Mitsubishi Montero (2002-2004). Manual - part 80

AUTO A/C DIAGNOSIS

TSB Revision

AUTOMATIC AIR CONDITIONING

55B-13

STEP 1. Using scan tool MB991502, check data list item 15: 
Heater water temperature sensor.
Check the data list.
Item 15: Heater water temperature sensor
Q: Are the heater core wall temperature and indicated 

temperature on scan tool MB991502 almost equal?
YES :  It can be assumed that this malfunction is 

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

P.00-6

.)

NO :   Go to Step 2.

STEP 2. Check the heater water temperature sensor.
 When the resistance between the heater water temperature 
sensor terminals is measured at two or more temperature con-
ditions, the measured 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 heater water temperature sensor. Then 

go to Step 5.

AC204170

CONNECTOR : D-19

CL

2 1

HARNESS 
SIDE

ACX00826AB

RESISTANCE
   (k

Ω

)

TEMPERATURE ˚C(˚F)

20

25

30

15

10

5

0

0

20

40

60

80

100

-10

(32)

(68)

(104)

(140) (176) (212)

(14)

AUTO A/C DIAGNOSIS

TSB Revision

AUTOMATIC AIR CONDITIONING

55B-14

STEP 3. Check heater water temperature sensor connector 
D-19 and A/C-ECU connector D-24 for damage.
Q: Is heater water temperature sensor connector D-19 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 heater water 
temperature sensor connector D-19 (terminals 1 and 2) and 
A/C-ECU D-24 (terminals 23 and 29).
Q: Is the wiring harness between heater water temperature 

sensor connector D-19 (terminals 1 and 2) and A/C-ECU 
D-24 (terminals 23 and 29) in good condition?
YES : Replace the A/C-ECU. (Refer to 

P.55B-136

.) Then go 

to Step 5.

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

AC204188

CONNECTORS : D-19, D-24

D-24(B)

D-24(B)

BX

D-19

D-19

HARNESS SIDE

HARNESS SIDE

2 1

22

23

30

31

25

26

33

34

32

24

28

3635

27

29

21

AC204188

CONNECTORS : D-19, D-24

D-24(B)

D-24(B)

BX

D-19

D-19

HARNESS SIDE

HARNESS SIDE

2 1

22

23

30

31

25

26

33

34

32

24

28

3635

27

29

21

AUTO A/C DIAGNOSIS

TSB Revision

AUTOMATIC AIR CONDITIONING

55B-15

STEP 5. Recheck for diagnostic trouble code.
Q: Is DTC 15 or 16 set?

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

DTC 21, 22: Air Thermo Sensor System

DTC SET CONDITION

• DTC 21 is output if there is a defective connector 

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

• DTC 22 is output if there is a short circuit in the 

air thermo sensor input circuit.

TROUBLESHOOTING HINT

• Malfunction of connector.

• Malfunction of the harness.

• Malfunction of the air thermo sensor.

• Malfunction of the A/C-ECU.

Air Thermo Sensor Circuit

AC205350

AC001535AF

CONNECTORS: D-21, D-24

D-21

D-24

AUTO A/C DIAGNOSIS

TSB Revision

AUTOMATIC AIR CONDITIONING

55B-16

STEP 1. Using scan tool MB991502, check data list item 21: 
Air thermo sensor.
Check the data list. 
Item 21: Air thermo sensor
Q: Are the evaporator blowout temperature and indicated 

temperature on scan tool MB991502 almost equal?
YES :  It can be assumed that this malfunction is 

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

P.00-6

.) 

NO :   Go to Step 2.

STEP 2. Check the air thermo 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 air thermo sensor. Then go to Step 5.

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)