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Re: 2003 GMC Envoy Low beam headlights will not work.
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.
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If the lgihts go out when low beam is selected, both low beam lamps may burned out! It is possible that you drove the vehcile with one low beam not working and didn't notice. The second failed and now you noticed!
If not, there is a headlight relay that selects high/low beam current to the headlights, but those things seldom fail. Check your owner's manual to find its location and replace it.
Take a test light and test for power to the low beams. A common issue is that one low beam burns out, and the operator does not notice, but they always notice when the 2nd one goes out... MAy be just a bulb issue, and testing will confirm.
There could be a fuse for each low beam light either under the hood or under the dash. If not, then prob both low beams are bad.
If you have daytime run lights, the following may be of help.
There is a daytime running light module that controls both low beams and the daytime running lights. The low beam bulbs may be OK. The high beams will work fine as they are not controlled through the module.
It may be possible to disable the daytime run lights by cutting the yellow wire going into the module and then connecting it to ground. Tape off the other end. This will help. Thanks please keep updated.please do rate the solution positively .thank you for using fixya
You have a separate fuse for the high beams and the low beams. Fuses are located in panel in driver's side of dash concealed when door is closed, or in the power distribution box under the hood on the driver's side. You have separate lamps for each (not likely since they both went out together). The worst thing it could be, and it is very expensive for parts/labor (and you don't want to tackle this one yourself unless you are a good mechanic) is the column-mounted dimmer/cruise/wiper/washer/turn signal switch. The part alone is almost 200 bucks, and installing it requires dismantling the steering column inside the SUV. Hope it's not that.
The adjustment screws/nuts should be located either on the top of the headlamp assembly,
behind the headlamp assembly, or near the frame rail by the radiator
You will have vertical adjustment screws for each independent beam
(separate highs and separate lows, but will be same screw if highs and
lows are the same bulb). You may also have additional horizontal
adjustment screws as well
your car on a level ground 30 feet from a wall and measure the height
from the ground to the bulb and mark on a wall (do this for highs beams
and low beams if the bulbs are separate, if highs and lows are the same
bulb, only do it for the lows)
For Low Beams: If the headlights read VOR, then
aim the brightest part or cutoff part just below the mark on the wall.
If it says VOL or nothing, aim them 2 inches below the mark on the wall.
For High Beams (if separate from low beams): Aim the headlight directly at the line you marked on the wall.
check fuse and relay, if its good, than you have faulty switch, only work on low but not high beam, to turn high beam on the switch move forward which is fauty or no contact, flashing high beam move toward you which has a good contact and working. it two switch in one unit.
Check for headlight relay and fuse. Some cars have separate circuits for head light flasher and normal high/low beam. From your description, I would suspect a bad connection to/from relay or relay itself.