Mitsubishi Galant (2004+). Manual - part 732

MANUAL A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-67

DTC B1021, B1022: Air Thermo Sensor System

.

DTC SET CONDITION

• DTC B1021 is set if there is a short circuit in the 

air thermo sensor input circuit.

• DTC B1022 is set if there is a defective connector 

connection, or if there is an open circuit in the 
harness.

.

TECHNICAL DESCRIPTION (COMMENT)

Current trouble

• The A/C-ECU, the air thermo sensor, or connec-

tor(s) or wiring between the two may be defec-
tive.

Past trouble

• If DTC B1021 or B1022 is stored as a past trou-

ble, carry out diagnosis with particular emphasis 
on wiring and connector(s) between the A/C-ECU 
and the air thermo 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 air thermo sensor.

• Malfunction of the A/C-ECU.

A/C-ECU

JOINT
CONNECTOR (2)

AIR THERMO
SENSOR

Air Thermo Sensor Circuit

AC305233

C-16 (B)

C-15 (B)

CONNECTORS: C-15, C-16

BE

AC305231

CONNECTOR: C-03, C-126

CC

C-126

C-03

MANUAL A/C DIAGNOSIS

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55A-68

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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55A-69

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.

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

MANUAL A/C DIAGNOSIS

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STEP 4. Check A/C-ECU connectors C-15, C-16 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 connectors C-15, C-16 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.

AC305234

CONNECTORS: C-15, C-16

C-16 (B)

HARNESS SIDE

C-16

C-15

C-15 (B)

HARNESS SIDE

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

AG

AC305231

CONNECTOR: C-126

CB

HARNESS SIDE