What causes the Cadillac ATSL daytime running lights not to work?

[EliLynn]

Possible reasons for the Cadillac ATSL daytime running lights not working include the daytime running lights being turned off, a blown fuse for the daytime running lights, wiring harness failure, guide ring driver failure, or issues with the daytime running light bulbs. Below are detailed explanations and solutions: Daytime running lights turned off: The daytime running lights may be disabled in the vehicle settings. Simply enable them in the settings. Blown fuse for the daytime running lights: If both left and right lights are not working, replace the fuse. Wiring harness failure: Park the vehicle and inspect the wiring harness between the headlight control module and the daytime running lights. If the issue persists, visit a professional repair shop. Guide ring driver failure: For example, the driver connector may be loose or poorly connected. Secure the driver connector properly. Daytime running light bulb issue: If the bulb filament has quality issues, its resistance may increase with temperature, causing the working current to decrease and the daytime running light to turn off. Replace the bulb.