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Inspection Procedure 2: The headlights (low-beam) illuminate regardless of the lighting switch positions. (High-beam does not illuminate)
 
 
caution
  • Before replacing the ECU, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.
 
 
 
 
TECHNICAL DESCRIPTION (COMMENT)
If the headlights illuminate only at low-beam regardless of the lighting switch position, the headlight fail-safe function may be active.
 
 
TROUBLESHOOTING HINTS
  • The column switch may be defective
  • The lighting control sensor may be defective <Vehicles with lighting control sensor>
  • The ETACS-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:
  • MB992006: Extra fine probe
  • MB991223: Harness set
STEP 1. Using scan tool (M.U.T.-IIISE), diagnose the CAN bus line.
(1)
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-IIISE).
Connect scan tool (M.U.T.-IIISE). Refer to "How to connect the Scan Tool (M.U.T.-IIISE) ."
(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.
Is the CAN bus line found to be normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C - Troubleshooting ).
 
STEP 2. Using scan tool (M.U.T.-IIISE), read the DTC.
Check if DTC is set in the ETACS-ECU.
Is the DTC set?
Troubleshoot the ETACS-ECU. Refer to .
Go to Step 3.
 
STEP 3. Using scan tool (M.U.T.-IIISE), read the other system DTC.
Check if DTC is set in the ASC.
Is the DTC set?
: Troubleshoot the ASC. Refer to .
Go to Step 4.
 
STEP 4. Using scan tool (M.U.T.-IIISE), read the other system DTC.
Check if DTC is set in the LIN.
Is the DTC set?
Refer to DTC chart .
: Go to Step 5.
: Go to Step 7.
 
STEP 5. Using scan tool (M.U.T.-IIISE), check data list.
Use the ETACS-ECU data list to check the signals related to the operation of auto light function.
  • Turn the lighting switch to the "AUTO" position.
 
Item No.Item nameNormal condition
22Headlight switch (Auto)ON
OK: Normal condition is displayed.
Is the check result normal?
Go to Step 6.
: Troubleshoot the ETACS-ECU. Refer to Inspection Procedure 11 "The column switch signal is not received" .
 
STEP 6. Lighting control sensor check.
Check the lighting control sensor (Refer to ).
Is the check result normal?
Go to Step 7.
Replace the lighting control sensor.
 
STEP 7. Retest the system.
Check that the headlights illuminate normally.
Is the check result normal?
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to use Troubleshooting/inspection Service Points - How to Cope with Intermittent Malfunction ).
Replace the ETACS-ECU.