DTC 31

Code No.31 Leveling Unit Abnormality

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

Headlight Leveling Unit Circuit (Part 1):

Headlight Leveling Unit Circuit (Part 2):

TROUBLE JUDGMENT
If the headlight leveling unit signal line is short-circuited, DTC 31 is set.

TECHNICAL DESCRIPTION (COMMENT)
The wiring harness and connector(s) between the headlight leveling unit and the headlight automatic leveling-ECU, headlight assembly (headlight leveling unit), or headlight automatic leveling-ECU may have a problem.

TROUBLESHOOTING HINTS
- Malfunction of headlight assembly (headlight leveling unit)
- Malfunction of the headlight automatic leveling-ECU
- The wiring harness or connectors may have loose, corroded, or damaged terminals, or terminals pushed back in the connector

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)

STEP 1. Check headlight leveling unit (LH) connector A-37,headlight automatic leveling-ECU connector C-110 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is headlight leveling unit (LH) connector A-37,headlight automatic leveling-ECU connector C-110?

YES : Go to Step 2.

NO : Repair the damaged parts.

STEP 2. Check the wiring harness between headlight leveling unit (LH) connector A-37 (terminal No. 10) and headlight automatic leveling-ECU connector C-110 (terminal No. 3)

Q: Is wiring harness between headlight leveling unit (LH) connector A-37 (terminal No. 10) and headlight automatic leveling-ECU connector C-110 (terminal No. 3) in good condition?

YES : Go to Step 3.

NO : Repair the wiring harness.

STEP 3. Using scan tool MB991958, Check whether the diagnostic trouble code is reset.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.




1. Connect scan tool MB991958. Refer to "How to connect scan tool." Scan Tool Connecting
2. Turn the ignition switch to the "ON" position.
3. Erase the DTC.
4. Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
5. Check if DTC is set.

Q: Is DTC 31 set?

YES : Go to Step 4.

NO : The trouble, such as a poor connector connection from the headlight leveling unit (LH) to headlight automatic leveling-ECU or an open circuit of wiring harness, can be an intermittent malfunction. (Refer to general (body and chassis) - How to use Troubleshooting/inspection Service Points - How to cope with Intermittent Malfunction.)

STEP 4. Check headlight leveling unit (RH) connector A-56,headlight automatic leveling-ECU connector C-110 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is headlight leveling unit (RH) connector A-56,headlight automatic leveling-ECU connector C-110 in good condition?

YES : Go to Step 5.

NO : Repair the defective connector.

STEP 5. Check the wiring harness between headlight leveling unit (RH) connector A-56 (terminal No. 10) and headlight automatic leveling-ECU connector C-110 (terminal No. 12).

Q: Is wiring harness between headlight leveling unit (RH) connector A-56 (terminal No. 10) and headlight automatic leveling-ECU connector C-110 (terminal No. 12) in good condition?

YES : Go to Step 6.

NO : Repair the wiring harness.

STEP 6. Using scan tool MB991958, Check whether the diagnostic trouble code is reset.

1. Turn the ignition switch to the "ON" position.
2. Erase the DTC.
3. Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
4. Check if DTC is set.

Q: Is DTC 31 set?

YES : Go to Step 7.

NO : The trouble, such as a poor connector connection from the headlight leveling unit to headlight automatic leveling-ECU or an open circuit of wiring harness, can be an intermittent malfunction. (Refer to general (body and chassis) - How to use Troubleshooting/inspection Service Points - How to Cope with Intermittent Malfunction.)

STEP 7. Using scan tool MB991958, Check whether the diagnostic trouble code is reset.

Replace the headlight assembly (LH), and then check again if DTC 31 is set.

1. Turn the ignition switch to the "ON" position.
2. Erase the DTC.
3. Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
4. Check if DTC is set.

Q: Is DTC 31 set?

YES : Go to Step 8.

NO : The procedure is complete.

STEP 8. Using scan tool MB991958, Check whether the diagnostic trouble code is reset.

Replace the headlight assembly (RH), and then check again if DTC 31 is set.

1. Turn the ignition switch to the "ON" position.
2. Erase the DTC.
3. Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
4. Check if DTC is set.

Q: Is DTC 31 set?

YES : Replace the headlight automatic leveling-ECU.

NO : The procedure is complete.