Code No.31 Malfunction of the Levelling Unit

caution

Before replacing the ECU, ensure that the communication circuit is normal.

TROUBLE JUDGMENT

If the headlamp levelling unit signal line is short-circuited, diagnosis code No. 31 is set.

COMMENTS ON TROUBLE SYMPTOM

The wiring harness and connector(s) between the headlamp levelling unit and the headlamp automatic levelling ECU, headlamp assembly (headlamp levelling unit), or headlamp automatic levelling ECU may have a problem.

PROBABLE CAUSES

Malfunction of headlamp assembly (headlamp levelling unit)
Malfunction of the headlamp automatic levelling ECU
Damaged harness wires and connectors

DIAGNOSIS PROCEDURE

STEP 1. Connector check: A-37 headlamp levelling unit (LH) connector, C-112 headlamp automatic levelling ECU connector

Q. Is the check result normal?

Go to Step 2.

Repair the defective connector.

STEP 2. Wiring harness check between the A-37 headlamp levelling unit (LH) connector terminal No. 10 and the C-112 headlamp automatic levelling ECU connector terminal No. 3

Check the signal lines for open circuit and short circuit.

Q. Is the check result normal?

Go to Step 3.

Repair the wiring harness.

STEP 3. Check whether the diagnosis code is reset.

Q. Is diagnosis code No. 31 set?

Go to Step 4.

The trouble, such as a poor connector connection from the headlamp levelling unit (LH) to headlamp automatic levelling ECU or an open circuit of wiring harness, can be an intermittent malfunction (Refer to GROUP 00 - How to use Troubleshooting/inspection Service Points - How to cope with Intermittent Malfunction

STEP 4. Connector check: A-54 headlamp levelling unit (RH) connector

Q. Is the check result normal?

Go to Step 5.

Repair the defective connector.

STEP 5. Wiring harness check between the A-54 headlamp levelling unit (RH) connector terminal No. 10 and the C-112 headlamp automatic levelling ECU connector terminal No. 12

Check the signal lines for open circuit and short circuit.

Q. Is the check result normal?

Go to Step 6.

Repair the wiring harness.

STEP 6. Check whether the diagnosis code is reset.

Q. Is diagnosis code No. 31 set?

Go to Step 7.

The trouble, such as a poor connector connection from the headlamp levelling unit to headlamp automatic levelling ECU or an open circuit of wiring harness, can be an intermittent malfunction (Refer to GROUP 00 - How to use Troubleshooting/inspection Service Points - How to cope with Intermittent Malfunction

STEP 7. Check whether the diagnosis code is reset.

Replace the headlamp assembly (LH), and then check again if the diagnosis code No.31 is set.

Q. Is diagnosis code No. 31 set?

Go to Step 8.

The diagnosis is complete.

STEP 8. Check whether the diagnosis code is reset.

Replace the headlamp assembly (RH), and then check again if the diagnosis code No.31 is set.

Q. Is diagnosis code No. 31 set?

Replace the headlamp automatic levelling ECU.

The diagnosis is complete.