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Main headlights went out...brights and fogs still work

38K views 88 replies 40 participants last post by  Kimbra 
#1 ·
Hey fellow trailvoys,

Earlier this afternoon, I headed out and when the sun went down, I noticed my headlights weren't working. I checked my brights and fogs and they work fine.

Any ideas what could've happened? Could a fuse be the cause?

They were both working earlier today (I noticed them coming on when I used the remote to unlock the doors). Kind of strange for them to both go out at the same time...:confused:

Thanks :thumbsup:
 
#3 ·
The left and right don't share a single fuse. There is one for each side (#3 and #6). The first place that left and right lows come together is the underhood relay 46.

I could post a schematic if you have a meter and want to trace signals. Or give you some hints. But the relay may be it. Swap with the adjacent one of the same kind that runs the fan clutch. You can be without the fan for a few minutes.
 
#5 ·
Well,

Both the fuses are good. So when I switched the relays, the passenger headlight is on and the driver turn signal light is on. Both turn signals work when you try them.

Might be time for some new relays...I'll be back when I know more.
 
#6 ·
A bad relay alone couldn't cause those symptoms, since the low beam relay is shared by both sides. If your low beam driver's side lamp blew with a massive short, the fuse should have blown quickly to protect the solid state relay, but perhaps it didn't, and the relay is now damaged.

You may need one new relay and one low beam lamp. I usually buy two at once because if one blows for being old, the other one is usually close behind.

I haven't figured out a way that the headlight relay could interact at all with the turn/marker lamp circuits, unless there's a wiring harness short. Let's fix the headlights first, because those are a safety issue.
 
#7 ·
Just got back from my quest to find relays...I checked Advance, NAPA, Pep Boys...none of them have relays. NAPA is the only one who can even order them...for $49.99 apiece. Haven't ordered any yet...

I figured it would be a good idea to order 2 if I did have to order. Advance suggested me go to a junkyard...I'm not so sure because I could be getting a couple that are gonna go bad like mine??

I'm trying to avoid going to the dealer...figured it would be an arm and a leg to get some there.

If I need a new headlight, I have to replace the whole lamp, not just one bulb, correct?

Looks like I won't be driving around at night for a few days anyway...not sure the FL laws about driving with fogs only...:undecided
 
#8 ·
Low and high beams are separate bulbs.

Solid state relays are a very rare failure item. I don't carry a spare, and I'm usually a nut case about carrying extras of things I think will fail.

That relay (15016745) is dealer list price of about $45. gmpartsdirect.com has it for $25. Make sure you try cross-referencing it with Airtex 1R1944. Rockauto.com (one of my favorite vendors) has that for $28.
 
#9 ·
This is off of napafix that we use at work...may or may not help...good luck


Vehicle Application: 2003 Chevrolet Trailblazer 4.2L 2004 GMC Envoy XL 4.2L, Vin S, Eng Cfg L6

Customer Concern: There are no low beams or Daytime Running Light (DRL) operation. The high beams and flash to pass work fine.
Tests/Procedures: 1. In the underhood fuse box verify the HDM fuse to verify it is hot at all times.

2. If OK, then swap the HDM relay #46 with another similar relay and see if the lights start working.

3. If the lights do not work, check the Pink/White wire from the relay to the Body Control Module (BCM) for opens or shorts to ground.

4. If the wire is OK probe the wire to see if there is a square wave signal on the wire with lights commanded on.
Potential Causes: Open Fuse
HDM Relay
Wiring
 
#10 ·
Thanks for the help, guys.

I went ahead and ordered 2 relays (from gmpartsdirect.com---thanks roadie) I know one's bad for sure, b/c when I switched them, some of the lights did work.

After I put in the new relays, if some of the lights still don't work, I'll try getting new bulbs for them.

Hopefully that's all and not a wiring problem. After the relays come in, I'll post the results.

Thanks again.
 
#11 ·
Hey guys,

Well I had a little problem with FedEx delivering my relays to me (long story :x), but the good news is I finally got my relays over the weekend, and sure enough, it fixed the problem. Everything seems to be working fine now. :thumbsup:

Now, just for the hell of it, I wonder how this happened in the first place? If these relays are rare failures, I wonder what might have caused this....I do know that the day that my lights went out, I went through one of those drive-through car washes and I got the max treatment which does everything including the underbody. I wonder if some water got up in there and shorted something out?

Any thoughts?


Thanks guys, I've learned so much cool info from y'all over the past year that I've been a member.
:thx :thx :thx
 
#12 ·
Knowing a bit about how they're designed, there's nothing short of a REALLY strong static spark that should be able to take them out. Certainly nothing a car wash would normally give out, since humidity and soap films tend to dissipate static build-up. Root cause is going to be unknowable.
 
#14 · (Edited)
headlights random on and off

I have a similar issue with my headlights on my 03Trailblazer. The headlights turn on and off at random, but the driving lights and high beams work. You can be driving down the road and "off the lights go". But the driving lights stay on, a few minutes later the low beams come back on. Any thoughts? Tks Craig
 
#17 ·
I have a similar issue with my headlights on my 03Trailblazer. The headlights turn on and off at random, but the driving lights and high beams work. You can be driving down the road and "off the lights go". But the driving lights stay on, a few minutes later the low beams come back on. Any thoughts? Tks Craig
I have had the same thing happend to me!It hasn't done in a while,but of corse you know it will start happening again!
 
