Hi,
I bought a new complete headlamp assembly for my 04 Rendezvous and my service engine light came on immediately after changing.
It only comes on in the daytime.
After dark, it is fine. I even went so far as to get a replacement unit and it stll does the same thing now.
It'* just when the vehicle is started in the daytime, as soon as I put vehicle into drive (which would activate the daytime lamps) the service engine light comes on.
Made sure bulbs are the same also.
Garage could find no error codes even with the service engine light on ???
Appreciate any input as I am stumped.

find the ground for the headlight make sure its good and makes good contact. does the drl light up when its supposed to?

Hi,
Any idea where the ground for the headlight is?
You've given me food for thought, that maybe when I took out the original the first time, I may have pulled too hard on the cabling.
All 4 lights come on in the daytime unless I cover the sensor with a dark cap ??
So no, DLR definitely don't seem to be working.
Appreciate your posting.

definitely sounds like something went wrong with the wiring, or sometimes if the bulbs dont get seated all the way it will do funky things. i haven worked on one of those before so i wont be able to give you any specific locations.

Thanks for your help anyway.
The vehiclew is going to dealer this week and I hate the thought of the possible cost.
Thanks again.

Maybe the shop is using a scanner that doesn't have access to vehicle/manufacturer specific error codes? The light being on should show some code if the scanner is able to read it.
If it has to do with the DRL system, a generic scanner may not be able to read it.
If you have an advance auto or autozone nearby, they might be able to read it for you. (Usually, their scanners can read more specific codes).

Might be able to check the fuse for DRL (should be labeled in your fuse box) and see if it is still good. If not, there might be a wiring short. If its bad, could try replacing the fuse and see if it holds. Sounds like the system can't activate the DRL, which throws an error code and turns the CEL on.

Not being familiar with the vehicle, I can't be of much more help.

I went and checked my FSM for my 04 LeSabre (not saying they are the same setup, but might be some help) in the DRL inoperative schematic, and there is probably a relay in there to look at as well. But try the fuse first.
Not sure which beams light up as DRLs either, make sure those work first. Check the easy stuff before taking it to a dealer, might save ya some money.

Is it the Service Engine Soon or Service VEHICLE Soon light that'* on? The SVS light is usually triggered by lighting problems..like blown bulbs.. and does not throw a code that can not be read using a normal scanner. Like SilverSleeper said, check the relays, and simple things first. Your automatic light sensor may have malfunctioned and is messing with the other things..