Inspection Procedure 3: The headlights (low-beam) illuminate regardless of the lighting switch positions. (High-beam does not illuminate): Diagnosis

Required Special Tools: 

• MB992006: Extra fine probe
• MB991223: Harness set

1. STEP 1. Using scan tool (M.U.T.-III), diagnose the CAN bus line 
   CAUTION: To prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
   1. Connect scan tool (M.U.T.-III). Refer to "HOW TO CONNECT THE SCAN TOOL (M.U.T.-III) ."
   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 (Refer to DIAGNOSIS ).
2. STEP 2. Using scan tool (M.U.T.-III), read the ETACS diagnostic trouble code 

   Check if DTC is stored in the ETACS-ECU.

   Q: Is the DTC stored? 

   • YES:  Troubleshoot the ETACS-ECU. Refer to DIAGNOSTIC TROUBLE CODE CHART .
   • NO:  Go to Step 3.
3. STEP 3. Using scan tool (M.U.T.-III), read the ASC diagnostic trouble code. 

   Check if DTC is stored in the ASC.

   Q: Is the DTC stored? 

   • YES:  Troubleshoot the ASC. Refer to DIAGNOSTIC TROUBLE CODE CHART .
   • NO < Vehicles with lighting control sensor >:  Go to Step 4.
   • NO < Vehicles with LDW >:  Go to  Step 5.
4. STEP 4. Using scan tool (M.U.T.-III), read the LIN diagnostic trouble code 

   Check if DTC is stored in the LIN.

   Q: Is the DTC stored? 

   • YES:  Refer to DTC CHART .
   • NO:  Go to  Step 6.
5. STEP 5. Using scan tool (M.U.T.-III), read the LDW diagnostic trouble code 

   Check if DTC is stored in the LDW.

   Q: Is the DTC stored? 

   • YES:  Refer to DTC CHART .
   • NO:  Go to Step 6.
6. STEP 6. Using scan tool (M.U.T.-III), 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 name	Normal condition
     Item 348	Head light switch (auto)	ON

     OK: Normal condition is displayed. 

   Q: Is the check result normal? 

   • YES < Vehicles without auto light function >:  Go to  Step 8.
   • YES < Vehicles with auto light function >:  Go to Step 7.
   • NO:  Troubleshoot the ETACS-ECU. Refer to INSPECTION PROCEDURE 11: THE COLUMN SWITCH SIGNAL IS NOT RECEIVED .
7. STEP 7. Lighting control sensor < Vehicles with lighting control sensor > or LDW-ECU (light sensor) < Vehicles with LDW > check 

   Check the lighting control sensor < Vehicles with lighting control sensor > (Refer to LIGHTING CONTROL SENSOR (LIGHT SENSOR) CHECK < VEHICLES WITH LIGHTING CONTROL SENSOR >  ) or LDW-ECU (light sensor) < Vehicles with LDW > (Refer to LDW-ECU (LIGHT SENSOR) CHECK < Vehicles with LDW) >  ).

   Q: Is the check result normal? 

   • YES:  Go to Step 8.
   • NO:  Replace the lighting control sensor < Vehicles with lighting control sensor > or LDW-ECU (light sensor) < Vehicles with LDW >.
8. STEP 8. Retest the system 

   Check that the headlights illuminate normally.

   Q: Is the check result normal? 

   • YES:  The trouble can be an intermittent malfunction (Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTION ).
   • NO:  Replace the ETACS-ECU.