GMC Repair: Daytime Running lights, ambient light sensor, daytime running lights

Question
Hello there and thankyou in advance. I have a 2001 Yukon and when I start my truck instead of just the DRL coming on all the lights come on like I'm driving at night, headlights, tail lights and no DRL. Any idea what I could or should be looking for?  Thanks again

Answer
Hi
first there is an ambient light sensor located in the middle of the dash between the defrost vents close to the windshield.
If it is fallen into dash or if it is faulty, it could trick the automatic lamps into thinking it is dark outside.
I would go have your local repair shop scan for BCM codes and see if there is a clue there.
The only other devise in this system besides the BCM, Ambient light sensor,  is the headlamp switch.
Scanning BCM MAY reveal trouble codes which can then be diagnosed.
Just advise from experience.
Hope it helps
Good Luck
PAul