is the ambient air temperature sensor in good 

condition?
YES : Replace the A/C-ECU. Then go to Step 6.
NO :  Replace the ambient air temperature sensor. Then go 

to Step 6.

STEP 6. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Connect scan tool MB991958 to the data link connector
(2) Turn the ignition switch to the "ON" position.
(3) Check if the DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?

YES : Return to Step 1.
NO :  The procedure is complete.

AC209192

10

8

6

4

2

0

AB

10
(50)

30
(86)

Resistance

(k

Ω)

Temperature ºC (ºF)

  0
(32)

  40
(104)

-10
(14)

 20
(68)

AUTO A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55-33

DTC B1079: Refrigerant Leaks

A/C Pressure Sensor Circuit

A/C-ECU

JOINT
CONNECTOR (2)

A/C PRESSURE
SENSOR

AC708948

Connector: A-53

AF

A-53 (B)

AC708951AL

Connector: C-22

C-22 (B)

AC708950AQ

C-131

Connectors: C-102, C-131

C-102 (B)

AUTO A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55-34

.

DTC SET CONDITION

DTC B1079 will be set when the A/C pressure sensor detects 
the refrigerant pressure of specified level or less.
NOTE: When DTC B1079 is set, the A/C indicator of A/C con-
trol panel flashes.

.

TECHNICAL DESCRIPTION (COMMENT)

Current trouble

• The refrigerant amount is not at the specified level, or the 

wiring harness or connector between the A/C-ECU and A/C 
pressure sensor, and the A/C-ECU itself or A/C pressure 
sensor itself may have failed.

Past trouble

• If DTC B1079 is stored as a past trouble, carry out diagno-

sis with particular emphasis on wiring and connector(s) 
between the A/C-ECU and the A/C pressure sensor. If the 
connectors and wiring are normal, and obviously the ECU is 
the cause of the trouble, replace the ECU. If in doubt, do not 
replace the ECU.

.

TROUBLESHOOTING HINT

• Malfunction of connector.

• Malfunction of the harness.

• Malfunction of the A/C pressure sensor.

• Malfunction of the A/C-ECU.

DIAGNOSIS

Required Special Tool:

•  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