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Chevy TrailBlazer Headlight Questions

171 messages,  Last post on Oct 13, 2012 at 9:15 PM

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Messages Page 2 of 18

#6 of 171 Re: 2003 Chevy Trailblazer Headlights Out [pdesimone] by tblazed

Jul 03, 2007 (6:45 am)

Replying to: pdesimone (Jul 02, 2007 7:58 am)
Low beams are driven by a module in the underhood fuse block. #46 is the Headlight Driver Module ("HDM") which is a solid-state relay. This is becoming a common failure. You can test it by temporarily swapping it with #45 the "Cooling Fan" driver module for the fan clutch as they are the same type device. If that's it you will likely have to buy the replacement from a GM dealer. Prices can vary from about $25 to over $40 for that module depending where you buy it. Good Luck!

#7 of 171 Re: 2003 Chevy Trailblazer Headlights Out [tblazed] by pdesimone

Jul 05, 2007 (8:57 am)

Replying to: tblazed (Jul 03, 2007 6:45 am)
I swapped #45 with #46 like suggested, but my headlights still don't come on. What are the chances of both modules going bad? #45 is the "Cooling Fan" driver module. When I swapped them, the main fan still went around. I don't know if it controls the speed of the fan or the fan all together.
What are the chances of both of my low beams going out at the same time? Is there a highbeam/lowbeam switch on the column and could that be bad? How would I check this? Can I check the low beam with a test light. I'm trying to check everything before I have to go to a Chevy Dealer.

#8 of 171 Re: 2003 Chevy Trailblazer Headlights Out [pdesimone] by tblazed

Jul 06, 2007 (6:48 am)

Replying to: pdesimone (Jul 05, 2007 8:57 am)
The fan will still turn. The driver module for the fan controls the amount the fan clutch is engaged and the fan speed. There is a minimum amount of drag in the clutch so even at minimum it will still turn, just not very fast.
 
The headlight driver module (HDM) is controlled by the Body Control Module (BCM) under the back seat via a pink-white stripe wire that connects to the HDM pin 5 under the hood. The headlight switch signals the BCM to turn on the headlights. There are a few tests you could do to narrow it down to the BCM but that would involve shorting the pink-white stripe wire at the BCM or pin 5 at the HDM to ground, which will make the HDM turn on the headlights. DO THIS AT YOUR OWN RISK! You should be able to pull up the HDM slightly to get under it to pin 5, then with a suitable clip lead to ground and probe like a piece if solid wire, touch the pin. Be aware that there is direct Battery 12V on pin 2 so don't accidentally short that pin to ground or sparks will fly! You could also test both headlamps by taking them out and checking with an Ohm meter. Should read near zero Ohms. Pretty unlikely though that both would fail at the same time. Likewise with the two fuses.
 
Since yours is a 2003 it shouldn't have a HDM fuse #53. I believe that fuse was added in late 2004 but you might check for that anyway to make sure.

#9 of 171 Re: 2003 Chevy Trailblazer Headlights Out [tblazed] by pdesimone

Jul 10, 2007 (11:55 am)

Replying to: tblazed (Jul 06, 2007 6:48 am)
Thanks for the info.
Before I dove into the BCM, I decided to check for juice at the bulbs themselves. I seemed very unlikely that they would both blow at once, that's why I didn't check it right off the bat, but that's what it was. On the 2003, it looks like it's hard to get to the bulbs, but it was easier then I thought. The passenger side, I had to take off the cover for the air filter and I could reach my hand in. In any case, two lights and only $16. later, it was all fixed. Now, why did they both go at once. I had noticed a slight dimming a couple of times in the near past and I read somewhere that the Trailblazer had some alternator spiking problems. I guess I'll have to keep my eye on it.
Thanks for your help.

#11 of 171 '04 Trailblazer headlight problems by tayag08

Aug 10, 2007 (10:21 pm)

I have had two different mechanics check the headlights out on my car, and I've yet to have any luck getting them fixed. The bright lights always work, but the dims sometimes go out. Sometimes I can turn the car off, turn it back on and they work. Other times, they don't work for a while, and even sometimes, I think they're going to work and they go out while I'm driving. Has anyone experienced this problem or know how to fix it?

#12 of 171 Re: '04 Trailblazer headlight problems [tayag08] by svmilam

Aug 30, 2007 (12:21 pm)

Replying to: tayag08 (Aug 10, 2007 10:21 pm)
I have a 2003 same problem trying to find the solution

#14 of 171 2005 Trailblazer Headlight Problems by lvenema

Apr 12, 2007 (8:09 am)

My 2005 Trailblazer has had an intermittent problem with the headlights dimming since it was new. It usually only happens shortly after the engine has started after sitting quite a while. It happens after the vehicle has been driven for a few miles, the lights are on auto, and the heater/AC is on max blower speed.
 
The last time it happened was during a snow srtorm. I had just about everything electrical turned on and it dimmed the lights off and on for about 30 minutes. It seems like the electrical system can't put out enough power.
 
The dealer has applied fixes in all applicable TSBs with no fix. GM Tech support says this is normal? Somehow I just can't see that it is normal to have lights dimming while you are driving down a dark highway.
 
Anyone else have problems like this that have been fixed?
 
Thanks,
 
Lou

#15 of 171 Re: 2005 Trailblazer Headlight Problems [lvenema] by shoes2

Oct 23, 2007 (1:06 pm)

Replying to: lvenema (Apr 12, 2007 8:09 am)
Lou
I have a similar problem. Occasionally while driving down a road and lifting off the accelerator the headlights begin to flicker almost like going from a high bean to a low beam. I haven't noticed it happening with any special accessories on or off. Since its dark in the mornings when I drive to work now I notice it more often. I haven't bothered taking it to the dealer since I think it would be a waste of time. I'm actually not even sure if it both headlights or just one, but whats happening is noticeable and probably puzzles the oncoming drivers.
 
Dick

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