2003 gmc Envoy Low Beam Headlights both quit at the same time. Checked fuses and replaced bulbs. No dice. ????

Before you replace the #46 HDM relay (in the fuse block under the hood) try exchanging it with the #45 cooling fan relay and see if your low beam lights work. If they do, the HDM relay (actually solid state module, not a relay) is bad.

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

The problem is a Headlight module. Fuse box under the hood has two black modules side by side, the one on your right is the headlight module the one on the left is the fan module. Try swapping them, if the headlights work replace bad module, don't drive vehicle with the bad module in the fan slot. Mine kept going bad because I had a high intensity bulb on one side.

it may be a blown fuse check the fuses in the fuse box, you may find that HIGH & LOW beam lights have separate fuses..........hope this helps.....cheers.

If you have checked and discounted the relay, the only things left are the headlight switch and the wiring and to the headlights. Try the switch first. It is not impossible that both bulb's low beam filaments may have fused at the same time, unlikely but not impossibly. (It will not be fuses, unless two fuses blew together).

If you are handling the bulbs with your bare hands that is why your bulbs keep blowing out. use a washcloth to put the bulb in or rubber gloves, anything that will keep your hands from touching the bulb.

Both low beam head lights are burnt out? blown fuse.

Check your headlamp relays under the hood, should be located on either the L/H or R/H fender well , could be inside a black plastic box labled fuses and relays... there will be a label on the underside of the lid to this box locate the relays as per lables... please rate my help thanks...

I would start by checking the headlight relay and headlight fuse.  You also may wanna check to make sure the bulbs aren't blown out.  If those parts check out to be fine and in working order, you may need to replace the turn signal assembly in the steering column.  This part controls the hi/low beams.  This may sound crazy but, when GM wired their older trucks, they wired the headlights to go from the battery, to the hi/low beam switch, then to the headlight switch (to the left of the steering wheel) then out to the light bulbs.  You can kind of test to see if this part is good by making a fist and (with your headlights on) gently hitting the plastic cover for your steering column that is right behind your actual steering wheel.  This could cause your headlights to flicker on and off.  It's not 100% guarenteed that this method will work, but it may.  
Any questions, just ask!

no the battery does not have to come out the grill in front must be removed .yhis grill runs through the headlight lens there ore 2 sqaure clips that hold the lens pull up on them slid out lens and get to the bulb should be 9007 bulb number.