Mitsubishi L200. Manual - part 870

TROUBLESHOOTING

AUTOMATIC AIR CONDITIONER

55B-9

DIAGNOSIS PROCEDURE

STEP 1. Connector check: A-139 ambient 
temperature sensor connector and C-44 A/C-ECU 
connector

AC509975

A-139 (B)

AL

Harness side

Connector: A-139

AC509611BM

Harness side

Connector: C-44 <LHD>

AC509932BU

Harness side

Connector: C-44 <RHD>

Q: Is the check result normal?

YES : 

Go to Step 2.

NO : 

Repair the connector.

TROUBLESHOOTING

AUTOMATIC AIR CONDITIONER

55B-10

STEP 2. Check the wiring harness between A-139 
ambient temperature sensor connector 
(terminals 1 and 2) and C-44 A/C-ECU connector 
(terminals 38 and 31).

AC509975

A-139 (B)

AL

Harness side

Connector: A-139

AC509612AH

C-44

C-44

Harness side

C-138 (L)

C-137, C-138

C-33

C-137 (L)

C-33

Connectors: C-33, C-44, C-137, C-138 <LHD>

AC509930 AY

Connector: C-33 <RHD>

NOTE: 

AC509932DN

Harness side

Connectors: C-44, C-137, C-138 <RHD>

C-44

C-137 (L)

C-138 (L)

C-44

C-137, C-138

Prior to the wiring harness inspection, check interme-
diate connector C-33, joint connectors C-137 and C-
138, and repair if necessary.

• Check the sensor signal line and earth line for 

open and short circuit.

Q: Is the check result normal?

YES : 

Go to Step 3.

NO : 

Repair the wiring harness.

STEP 3. Check the ambient temperature sensor.
Refer to 

P.55B-99

.

Q: Is the check result normal?

YES : 

Go to Step 4.

NO : 

Replace the ambient temperature sensor.

STEP 4. M.U.T.-III diagnosis code

Q: Is the diagnosis code set?

YES : 

Replace the automatic A/C control panel (A/

C-ECU).

NO : 

The trouble can be an intermittent 
malfunction (Refer to GROUP 00, How to 
Cope with Intermittent Malfunction ).

TROUBLESHOOTING

AUTOMATIC AIR CONDITIONER

55B-11

Code No. B1021,B1022: Air Thermo Sensor system

Air Thermo Sensor Circuit

AIR THERMO
SENSOR

A/C-ECU

Wire colour code
B : Black     LG : Light green     G : Green     L : Blue     W : White     Y : Yellow     SB : Sky blue
BR : Brown     O : Orange     GR : Grey     R : Red     P : Pink     V : Violet     PU : Purple

COMMENTS ON TROUBLE SYMPTOM
This code is set when the air thermo sensor circuit is 
open (Code No.B1022) or is short (Code No.B1021).

PROBABLE CAUSES

• Malfunction of the air thermo sensor

• Damaged the wiring harness or connectors

• Malfunction of the automatic A/C control panel (A/

C-ECU)

DIAGNOSIS PROCEDURE

STEP 1. Connector check: C-44 A/C-ECU 
connector and C-45 air thermo sensor connector

AC509611BT

Harness side

C-44

C-45

C-44

Harness side

Connectors: C-44, C-45 <LHD>

C-45

AC509932 BX

Harness side

C-44

C-45

C-44

Harness side

Connectors: C-44, C-45 <RHD>

C-45

Q: Is the check result normal?

YES : 

Go to Step 2.

NO : 

Repair the connector.

TROUBLESHOOTING

AUTOMATIC AIR CONDITIONER

55B-12

STEP 2. Check the wiring harness between C-44 
A/C-ECU connector (terminals 39 and 38) and C-
45 air thermo sensor connector (terminals 2 and 
1).

AC509612AC

Harness side

C-44

C-45

C-44

Harness side

Connectors: C-44, C-45, C-138 <LHD> C-45

C-138 (L)

C-138

AC509933AB

Harness side

C-44

C-45

C-44

Harness side

C-45

C-138 (L)

C-138

Connectors: C-44, C-45, C-138 <RHD>

NOTE: Prior to the wiring harness inspection, check 
joint connector C-138, and repair if necessary.

• Check the sensor signal line and earth line for 

open and short circuit.

Q: Is the check result normal?

YES : 

Go to Step 3.

NO : 

Repair the wiring harness.

STEP 3. Replace the A/C evaporator air outlet 
thermistor, and then recheck the trouble 
symptom.
 Check that the A/C works normally.

Q: Is the check result normal?

YES : 

This diagnosis is complete.

NO : 

Go to Step 4.

STEP 4. M.U.T.-III diagnosis code

Q: Is the diagnosis code set?

YES : 

Replace the automatic A/C control panel (A/

C-ECU).

NO : 

The trouble can be an intermittent 
malfunction (Refer to GROUP 00, How to 
Cope with Intermittent Malfunction ).