Inspection Procedure 1

Inspection Procedure 1: None of headlights (low-beam) illuminates.

CAUTION: Whenever the ECU is replaced, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.

Headlight Relay (Low-Beam) Circuit:

TECHNICAL DESCRIPTION (COMMENT)
If none of headlights (low-beam) illuminates, the headlight switch input circuit, headlight relay (LOW), or ETACS-ECU may have a problem.

TROUBLESHOOTING HINTS
- Malfunction of column switch
- Malfunction of headlight relay (LOW)
- Malfunction of the ETACS-ECU
- Damaged harness wires and connectors

DIAGNOSIS

Required Special Tools:
- MB992006: Extra fine probe
- MB991223: Harness set
- 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. Using scan tool MB991958, read the diagnostic trouble code.

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 too (M.U.T.-III)." How to Connect the Scan Tool (M.U.T.-III)
2. Turn the ignition switch to the "ON" position.
3. Check whether the ETACS-ECU related DTC is set.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the DTC set?

YES : Diagnose the ETACS-ECU. Diagnostic Trouble Code Descriptions

NO : Go to Step 2.

STEP 2. Using scan tool MB991958, check data list

Use the ETACS-ECU service data to check the signals related to the operation of headlight function.
- Turn the headlight switch to the ON position.







Q: Do scan tool MB991958 display the items "Headlight switch" as normal condition?

YES : Go to Step 3.

NO : Troubleshoot the ETACS-ECU. Trouble Symptom Chart For Input Signal

STEP 3. Check headlight relay (LOW) connector A-25X for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is headlight relay (LOW) connector A-25X in good condition?

YES : Go to Step 4.

NO : Repair the damaged parts.

STEP 4. Check the battery power supply circuit to the headlight relay (LOW). Measure the voltage at headlight relay (LOW) connector A-25X.

CAUTION: The top and bottom of the headlight relay (LOW) are difficult to identify. Prior to inspection, confirm the triangle mark on the relay box.

1. Disconnect headlight relay (LOW) connector A-25X and measure the voltage available at the relay box side of the connector.
2. Measure the voltage between terminal 4 and ground.

OK: The voltage should measure approximately 12 volts (battery positive voltage).

Q: Is the measured voltage approximately 12 volts (battery positive voltage)?

YES : Go to Step 5.

NO : Go to Step 7.

STEP 5. Check ETACS-ECU connector C-312 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is ETACS-ECU connector C-312 in good condition?

YES : Go to Step 6.

NO : Repair the damaged parts.

STEP 6. Check the wiring harness between headlight relay (LOW) connector A-25X (terminal 1) and ETACS-ECU connector C-312 (terminal 6).

- Check the output line for open circuit.

Q: Is the wiring harness between headlight relay (LOW) connector A-25X (terminal 1) and ETACS-ECU connector C-312 (terminal 6) in good condition?

YES : Go to Step 8.

NO : The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary. Verify that the low-beam headlights illuminate normally.

STEP 7. Check the wiring harness between headlight relay (LOW) connector A-25X (terminal 4) and the fusible link (36).

- Check the power supply line for open circuit.

Q: Is the wiring harness between headlight relay (LOW) connector A-25X (terminal 4) and fusible link (36) in good condition?

YES : Go to Step 8.

NO : The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary. Verify that the low-beam headlights illuminate normally.

STEP 8. Temporarily replace the headlight relay (LOW), and retest the system.

Temporarily replace the headlight relay (LOW), check that the headlights (low-beam) illuminate normally.

Q: Does the headlights (low-beam) do not illuminate in good condition?

YES : Replace the headlight relay (LOW).

NO : Replace the ETACS-ECU.