Inspection Procedure I-2

Headlight, Tail Light: Headlights (Low-beam) do not Illuminate Normally

Headlight Relay (Low-beam) Circuit:

NOTE: This troubleshooting requires use of scan tool MB991502 and SWS monitor kit MB991862. For details of how to use the SWS monitor, refer to "How to use SWS monitor".

CIRCUIT OPERATION
- When the lighting switch is set to "HEAD" position, the "HEAD" signal is sent through the column-ECU (incorporated in the column switch) to the front-ECU. IF the front-ECU receives the "HEAD" signal through the column-ECU, the front-ECU turns on the headlight relay (incorporated in the front-ECU), thus causing the headlights to illuminate. The headlights always illuminate at low-beam by the headlight dimmer switch automatic resetting function.
- If the SWS communication line is defective, the front-ECU operates the headlights by using the other communication lines (headlight backup circuit) instead of that line.

TECHNICAL DESCRIPTION (COMMENT)
If the headlights (low-beam) do not illuminate normally, the column switch or the front-ECU may be defective.

TROUBLESHOOTING HINTS
- Malfunction of 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)
- MB991862: SWS monitor kit

STEP 1. Use scan tool to select "ECU CHECK" on the SWS monitor display.
Check the following ECUs:
- column-ECU
- front-ECU

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. Also connect SWS monitor kit MB991862 after turning on scan tool MB991502.







1. Connect scan tool MB991502 to the data link connector.
2. Connect SWS monitor kit MB991862 to the column switch connector.
3. When the ignition switch is turned to the "LOCK" (OFF) position, scan tool MB991502 should show "OK" on the "ECU CHECK" menu.

Q: Are "OK" displayed on the "COLUMN ECU" and "FRONT ECU"?
"OK" are displayed for all the items : Go to Step 2.
"NG" is displayed on the "COLUMN ECU" menu : Refer to Inspection Procedure A-2 "Communication with column switch (column-ECU) is impossible."
"NG" is displayed on the "FRONT ECU" menu : Refer to Inspection procedure A-4 "Communication with front-ECU is impossible"










STEP 2. Check the input signal by using service data of the SWS monitor.
Check the input signals from the following switches:
- ignition switch: ON
- lighting switch: HEAD

Select "LIGHTING - HEADLIGHT LO" (FUNCTION DIAG), and check that normal conditions are displayed on the items described in the table.

Q: Are normal conditions displayed on the "HEADLIGHT SW", "H/L AUTO-CUT" and "FRONT ECU ACK"?

YES: Go to Step 3.

NO:
- Normal condition is not displayed on the "HEADLIGHT SW: Refer to Inspection Procedure L-5 "ETACS-ECU does not receive a signal from the headlight switch."
- Normal condition is not displayed on the "H/L AUTO-CUT": Refer to Inspection Procedure I-8 "Headlight automatic shutdown function does not work normally."
- Normal condition is not displayed on the "FRONT ECU ACK": Replace the front-ECU. Check that the headlights (low-beam) illuminate normally.




STEP 3. Measure at front-ECU connector A-10X in order to check the battery circuit of power supply system to the front-ECU.
1. Disconnect front-ECU connector A-10X, and measure at the relay box side.
2. Measure the voltage between terminal 3 and ground.
- The measured value should be approximately 12 volts (battery positive voltage).

Q: Does the measured voltage correspond with this range?

YES: Replace the front-ECU. Check that the headlights (low-beam) illuminate normally.

NO: Go to Step 4.




STEP 4. Check the front-ECU connector A-10X for damage.

Q: Is the front-ECU connector A-10X in good condition?

YES: Go to Step 5.

NO: Repair or replace the connector. Refer to Harness Connector Inspection. Check that the headlights (low-beam) illuminate normally.




STEP 5. Check the wiring harness between front-ECU connector A-10X and the battery.

Q: Is the wiring harness between front-ECU connector A-10X and the battery in good condition?

YES: No action to be taken.

NO: Repair the wiring harness. Check that the headlights (low-beam) illuminate normally.