Mitsubishi Galant (2004+). Manual - part 720

MANUAL A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-19

DIAGNOSIS

Required Special Tool:

•  MB991958: Scan Tool (MUT-III Sub Assembly)

• MB991824: Vehicle Communication Interface (V.C.I.)

• MB991827: MUT-III USB Cable

• MB991910: MUT-III Main Harness A (Vehicles with CAN 

communication system)

STEP 1. Using scan tool MB991958, diagnose the CAN bus 
line.

Use scan tool MB991958 to diagnose the CAN bus lines.
(1) Connect scan tool MB991958 to the data link connector.
(2) Turn the ignition switch to "ON" position.

(3) Diagnose the CAN bus line.
Q: Is the check result satisfactory?

YES : Go to Step 2.
NO :  Repair the CAN bus lines. Repair the CAN bus lines 

(Refer to GROUP 54C, Diagnosis-Can Bus 
Diagnostic Chart 

P.54C-621

). Then go to Step 7.

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 check result satisfactory?

YES : It can be assumed that this malfunction is intermittent. 

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

− How to 

Use Troubleshooting/Inspection Service Points 

P.00-6

.

NO :  Go to Step 3. 

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

MANUAL A/C DIAGNOSIS

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HEATER, AIR CONDITIONING AND VENTILATION

55A-20

STEP 3. Using scan tool MB991958, check data list item 03: 
air thermo sensor.

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 to the data link connector.
(2) Ignition switch: ON
(3) Set scan tool MB991958 to the data reading mode for item 

03: air thermo sensor.

• Check that the passenger room temperature matches 

the displayed value on the scan tool while the engine is 
cold.

NOTE: When this DTC is set and the system is fail-safe sta-
tus, the value of service data displays 

−

6

°

C.

(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor within the specified range?

YES : Replace the A/C-ECU. Then go to Step 7.
NO :  Go to Step 4.

STEP 4. Check A/C-ECU connector C-10 and air thermo 
sensor connector C-126 for loose, corroded or damaged 
terminals, or terminals pushed back in the connector.

Q: Are A/C-ECU connector C-10 and air thermo sensor 

connector C-126 in good condition?
YES : Go to Step 5.
NO :  Repair or replace the connector. Refer to GROUP 

00E, Harness Connector Inspection 

P.00E-2

. Then go 

to Step 7.

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

AC305231

CONNECTOR: C-126

CB

HARNESS SIDE

AC305233AW

CONNECTOR: C-10

HARNESS SIDE

C-10 (B)

MANUAL A/C DIAGNOSIS

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HEATER, AIR CONDITIONING AND VENTILATION

55A-21

STEP 5. Check the wiring harness between A/C-ECU 
connector C-10 (terminal 10 and 13) and air thermo sensor 
connector C-126 (terminals 2 and 1).

NOTE: Also check joint connector C-03 for loose, corroded, or 
damaged terminals, or terminals pushed back in the connector. 
If joint connector C-03 is damaged, repair or replace the con-
nector as described in GROUP 00E, Harness Connector 
Inspection 

P.00E-2

.

Q: Is the wiring harness between A/C-ECU connector C-10 

(terminal 10 and 13) and air thermo sensor connector 
C-126 (terminals 2 and 1) in good condition?
YES : Go to Step 6.
NO :  Repair the wiring harness. Then go to Step 7.

AC305233AW

CONNECTOR: C-10

HARNESS SIDE

C-10 (B)

AC305232

C-03

C-126

C-03

HARNESS SIDE

C-126

AP

CONNECTORS: C-03, C-126

MANUAL A/C DIAGNOSIS

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HEATER, AIR CONDITIONING AND VENTILATION

55A-22

STEP 6. Check the air thermo sensor.

(1) Disconnect the air thermo sensor connector C-126.

(2) Measure the resistance between connector terminals 1 and 

2 under at least two different temperatures. The resistance 
values should generally match those in the graph. 
NOTE: The temperature at the check should not exceed the 
range in the graph. 

Q: Is the air thermo sensor in good condition?

YES : Replace the A/C-ECU. Then go to Step 7.
NO :  Replace the air thermo sensor. Then go to Step 7.

STEP 7. 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 check result satisfactory?

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

AC305231

CONNECTOR: C-126

CB

HARNESS SIDE

AC001043

RESISTANCE k

Ω

8

6

4

2

0

-10

0

 10

 20

 30

   40

TEMPERATURE ˚C(˚F)

AB

(14)

(32)

(50)

(86)

(104)

(68)

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827