Daytime Running Lamps (DRL) without HID RPO T4F/T95

WARNING: This page is about a different car, the 2019 Buick Cascada, 2018 Buick Cascada, and 2017 Buick Cascada. However, it is still accessible from the selected car via links, so may be relevant.

The DRL bulbs are combined with the park lamps. One filament is for the DRL and one for the park lamps. The DRL will operate when the following conditions are met:

Engine is running.
Headlamp switch in AUTOMATIC LIGHT position.
The high and low beam headlamps are OFF.

By turning the headlamp switch in the OFF position the automatic light function and the DRL will be deactivated.

The rain/ambient light sensor module is used to monitor outside lighting conditions. The rain/ambient light sensor module provides a serial data message to the body control module (BCM) based on outside lighting conditions to determine if outside lighting conditions are correct for either daytime running lights or automatic lamp control when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRL ON by applying ground to the left and right daytime running light relays via separate left and right daytime running light relay control circuits. When the BCM applies ground to the relay control circuits, the left and right daytime running light relay coils energize causing both relay switch contacts to close. With the left and right daytime running lights relay switch contacts closed, battery voltage flows to the left and right daytime running lights. Any function or condition that turns on the headlamps will cancel daytime running lights operation.