Mitsubishi L200. Manual - part 291

AC509934

Connectors: C-207, C-208 <LHD>

Junction block (Front view)

C-208

CX

Harness side

C-207

AC509936

Connectors: C-207, C-208 <RHD>

Harness side

C-208

C-207

BZ

Junction block 
(Front view)

TROUBLESHOOTING

AUTOMATIC TRANSMISSION

23A-71

OPERATION
If a fail-safe operation is activated, the A/T control 
relay shuts off the power supply to the solenoid valve 
in accordance with the signal from the A/T-ECU.

DIAGNOSIS CODE SET CONDITION
Code No.P1788 (P1751) will be set if the A/T control 
voltage is less than 7 V after the ignition switch is 
turned on.
If code No.P1788 (P1751) is set, the transmission 
will be held in 3rd gear.

PROBABLE CAUSES

• Malfunction of A/T control relay

• Damaged harness wires and connectors

• Malfunction of the A/T-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III data list
Item 08: Relay voltage (Refer to data list reference 
table 

P.23A-103

.)

Q: Is the check result normal?

YES : 

Intermittent malfunction (Refer to GROUP 

00 

− How to Cope with Intermittent 

Malfunction .)

NO : 

Go to Step 2.

STEP 2. Check the A/T control relay connector
Refer to 

P.23A-118

.

Q: Is the check result normal?

YES : 

Go to Step 3.

NO : 

Replace the A/T control relay.

STEP 3. Connector check: A-19X A/T control 
relay connector
Check for the contact with terminals.

Q: Is the check result normal?

YES : 

Go to Step 4.

NO : 

Repair the defective connector.

STEP 4. Measure the voltage at A/T control relay 
connector A-19X.
Disconnect the A/T control relay, and measure the 
voltage between terminal No.4 and earth at the relay 
box side.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 8.

NO : 

Go to Step 5.

STEP 5. Connector check: A-115 intermediate 
connector
Check for the contact with terminals.

Q: Is the check result normal?

YES : 

Go to Step 6.

NO : 

Repair the defective connector.

STEP 6. Check the harness between A/T control 
relay connector A-19X terminal No.4 and fusible 
link (23).
Check the power supply line for short or open circuit.

Q: Is the check result normal?

YES : 

Go to Step 7.

NO : 

Repair the wiring harness.

STEP 7. M.U.T.-III data list
Item 08: Relay voltage (Refer to data list reference 
table 

P.23A-103

.)

Q: Is the check result normal?

YES : 

The trouble can be an intermittent 

malfunction (Refer to GROUP 00 

− How to 

Cope with Intermittent Malfunction ).

NO : 

Replace the A/T-ECU.

TROUBLESHOOTING

AUTOMATIC TRANSMISSION

23A-72

STEP 8. Measure the voltage at the A/T control 
relay connector A-19X.
(1) Turn the ignition switch to the ON position.
(2) Disconnect the A/T control relay, and measure 

the voltage between terminal No.1 and earth at 
the relay box side.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 11.

NO : 

Go to Step 9.

STEP 9. Connectors check: C-52 <4A/T, 5A/T-
LHD>or C-34 <5A/T-RHD> intermediate 
connector, C-208 J/B connector
Check for the contact with terminals.

Q: Is the check result normal?

YES : 

Go to Step 10.

NO : 

Repair the defective connector.

STEP 10. Check the wiring harness between A/T 
control relay connector A-19X terminal No.1 and 
J/B connector C-208 terminal No.2.
Check the power supply line for short or open circuit.

Q: Is the check result normal?

YES : 

Go to Step 7.

NO : 

Repair the wiring harness.

STEP 11. Measure the voltage at A/T-ECU 
connector C-19.
(1) Install the A/T control relay.
(2) Turn the ignition switch to the ON position.
(3) Measure the voltage between A/T-ECU 

connector C-19 terminal No.2, No.3 and earth.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 14.

NO : 

Go to Step 12.

STEP 12. Connector check: C-19 A/T-ECU 
connector
Check for the contact with terminals.

Q: Is the check result normal?

YES : 

Go to Step 13.

NO : 

Repair the defective connector.

STEP 13. Check the harness between A/T control 
relay connector A-19X terminal No.3 and A/T-ECU 
connector C-19 terminal No.2, 3.
Check the power supply line for short or open circuit.

