Inspection Procedure J-2

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

Headlight Relay (Low-Beam) Circuit Part 1:

Headlight Relay (Low-Beam) Circuit Part 2:

NOTE: This troubleshooting procedure requires the use of scan tool MB991958 and SWS monitor kit MB991813. For details on how to use the SWS monitor, refer to "How to use SWS monitor." 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
- The column switch (turn-signal light and lighting switch) may be defective
- The front-ECU may be defective
- The wiring harness or connectors may have loose, corroded, or damaged terminals, or terminals pushed back in the connector

DIAGNOSIS

Required Special Tools:
- MB991223: Harness Set
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: Vehicles communication interface (V.C.I.)
- MB991827: MUT-III USB cable
- MB991911: MUT-III Main harness B
- MB991813: SWS monitor kit
- MB991806: SWS monitor cartridge
- MB991812: SWS monitor harness (for column-ECU)
- MB991922: Probe harness

STEP 1. Use scan tool MB991958 to select "ECU COMM CHK" on the SWS monitor display.
Check the following ECUs:
- Column-ECU
- Front-ECU

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. Connect special tool MB991910 before connecting special tool MB991812. Be sure to connect special tool MB991806 after turning on special tool MB991824.







1. Connect the special tool. Refer to "How to connect SWS monitor." How to Connect SWS Monitor
2. Turn the ignition switch to the "LOCK" (OFF) position.
3. Operate scan tool MB991958 according to the procedure below to display "ECU COMM Check."
a. Select "Interactive Diagnosis."
b. Select "System select."
c. Select "SWS."
d. Select "SWS MONITOR."
e. Select "ECU COMM Check."

4. Scan tool MB991958 should show "OK" on the "ECU COMM Check" menus for both the "COLUMN ECU" and the "FRONT ECU" menus.

Q: Are "OK" displayed on the "COLUMN ECU" and "FRONT ECU" menu?

"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 not possible."
"NG" is displayed on the "FRONT ECU" menu: Refer to Inspection procedure A-4 "Communication with front-ECU is not possible."

STEP 2. Check the input signal by using "FUNCTION DIAG." menu of the SWS monitor.
Check the input signals from the following switches:
- Ignition switch: ON
- Lighting switch: HEAD







1. Operate scan tool MB991958 according to the procedure below to display "HEADLIGHT LO."
a. Select "Interactive Diagnosis."
b. Select "System select."
c. Select "SWS."
d. Select "SWS MONITOR."
e. Select "Function Diag."
f. Select "LIGHTING."
g. Select "HEADLIGHT LO."




2. Check that normal conditions are displayed for the items described in the table.

Q: Does the scan tool MB991958 display the items "HEADLIGHT SW", "H/L AUTO-CUT" and "FRONT ECU ACK" as normal condition?

Normal conditions are displayed for all the items: Go to Step 3.
Normal condition is not displayed for "HEADLIGHT SW": Normal condition is not displayed on the "HEADLIGHT SW": Refer to Inspection Procedure O-7 "ETACS-ECU does not receive a signal from the headlight switch."
Normal condition is not displayed for "H/L AUTO-CUT": Normal condition is not displayed on the "H/L AUTO-CUT": Refer to Inspection Procedure J-9 "Headlight automatic shutdown function does not work normally."
Normal condition is not displayed for "FRONT ECU ACK": Normal condition is not displayed on the "FRONT ECU ACK": Replace the ECU. Check that the headlights (low-beam) illuminate normally.




STEP 3. Check the front-ECU connector A-10X for loose, corroded or damaged terminals, or terminals pushed back in the connector.

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

YES: Go to Step 4.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. Verify that the headlights (low-beam) illuminate normally.

STEP 4. Check the battery power supply circuit to the front-ECU. Measure the voltage at front-ECU connector A-10X.




1. Disconnect front-ECU connector A-10X and measure the voltage available at the relay box side of the connector.




2. Measure the voltage between terminal 3 and ground.
- The voltage should equal approximately 12 volts (battery positive voltage).

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

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

NO: Go to Step 5.




STEP 5. Check the wiring harness between front-ECU connector A-10X (terminal 3) and the battery.

Q: Is the wiring harness between front-ECU connector A-10X (terminal 3) and the battery in good condition?

YES: No action is necessary and testing is complete.

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. Check that the headlights (low-beam) illuminate normally.