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2002 chevy trailblazer_ls
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Discussion Starter · #1 ·
Google has led me here and I have read some very good threads about this problem I am having.

I have a 2002 Trailblazer and both brake lights do not work but the third brake light does. All other lights do. I have checked fuse #12 and #34 and they are not blown. The bulbs are still good.

I read about the recall on the tail light assembly. I called my local Chevy dealer and they said the recall was no longer open and I would have to bring it in and it would cost $90 to diagnose. So I found the part online for $20 and had one shipped. Alas, it did not work on either side.

So I have been reading up and there is a brake switch located on the brake pedal. Is it possible for that to be bad and still have the third brake light work? I really don't want to take it to the dealer and be charged a lot of money for a part I can get for under $20.

Any tips or ideas will be appreciated.
 

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Good troubleshooting so far. The pedal switch runs the third brake light, so it can't be bad.

How are you sure the fuses and the bulbs are OK? Did you check them with a meter?

You could have a ground problem, but that would affect other lamps, and the left and right tail lamp assemblies use different grounds anyway.

There is no simple failure that explains your problem. Since the CHMSL works, take your meter (I have to assume you have or can get one) and probe fuse 34. Many fuses are built so you can probe their contacts while they are plugged in, or you have to get a fuse tap to do the same. YOu just need to see if the brake signal is getting to fuse 34, or if it's going missing in the wiring between the fuse and the lamps.
 

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Discussion Starter · #3 ·
No I did not check them with a meter. I don't have one either but I can probably borrow one. How do you check them with a meter?

But what I did was take the same size spare fuse and switched them out, I think it is a 15.

With the bulbs I just moved them to another spot to see if they would function and they do.

Thanks for your help so far.
 

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Swapping them like you did is OK. Some folks just look at them visually, and that's not a sufficient test. You should find a friend who knows how to use his meter, and pay him off with some beer. Then probe around fuse 34 to see if the brake signal gets there. If it does, then probe the bulb socket at the circuit board.
 

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If you pull the fuse, check it for resistance on the lowest resistance scale the meter has. Should read zero or very close.

With the fuse installed, I'd like you to check for voltage being present on each blade, while it's plugged in. It's very difficult to probe the bottom of the blades, but some fuses allow part of the fuse frame to poke through recesses in the molded body of the fuse. That's specifically so you can check voltages when it's installed.
 

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Discussion Starter · #7 ·
Thanks, I can definitely do that.

Unfortunately due to pressure from the wife I had to make an appointment at the dealership. Hopefully it won't cost me an arm and a leg to get this fixed.
 

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i would bet its the multi-function switch aka. turn signal switch assembly. just had this problem on my girlfriends sunfire. no brake lights only third. turn signals still worked. the part is about $50 from carquest i think.
 

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i would bet its the multi-function switch aka. turn signal switch assembly. just had this problem on my girlfriends sunfire. no brake lights only third. turn signals still worked. the part is about $50 from carquest i think.
don't want to throw water on your theory, but with the body control module, on these trucks, the multi-function switch doesn't play a roll. Sorry.
 

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Working on troubleshooting the issue right now.
He never came back to report, and only posted in this thread, and hasn't been back to the forum since. Don'tcha just HATE that? :hissy:

For you - start by checking fuse 34. If the CHMSL works, then it's not the switch at the brake pedal, and the designers sent the signals to the CHMSL and the side brake lamps through different fuses for safety and redundancy.
 

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I had this problem last night. All fuses checked out and had power to the taillights. I looked at the blubs and none looked like they were blown. I took a chance and replaced the brake light blubs. To my shock and happiness once the new blubs were in place the brake lights worked. I think I read somewhere that the brakes are the middle blub and that is wrong, it is the bottom one. So any one who runs into this problem in the future, replace the blubs first, they are cheap and can never really go wrong replacing old blubs anyway.
 

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same problem

im having the same problem...top brake light works fine but the left & right lights do not work. fuse #34 is ok but theres no juice going to the prons in the box. have any one figured this out yet?:duh:
 

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I would guess he means "prongs in the fuse box where fuse #34 goes".

If the CHMSL works, that means the brake light switch on the brake pedal works, and that fuse 16 is OK. But fuse 34 is connected to fuse 16 in the guts of the rear fuse block, so it's almost impossible that fuse 34 doesn't have power.

Take a short wire and wrap a bit around the blade for fuse 16. Then reinstall fuse 16. Then shove the other end of the wire into one side, then the other of the place where fuse 34 goes and press the brake pedal. That should bypass the open in the fuse block and see if the normal brake lights will work.
 

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First off, thanks for all the help and tips! I have this same issue of my brake lights not working on either side. I will add that the blinkers are working, wich uses the same middle bulb.

I first replaced the bulb, no luck.

Second, I confirmed that a signal is going through the fuse.

Third I confirmed the signal is getting to the Tail light ciruit assembly. I verified positive that 12v come through to the plug that goes to the circuit assembly when the brake is applied.

I thought the only thing left was to replace the ciruit assemblies, and did that tonight, NO LUCK!!!

Any other tips or ideas?

Thanks!
 

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IF and I do say "IF" you have 12 v to one side of the bulb then the other side has lost ground.
 

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Third I confirmed the signal is getting to the Tail light ciruit assembly. I verified positive that 12v come through to the plug that goes to the circuit assembly when the brake is applied.
Were you looking at Pin D, light Blue, which is next to the Black ground?

If it's at the wire, and not getting to the lamp, I'd guess corrosion or a bad crimp on the pin inside the connector. But you say this is on BOTH sides not just one. So that's less likely. Say, did you check the voltage on the pin with the circuit board plugged in?

No, I have another thought. I thought my Envoy was different enough, since we don't have backup lights in the taillight assembly, but the hazard flasher for me flashes the turn signal lamps, not the brake lights. You need to put a meter on the lamp socket that's connected to the light blue wire, whichever socket that is, and then see if you get voltage when somebody steps on the brakes.

The brake bulbs are separate from the hazard bulbs.

Perhaps you are changing the wrong bulbs.

If your other lamps are working OK, I wouldn't suspect the ground connection, because they all share one ground wire at the circuit board connector.
 
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