01 Yukon XL - blower & headlight - on then off ???

larryw · June 9, 2004

I bought a used 01 Yukon XL with 45K. All that I have replaced is the 4WD switch and an A/C box air filter. In the few months I have had it, it does this routine that I am really wanting to know about. Every once in a while, while the truck is completely turned off and not running, the front air blower motor kicks on at what sounds like high speed for anywhere from 5 to 20 seconds. As soon as it stops the headlights will flash on and off usually twice. This is all that happens. Is there a humidity sensor in the a/c box that kicks the blower on to keep the area more dry. I am really fishing here. If my guess was even close, I can't come up with anything for the headlights flashing.

We noticed this the first time when we were drying the vehicle after a good wash. Since the warmer weather is here and the a/c is ran more, it seems to happen more. It does not do this usually more than 3 times a day and even now sometimes now, not at all. So I am not concerned, (yet), about running the battery down.

Is this a message or some weird malfunction?

AZ-Z71 · June 9, 2004

Yeah, that is a feature that GM added to prevent smells for happening in the A/C system. It is a dryer that dries the system out so there is no condensation. It usually will run for a short period of time maybe a couple of cycles after the vehicle is shut off. I'm not sure if the vehicle actually came with this or if a previous owner complained about the smell when the A/C comes on, and had the dealer add it under the TSB for this. There is a TSB for this and this is the fix if someone complains to the dealer about smells in the A/C.

The thing with the lights, I heard that this happens sometime after this dryer is installed is installed at the dealers. I don't know if there is a fix for that or not but I have heard of it before. I think it has something to do with the way it is hooked up and the security feature of the truck.