Q: Is the check result normal?

YES : 

Go to Step 7.

NO : 

Repair the wiring harness.

STEP 14. Connector check: C-20 A/T-ECU 
connector
Check for the contact with terminals.

Q: Is the check result normal?

YES : 

Go to Step 15.

NO : 

Repair the defective connector.

STEP 15. Check the harness between A/T control 
relay connector A-19X terminal No.2 and A/T-ECU 
connector C-20 terminal No.71.
Check the output line for short or open circuit.

Q: Is the check result normal?

YES : 

Go to Step 7.

NO : 

Repair the wiring harness.

TROUBLESHOOTING

AUTOMATIC TRANSMISSION

23A-73

Code No.P1790 Back up line system

AC510282

23

FUSIBLE
LINK

RELAY 
BOX

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

Back Up Line System Circuit

AB

AC509975AO

Harness side

A-115

Connector: A-115

AC510057

Harness side

A/T-ECU

C-12

AB

Connector: C-12

A/T-ECU

<RHD>

<LHD>

TROUBLESHOOTING

AUTOMATIC TRANSMISSION

23A-74

OPERATION
Always power is supplied to the ECU to prevent the 
reset of A/T-ECU memory when the ignition switch is 
turned to the LOCK (OFF) position.

DIAGNOSIS CODE SET CONDITION
If the battery voltage is 10 V or more and back-up 
voltage is less than 6 V while the ignition switch is 
ON position for 2 seconds or more, it is judged that 
there is a open circuit in the back-up line and diagno-
sis code No. P1790 is set.

PROBABLE CAUSES

• Damaged harness wires and connectors

• Malfunction of the A/T-ECU

DIAGNOSIS PROCEDURE

STEP 1. Measure the voltage at A/T-ECU 
connector C-12.
(1) Measure the voltage between A/T-ECU 

connector C-12 terminal No.38 and earth.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 4.

NO : 

Go to Step 2.

STEP 2. Connectors check: A-115 intermediate 
connector, C-12 A/T-ECU connector.
Check for the contact with terminals.

Q: Is the check result normal?

YES : 

Go to Step 3.

NO : 

Repair the defective connector.

STEP 3. Check the harness between A/T-ECU 
connector C-12 terminal No.38 and fusible link 
(23).
Check the power supply line for short or open circuit.

Q: Is the check result normal?

YES : 

Go to Step 5.

NO : 

Repair the wiring harness.

STEP 4. Connector check: C-12 A/T-ECU 
connector.
Check for the contact with terminals.

Q: Is the check result normal?

YES : 

Go to Step 5.

NO : 

Repair the defective connector.

STEP 5. Replace the A/T-ECU and then recheck 
the diagnosis code.
(1) Replace the A/T-ECU.
(2) Test drive the vehicle.
(3) Check the diagnosis code.

Q: Is the diagnosis code set?

YES : 

Go to Step 1.

NO : 

The inspection is complete.

Code No.P1901: CAN signal time-out (Engine-ECU)

CAUTION

• If diagnosis code P1901 is set in the A/T-ECU, 

always diagnose the CAN main bus line. If 
there is any fault in the CAN bus lines, an 
incorrect diagnosis code may be set.

• Whenever the ECU is replaced, ensure that 

the communication circuit is normal.

DIAGNOSIS CODE SET CONDITIONS

Current trouble

• Connector(s) or wiring harness in the CAN bus 

lines between the engine-ECU and the A/T-ECU, 
the power supply system to the engine-ECU, the 
engine-ECU itself, or the A/T-ECU may be defec-
tive.

Past trouble

• Carry out diagnosis with particular emphasis on 

connector(s) or wiring harness in the CAN bus 
lines between the engine-ECU and the A/T-ECU, 
and the power supply system to the engine-ECU. 
For diagnosis procedures, refer to "How to cope 
with past trouble" (Refer to GROUP 00, How to 
Use Troubleshooting/Inspection Service Points ).

NOTE: For a past trouble, you may not find it by the 

M.U.T.-III CAN bus diagnostics even if there is 
any failure in CAN bus lines. In this case, refer to 
GROUP 00, How to Use Troubleshooting/Inspec-
tion Service Points 

−

 How to Cope with Intermit-

tent Malfunctions ). and check the CAN bus lines.