Inspection Procedure J-2

Headlight, taillight: Headlights (low-beam) do not Illuminate.

Headlight Relay (Low) Drive Circuit:

Connectors:

CIRCUIT OPERATION
- If the headlight switch signal from the column switch turns on, the front-ECU makes the headlights illuminate. Whenever the headlights illuminate, the low-beam lights illuminate due to the headlight dimmer switch automatic resetting function.
- If the SWS communication line is defective, the low-beam headlights will illuminate by using other signal line (headlight back-up circuit).

TECHNICAL DESCRIPTION (COMMENT)
The headlight relay (low), column switch or the front- ECU may be defective.

NOTE: If only one of the headlights does not illuminate, the light bulb may be burned out or the harness wires between the light and the headlight relay (low) may be defective. In this case, check the circuit by referring to Headlight.

TROUBLESHOOTING HINTS
- Malfunction of the headlight relay (low)
- Malfunction of the column switch (turn-signal light and lighting switch)
- Malfunction of the front-ECU
- Damaged harness wires or connectors

DIAGNOSIS

Required Special Tools:
- MB991223: Test Harness Set
- MB991502: Scan Tool (MUT-II)
- MB991529: Diagnostic Trouble Code Check Harness

STEP 1. Check the DTC.

Q: Does the DTC set when the ignition switch is turned to the "LOCK" (OFF) position?

YES: Carry out the troubleshooting by referring to Diagnostic Trouble Code Chart.
NO: Go to Step 2 or 3 .

STEP 2. Check the input signal (by using scan tool MB991502).
Check the input signal from the headlight switch.

CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.

1. Connect scan tool MB991502 to the data link connector.
2. Check that the tone alarm of scan tool MB991502 sounds when the input signal enters.

Q: Does the tone alarm of scan tool MB991502 sound when the input signal enters?

YES: Go to Step 4.
NO: Check the headlight switch input circuit. Refer to Inspection Procedure O-15.

STEP 3. Check the input signal (by using a voltmeter).
Check the input signal from the headlight switch.

1. Use special tool MB991529 to connect a voltmeter between ground terminal 4 or 5 and ETACS-ECU terminal 9 of the data link connector.
2. Check that the voltmeter indicator deflects once when the input signal enters.

Q: Does the voltmeter indicator deflect?

YES: Go to Step 4.
NO: Check the headlight switch input circuit. Refer to Inspection Procedure O-15.

STEP 4. Check the headlight relay (low).

Q: Is the headlight relay (low) in good condition?

YES: Go to Step 5.
NO: Replace it. The headlights (low-beam) should illuminate normally.

STEP 5. Check the headlight relay (low) power supply circuit at the headlight relay (low) connector A-08X.
1. Disconnect the headlight relay (low) connector A-08X and measure at the relay box side.

2. Measure the voltages between terminal 3, 4 and ground.

Q: Are the voltages approximately 12 volts (battery positive voltage)?

YES: Go to Step 8.
NO: Go to Step 6.

STEP 6. Check headlight relay (low) connector A-08X for damage.

Q: Is headlight relay (low) connector A-08X in good condition?

YES: Go to Step 7.
NO: Repair or replace it. Refer to Harness Connector Inspection. The headlight (low-beam) should illuminate normally.

STEP 7. Check the harness wire between headlight relay (low) connector A-08X and battery.

Q: Is the harness wire between headlight relay (low) connector A-08X and battery in good condition?

YES: There is no action to be taken.
NO: Repair it. The headlights (low-beam) should illuminate normally.

STEP 8. Check headlight relay (low) connector A-08X and front-ECU connector A-09X for damage.

Q: Are headlight relay (low) connector A-08X and front ECU connector A-09X in good condition?

YES: Go to Step 9.
NO: Repair or replace them. Refer to Harness Connector Inspection. The headlights (low-beam) should illuminate normally.

STEP 9. Check the harness wire between headlight relay (low) connector A-08X and front-ECU connector A-09X.

Q: Is the harness wire between headlight relay (low) connector A-08X and front-ECU connector A-09X in good condition?

YES: Go to Step 10.
NO: Repair it. The headlights (low-beam) should illuminate normally.

STEP 10. Check headlight connectors A-24 and A-34 for damage.

Q: Are headlight connectors A-24 and A-34 in good condition?

YES: Go to Step 11.
NO: Repair or replace it. Refer to Harness Connector Inspection. The headlights (lowbeam) should illuminate normally.

STEP 11. Check the harness wires between headlight relay (low) connector A-08X and headlight connectors A-24 and A-34.

NOTE: After checking intermediate connector C-05, check the wires. If intermediate connector C-05 is damaged, repair or replace it. Refer to Harness Connector Inspection.

Q: Are the harness wires between headlight relay (low) connector A-08X and headlight connectors A-24 and A-34 in good condition?

YES: Replace the front-ECU. The headlights (low-beam) should illuminate normally.
NO: Repair them. The headlights (low-beam) should illuminate normally.