GM-TECH, Lights Out!

millerwd · January 25, 2005

On my way to work this morning, 05:00 , suddenly the lights shut off!

Fornuately I had the wimpa$$ fog lamps on so I could see the shoulder. I turned the light swithch all the way counter clockwise and then all the way clockwise and they come back on. When I turned the switch to Auto they stayed on.

Failure analysis. possibilties: bad photo optic sensor, bad relay, bad switch

I do have my fogs. low and highs dioded together, so there is the possibility that could be a factor.

I am not aware of a circiut breaker in the light circuit that may have tripped.

It was foggy and I had my highbeams on. I drove into some really thick stuff and hadn't gotten around to dimming my lights.

I'm running 100 watt Hellas in the High beams. I wonder if there is a remote chance the glare and reflection from the fog caused the photo optic switch to cycle?

GM Tech, what's your opinion?

GM-Tech · January 25, 2005

When the ambient light sensor fails, the headlights default to ON. While it's possible the sensor could have simply given a "it's light" signal rather than a full failure, I've never seen it. I don't know if reflection could do that. They require a pretty strong light signal to indicate it's daylight. Even driving under a bridge will cause the lights to come on.

There's no circuit breaker per se. The BCM controls relays that turn the lights on and they send power to the lights through fuses. I'm sure the BCM is protected against an overload condition but not by an old fashioned circuit breaker. Probably some sort of QUAD driver, but I don't have access to BCM internal schematics so I really don't know.