I own a 2003 Chevrolet Trailblazer EXT.

When I put my car on reverse back-up lights do not come on. I checked the fuse box in the engine compartment & changed the light bulbs, but the problem still exist.

What else can I do to fix this problem? Thank you & have a nice day:p

These issues can be simple as bulbs, but if not then it can get tough, not 100% sure here, but I believe the trans range switch sends a signal to both bcm and pcm and the bcm commands the bu lites, without a real wiring diagram , tough to tell. I assume you checked for 12v and ground at the sockets. Alldata.com has complete online manuals for 25.00 for 1 year access.

Didn't the 2002-2003's have issues with the lamp holders/sockets for the rear lense assemblies? Hopefully it's just that. A quick check for a functioning trans range/mode sensor is watch the PRND321 dash lights. If they flicker, flip around at random or dont line-up with what you selected with the floor shifter, you've got a range sensor issue. I believe it's internal to the trans on the 4L60E. A bad range sensor will make the trans shift in failsafe mode which will give harsh shifts.

Joel

I think that light issue was primairly for the brake lights not working.......I could be wrong though.

Correct, but it is possible the bu lites could be affected hence the prior suggestion to confirm 12v and gd at the sockets.