Inspection Procedure 10: The auto lamp function does not work normally. <Vehicles with LDW>

  • Before replacing the ECU, ensure that the power supply circuit, the earth circuit and the communication circuit are normal.
  • When the ETACS-ECU of vehicles without KOS is replaced, the encrypted code of the ignition key needs to be registered to the ETACS-ECU. (If the encrypted code is not registered, the engine cannot be started. Register the encrypted code as described in Immobilizer System - How to Register Key ID .)


The ETACS-ECU operates this function in accordance with the input signals from driving distance, LDW-ECU (light sensor), and column switch (auto lamp switch). Also, when the column switch (lighting switch) is in the "AUTO" position, and when an abnormality is present to the auto lamp circuit, the fail-safe function is activated and the low beam is turned ON at all times regardless of the brightness around the vehicle.


If the auto lamp function does not work normally, the above input signal circuit(s) or the ETACS-ECU may have a problem.



STEP 1. M.U.T.-III CAN bus diagnostics

Use the M.U.T.-III to diagnose the CAN bus lines.

Q. Is the check result normal?

Go to Step 2.

Repair the CAN bus line (Refer to GROUP 54C - Troubleshooting ).

STEP 2. M.U.T.-III other system diagnosis code

Check if diagnosis code is set to the ETACS-ECU.

Q. Is the diagnosis code set?

Troubleshoot the ETACS-ECU (Refer to ).

Go to Step 3.

STEP 3. Check that the headlamps operate.

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

Q. Is the check result normal?

Go to Step 4.

Refer to Inspection Procedure 1 "None of the low-beam headlamps illuminate." .

STEP 4. M.U.T.-III data list

Use the ETACS-ECU service data to check the signals related to the operation of auto lamp function.

Item No.
Item name
Normal condition
Item 348
Headlamp switch (auto)
OK: Normal condition is displayed.

Q. Is the check result normal?

Go to Step 5.

Troubleshoot the ETACS-ECU. Refer to Inspection Procedure 11 "The column switch signal is not received" .

STEP 5. LDW-ECU (light sensor) check

Check the LDW-ECU (light sensor). Refer to .

Q. Is the check result normal?

Go to Step 6.

Replace the LDW-ECU.

STEP 6. Retest the system

Check that the auto lamp function works normally.

Q. 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.