Discharge Headlight System


Light control ECU (ECU for discharge headlight)
The light control ECU is an electronic control unit required to turn on the discharge headlight bulbs. It is located beneath the right and left discharge headlights. It performs optimal control of the current supplied to the bulbs in order to ensure rapid, optimum light intensity when the bulbs emit light and stable, continuous lighting. It is equipped with a fail-safe function to prevent high voltage.
The output terminal of the light control ECU generates extremely dangerous high voltage, so handle with great care. To prevent risk of danger, caution labels are positioned on the side of the headlights and the light control ECU itself.
The glass part and electrodes of discharge headlight bulbs generate dangerously high voltage (approx. 20,000 V). Do not touch them.
Turn the lights on only after the bulbs are completely installed. Do not use any power source other than the vehicle’s.
When replacing the bulbs, be sure to follow the procedure in the Repair Manual.
Fail-safe function
The light control ECU judges that a malfunction has occurred and activates a fail-safe function under any of the following conditions.
(1)An input malfunction is detected
If input voltage is outside the operating voltage (9-16 V), the fail-safe function will turn off the discharge headlights. If this happens, the discharge headlights will come on again as soon as the operating voltage resumes.
(2)An output malfunction is detected (open/short)/light flashing is detected
If there is a malfunction in output voltage or if the discharge headlights are flashing, the fail-safe function will turn off the discharge headlights. If this happens, the ECU cannot determine whether the cause is the output malfunction. After checking for malfunctions in the fuse and wire harness systems, replace the discharge headlight bulb. If the problem is not solved, replace the light control ECU.
(3)A bulb open is detected
If there is no discharge headlight bulb in the headlight bulb socket, a bulb open is detected. The fail-safe function will stop the generation of high voltage. If this happens, turn the ignition switch off and install a bulb. This will release the fail-safe function.

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