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Inspection Procedure 3: The headlights (low-beam) illuminate regardless of the lighting switch positions. (High-beam does not illuminate)
 
 
cautionBefore 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
  • 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 off the power supply mode of the electric motor switch 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) Press the electric motor switch to turn on the power supply mode.
(3) Diagnose the CAN bus line.
(4) Press the electric motor switch to turn off the power supply mode.
Is the CAN bus line found to be normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C - Diagnosis ).
 
STEP 2. Using scan tool (M.U.T.-IIISE), read the ETACS 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 ASC 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 LIN DTC.
Check if DTC is set in the LIN.
Is the DTC set?
Refer to DTC chart .
Go to Step 5.
 
STEP 5. Using scan tool (M.U.T.-IIISE), 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.
 
Item No.Item nameNormal condition
Item 348Head light 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 10 "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.