Inspection Procedure 10
Inspection Procedure 10: The auto light function does not work normally.
CAUTION:
Whenever the ECU is replaced, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.
OPERATION
The ETACS-ECU operates this function in accordance with the input signals from driving distance, lighting control sensor, and column switch (auto light switch). Also, when the column switch (lighting switch) is in the "AUTO" position, and when an abnormality is present to the auto light circuit, the fail-safe function is activated and the low beam is turned ON at all times regardless of the brightness around the vehicle.
TECHNICAL DESCRIPTION (COMMENT)
If the auto light function does not work normally, the above input signal circuit(s) or the ETACS-ECU may have a problem.
TROUBLESHOOTING HINTS
- Malfunction of the lighting control sensor
- Malfunction of the column switch
- Malfunction of the ETACS-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. Using scan tool MB991958, diagnose the CAN bus line
(1)
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 scan tool MB991958. Refer to "How to connect the Scan Tool (M.U.T.-III) Reading and Clearing Diagnostic Trouble Codes."
(2)Turn the ignition switch to the "ON" position.
(3)Diagnose the CAN bus line.
(4)Turn the ignition switch to the "LOCK" (OFF) position.
Q. Is the CAN bus line found to be normal?
YES Go to Step 2.
NO Repair the CAN bus line CAN Bus Diagnostics Chart).
STEP 2. Using scan tool MB991958, read the diagnostic trouble code.
Check if DTC is set to the LIN.
Q. Is the DTC set?
YES Refer to DTC chart Headlight.
NO Go to Step 3.
STEP 3. Using scan tool MB991958, read the ETACS diagnostic trouble code.
Check if DTC is set to the ETACS-ECU.
Q. Is the DTC set?
YES Troubleshoot the ETACS (Refer to Electronic Time and Alarm Control System (ETACS)).
NO Go to Step 4.
STEP 4. Check that the headlights operate.
Check that the headlights (low-beam) illuminate normally.
Q. Is the check result normal?
YES Go to Step 5.
NO Refer to Inspection Procedure 1 "None of headlights (low-beam) illuminates." Inspection Procedure 1.
STEP 5. Using scan tool MB991958, check data list
Use the ETACS-ECU service data to check the signals related to the operation of auto light function.
- Turn the lighting switch to the "AUTO" position.
Q. Does scan tool MB991958 display the items "Headlight switch (auto)" as normal condition?
YES Go to Step 6.
NO Troubleshoot the ETACS-ECU. Refer to ETACS, Diagnosis Symptom Chart.
STEP 6. Lighting control sensor check
Check the lighting control sensor. Refer to Lighting Control Sensor Check.
Q. Is the check result normal?
YES Go to Step 7.
NO Replace the lighting control sensor.
STEP 7. Retest the system
Check that the auto light function works normally.
Q. Is the check result normal?
YES The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Replace the ETACS-ECU.