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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

#3 of 171 2003 Trailblazer Headlights Out by pdesimone

Jul 02, 2007 (7:05 am)

I have a 2003 Chevy Trailblazer. Just recently, both of my headlights went out. Whether I have it in the automatic position or if I put them in the "manual on" position, they don't come on. When I put on my brights, they work. At least they got me home. I'm sure I pissed some people off though. Anyway, does anyone have any ideas of where to look. I checked the fuses. There is a different fuse for each headlight and they both look OK. Could it be the bright switch, and if so, how do I check it? Looking forward to any help you can shed on the subject.
Thanks
Phil

#5 of 171 2003 Chevy Trailblazer Headlights Out by pdesimone

Jul 02, 2007 (7:58 am)

Sorry if this went out twice but, I'm not sure what I did.
Anyway
I have a 2003 Chevy Trailblazer. Just recently, both of my headlights went out. Whether I have it in the automatic position or if I put them in the "manual on" position, they don't come on. When I put on my brights, they work. At least they got me home. I'm sure I pissed some people off though. Anyway, does anyone have any ideas of where to look. I checked the fuses. There is a different fuse for each headlight and they both look OK. Could it be the bright switch, and if so, how do I check it? Looking forward to any help you can shed on the subject.
Thanks
Phil

#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

Messages Page 2 of 18

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