Mitsubishi Montero (2004+). Manual - part 632

AUTO A/C DIAGNOSIS

TSB Revision

AUTOMATIC AIR CONDITIONING

55B-17

DTC 21, 22: A/C sensor System

.

DTC SET CONDITION

• DTC 21 is set if there is a defective connector 

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

• DTC 22 is set if there is a short circuit in the A/C 

sensor input circuit.

.

TROUBLESHOOTING HINT

• Malfunction of connector.

• Malfunction of the harness.

• Malfunction of the A/C sensor.

• Malfunction of the A/C-ECU.

DIAGNOSIS

Required Special Tools:

• MB991223: Harness Set

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

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

• MB991827: MUT-III USB Cable

• MB991911: MUT-III Main Harness B (Vehicles without 

CAN communication system)

A/C SENSOR

A/C-ECU

SIGNAL INPUT
CIRCUIT

Air Thermo Sensor Circuit

AC001535AF

CONNECTORS: D-21, D-24

D-21

D-24

AUTO A/C DIAGNOSIS

TSB Revision

AUTOMATIC AIR CONDITIONING

55B-18

STEP 1. Using scan tool MB991958, check data list item 21: 
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.
Check the data list. 
Item 21: Air thermo sensor
Q: Are the evaporator blowout temperature and indicated 

temperature on scan tool MB991958 almost equal?
YES :  It can be assumed that this malfunction is intermittent 

(Refer to GROUP 00 - How to Cope with Intermittent 
Malfunction). 

NO :   Go to Step 2.

STEP 2. Check the A/C sensor.

 When the resistance between the sensor terminals is mea-
sured at two or more temperature conditions, the resistance 
should satisfy the value shown in the illustration.
NOTE: The temperature conditions at the check shall be within 
the range shown in the characteristic diagram.
Q: Is the check result normal? 

YES : Go to Step 3.
NO :  Replace the A/C sensor. Then go to Step 5.

AC307591 AB

MB991911

DATA LINK

CONNECTOR

MB991824

MB991827

AC204170

CONNECTOR : D-21

CN

1
2

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)

AUTO A/C DIAGNOSIS

TSB Revision

AUTOMATIC AIR CONDITIONING

55B-19

STEP 3. Check A/C sensor connector D-21 and A/C-ECU 
connector D-24 for damage.

Q: Is A/C sensor connector D-21 and A/C-ECU connector 

D-24 in good condition?
YES : Go to Step 4.
NO :  Repair or replace the connector. Refer to GROUP 

00E, Harness Connector Inspection 

P.00E-2

. Then go 

to Step 5.

STEP 4. Check the wiring harness between A/C sensor 
connector D-21 (terminals 1 and 2) and A/C-ECU D-24 
(terminals 30 and 29).

Q: Is the wiring harness between A/C sensor connector 

D-21 (terminals 1 and 2) and A/C-ECU D-24 (terminals 30 
and 29) in good condition?
YES : Replace the A/C-ECU (Refer to 

P.55B-142

). Then go 

to Step 5.

NO :  Repair the wiring harness. Then go to Step 5.

AC204188

CONNECTORS : D-21, D-24

D-24(B)

D-24(B)

BZ

D-21

D-21

HARNESS SIDE

HARNESS SIDE

22

23

30

31

25

26

33

34

32

24

28

3635

27

29

21

1
2

AC204188

CONNECTORS : D-21, D-24

D-24(B)

D-24(B)

BZ

D-21

D-21

HARNESS SIDE

HARNESS SIDE

22

23

30

31

25

26

33

34

32

24

28

3635

27

29

21

1
2

AUTO A/C DIAGNOSIS

TSB Revision

AUTOMATIC AIR CONDITIONING

55B-20

STEP 5. Recheck for diagnostic trouble code.
Q: Is DTC 21 or 22 set?

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

DTC 31: Potentiometer System of Air Mixing Damper Control Motor Assembly

.

DTC SET CONDITION
DTC 31 is output if there is an open or short circuit in 
the potentiometer input circuit, or if there is an open 
circuit in the power circuit or earth circuit.

.

TROUBLESHOOTING HINT

• Malfunction of connector.

• Malfunction of the harness.

• Malfunction of the air mixing damper control 

motor and potentiometer.

• Malfunction of the A/C-ECU.

Air Mix Damper Motor Potentiometer Circuit

AC001535 AH

D-20

D-24

CONNECTORS: D-20, D-24