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2002 Chevrolet TrailBlazer:
3rd Brake Light not Working

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Alex Steele
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Question:

 

We have a 2002 Chevy TrailBlazer. This vehicle has always had problems with the brake light bulbs not working. The problem we now have is that the 3rd brake light, or high mount brake light, works but the other two don't.

 

Answer:

 

2002-2004 Chevy TrailBlazer tail and brake lamp problems resulted in a safety recall effective October of '04. The same recall also involved its GMC, Olds and Buick mid-size siblings. The issue was bulbs coming loose in their sockets, therefore becoming inoperable and a safety hazard. The repair procedure involved inspection and, if necessary, replacement of the left and/or right tail lamp circuit board assemblies.

 

But let's assume the recall was performed on your TrailBlazer and eliminate defective tail-assemblies from the picture -- for now. The third brake light (up top) functioning correctly eliminates the brake lamp switch at the brake pedal as a cause, because the same switch supplies all the brake lights with 12 volts of DC power. The third brake light coming on also confirms that fuse #12 (25 amp) located in the fuse block under the hood is good, and fuse #16 (10 amp) located in the fuse block under the left rear seat, which feeds power only to the third brake light, is also OK.

 

But in the same fuse block as #16 is fuse #34 (15 amp) which warrants a good look. This guy supplies voltage to the left and right side brake lamps. If it's burnt, replace it, but keep in mind that changing a burnt fuse usually doesn't fix the problem for good. The fuse will probably blow again shortly thereafter, and require a technician to trace and repair the short to ground which overloaded the circuit in the first place.

 

Also check to see if the directional and backup lights are working. That will confirm that their ground circuits, which are shared with the brake and tail lamps, are 100%. If you've found nothing to this point, remove the tail lamp assemblies and carefully inspect the bulbs and the circuit boards. Other than that, there's always the chance of an oddball break in a circuit due to a poor connection or a cut in the wiring harness.

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Comments:

TechHelp2
09 Feb 2019, 20:22
The Center High Mounted Stop Lamp (CHMSL ) fuse should be checked if the brake lights work. Also check the brake switch area, if the brake switch is malfunctioning the cruse will not work.The brake switch controls the brake lights and the cruise control function.
Sabrina
09 Feb 2019, 19:23
My upper brake light does not work and neither does the cruise control. Could it be related to each other?
TechHelp2
06 Jun 2017, 10:20
RE:Joann, Check your fuses for the brake lights if the fuse is good check your brake switch at the brake pedal for proper operation.
joann
05 Jun 2017, 20:08
Hi, Why are my 2002 trailblazer both left and right and middle tail lights not working? Please let me know if you know the answer.
Thank you Joann
Admin
10 Oct 2011, 15:27
The problem discussed above with the tail lamp circuit boards also affects the 2004 model year.

If the bulb is loose in it's socket, or power/ground is not being transmitted through the circuit board to the bulb, replace both left and right circuit boards.
Christne Brun
10 Oct 2011, 12:14
I have an '04 Trailblazer. The problem is with my driver's side tail light. I have replace the top bulb several times, but have noticed that when I unlock my car with key fob that top light does not come on like the other side. I know my brake lights work, it just appears to be that top tail light. Any help??
Admin
16 Jul 2011, 06:55
Start with the basics. Use a test light or a multi-meter and check for power and ground at the suspect bulb's terminals. Once you see which is missing, the circuits must be traced back to find the open or bad connection.

Very often the problem is right there at the light socket. If there's no power or ground at the bulb side of the terminals, check the back side.
George Fields
15 Jul 2011, 09:56
2004 Chevy Trailblazer and the rear passenger tail light won't work. Top light of the three blinkers works and brake light works. All driver side rear lights work. I checked fuses under hood, all good. Checked all fuses under passenger seat, all good. An all lights in good not blown condition. Please help me with this if possible. Thanks George F.

 

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