Daytime running lights (DRL) without HID RPO TT4

The daytime running lights use the same lamps as the parking light. One filament is for the daytime running lights and one is for the parking light. DRL is activated if the following conditions are met:

1. The engine is running.
2. The headlamp switch is in the AUTOMATIC LIGHT position.
3. Main beam and dipped beam are switched off.

If the headlamp switch is turned to the OFF position, automatic lighting and DRL are deactivated.

The ambient light sensor monitors the light conditions outside the car. The ambient light sensor transmits a voltage signal that varies between 0.2 and 4.9 V depending on the light conditions outside the car. The HVAC control module sends a low reference ground and 5 V reference signals to the ambient light sensor. BCM monitors the signal circuit for the ambient light sensor to determine whether the light conditions are suitable for daytime running lights or dipped beam when the headlamp switch is in the AUTOMATIC LIGHT position. In daylight conditions, BCM orders daytime running lights ON by grounding the left and right daytime running lights relay via separate relay circuits for the left and right daytime running lights. When BCM grounds the relay circuits, the relay coils for left and right daytime running lights are energized and both relay contacts close. With both relay contacts closed, battery voltage is supplied to the left and right daytime running light lamps. All functions or conditions that activate the headlamps deactivate the daytime running light function.