#15 ·
This relay- I think is solid state--- and not mechanical...
But- when something like this happens--- it may be heat or cold related...
in your case-- it may be heating up and causing a failure--- cools down- and works again...
But next time it happens- get out and jiggle that relay around--- or remove and put back in... no go?... replace with the fan clutch relay...
 
#16 ·
I will try, the lights usually go off when we are go down the road and unable to pull over. You think it could be the headlight swith?? Or I guess maybe the high/low lever on the column itself? Craig
 
#18 ·
Next time it happens take a blunt object and hit the side of the dash where the cubby hole is on the drivers side, with the door open. Fixes it everytime on mine.(I use a mag lite) I have chaulked it up to ghost wiring in the switch housing.FYI sometimes you have to hit it pretty hard, not hard enough to damage the dash, but HARD.:m2:
 
#21 ·
It's my turn now! My wife left something from work in the company vehicle and I drove her up there in the TB...just before we get there the headlights went out!?! They wouldn't turn on manually either. We left the TB at her work and had to drive the company car home. I figured I'd find something about this on the forum. I'll see if they work tommorrow, maybe they will cool off and work again? $49.00 relays, huh? We have a zero deductible Platinum Extended Warranty on it, I think I'll let them take care of this. I'm starting to think there is an electrical gremlin at work here...just a few weeks ago the anti-lock brake light came on one night and wouldn't go out...until the next day:undecided
 
#23 ·
Relays get corroded lugs and other things. Pull the relay and tap on it a few times, not hard enough to break the plastic housing. Plug and unplug it 8-10 times to clean up the lugs and see if that takes care of it. 75% or so of most problems are dirty connectors and dirty lugs.
 
#26 ·
Frankly, I never checked to see it the high beams would work. It was 830, and we had to drive 16 miles, so we just parked it and left. I tried the manual switch, and even locked and unlocked it with the fob a few times, but only spent about 2 minutes at most. If it happens again I'll be sure to see if the high beams work, as well as the driving/fog lights. The service manager at the dealer said something had to have happened to cause the PCM to shut down the lights, but advised me to see if the problem duplicated itself. As you know, electrical problems are often of such nature that if it's not happening at the time the technician is looking at it they just NPF (no problem found) it on the service order. But I understand, I know those warranty companies aren't going to pay them to spend a lot of time on the problem or let them guess which parts are faulty on their dime. That's why we purchased a good extended warranty to begin with, I knew with all the electronics on this truck something expensive was bound to fail. Never thought it would be the headlights though?!:eek:
 
#25 ·
I had the same thing happen twice now, most recent was last night. After I let it sit for 45 minutes to an hour all was well again. I was wondering about this though last winter I replaced the oem low beam bulbs with sylvania xtravsion bulbs when one side burned out. Could these be drawing too much and causing the relay to get hot?
 
#27 ·
Same question - was it the lows only that quit on you? There are two relays involved. The high beams use a traditional relay with contacts that could conceivably get hot, but it could also be the relay socket contacts. IF YOU HAVE A HIGH BEAM FAILURE: Best thing is to exchange that relay with an identical one next door if it happens again. Front relay 43 is the HI beams. Swap it with the identical one next door - 42, which is the windshield washer pump. IF YOU HAVE A LOW BEAM FAILURE: Swap relay 46 for the identical one - 45, next to it, which runs the cooling fan clutch.



The low beam relays are different, and more expensive, because they aren't the traditional kind with physical contacts inside, like this:



They are solid state (semiconductor) items, so they can be turned on and off at a much higher speed than normal relays. The fan clutch needs one of those to continuously vary its speed under PCM control, and the low beams need one to operate the DRL function. The daytime running light function actually turns the low beams on about 70% of the time and off 30% of the time, at hundreds of times per second. This is done with a PWM waveform (pulse width modulated) which you can Google for if you want more reading. It's the fast ON/OFF switching of the low beam relay that absolutely KILLS some lamps and all HID ballasts if you change from the OEM bulbs.

Frankly, I never checked to see it the high beams would work.
If it failed while you're driving in the dark I heartily recommend trying anything in reach. When I was in pilot training, at night, my instructor reached over and turned off the instrument lights and asked what I'd do. I calmly reached into my shirt pocket and pulled out a mini-maglight and held it in my mouth while I continued to fly the plane. He snatched it away and said, what next, wise guy. I pulled out mini-maglight #2 from a sleeve pocket. He snatched that. I pulled out my BIG maglight from my flight bag. He snatched that. I finally had to manage the plane's engine RPM and airspeed by reference to the engine and wind noise, not seeing any of the instruments. THAT was the lesson he wanted to teach me, not discover how many spare flashlights I was carrying within reach. :duh:
 
#32 ·
It's a solid state relay, which makes it more difficult to test, but also less likely to fail than the socket it plugs into. Just swap with its identical neighbor and see if the symptoms change. If you start to overheat at stop lights, the relay is definitely bad. (when you swap the lo beam relay for the fan clutch relay)
 
#33 ·
Clutch relay and low beam relay..

So what are the chances that the fan clutch relay and the low beam relay are failing at the same time.. I've been having the issues with the my low beams turning off randomly.. Now it seems as if my clutch is not kicking in.. When i turn on my a/c the fan does not spin any faster.. while driving down the road with the a/c on my trailblazer will start to run hot.. If i turn off the a/c it goes back to a normal temp... Autozone can order the relay for 38.99.. should i have them order 2 and replace both? Or could my clutch on the fan just be going out?
 
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