2004 Envoy, low beam headlights turn off on their own.

It's the headlamp relay #46. If you want to test it, swap it out with the cooling fan relay #45 and see if your headlights work. If they do you know this is the fix. Found the solution online a couple of years ago and it was spot-on. The part was $45 at autozone at the time.

Duplicate post

Headlight Replacement (Envoy)

Lift hood, at top of each headlight assembly look for two L-shaped tabs. Pull these tabs straight up, this will release the headlight assembly. Lift assembly forward to gain access to rear of assembly. There two rubber caps, the top one is for access to the low beam and the bottom for the high beam bulbs. Remove the appropriate cap, grasp bulb socket and turn CCW to release. Unplug bulb from socket by releasing catch on side of socket, install new bulb, DO NOT touch bulb glass with fingers. Reverse steps to re-assemble.

Other possibilities are; the bulbs themselves, burnt or corroded bulb sockets, or a bad headlight selector switch.

Depends on model, most of GM products now have seperate beams for low and high, and some high beams require a different headlight for proper brightness.

check the bulbs the low beam elements may be blown

If high beams work and low beams do not, then it is probably the high/low relay. It is part number 15016745 and has four prongs. To test if your relay has gone bad locate the relay in your fuse box. There will be two of these relays located next to each other. One controls the low beam headlights and the other the cooling fan. Swap the relays and check your low beam headlights. If the low beams work you have a bad relay.

Lift hood, at top of each headlight assembly look for two L-shaped tabs. Pull these tabs straight up, this will release the headlight assembly. Lift assembly forward to gain access to rear of assembly. There two rubber caps, the top one is for access to the low beam and the bottom for the high beam bulbs. Remove the appropriate cap, grasp bulb socket and turn CCW to release. Unplug bulb from socket by releasing catch on side of socket, install new bulb, DO NOT touch bulb glass with fingers. Reverse steps to re-assemble.

Replace Relay #46 in the underhood fuse panel.

You headlight lamp have a diffuser mechanism which allows it to flip between the hight beam and low beam feature of the bulb. In fact, you high beam will function even if the low beam is not working.

I would recommend the purchase of the new headlight lamp. It would cost you you any where from $15.00 per unit to get a replacement lamp