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Do you mean the night-time backlight, or the FIVE that indicate what mode you're in?

If NONE of the mode lights are on, you have a problem with the TCCM (transfer case control module) or the fuse. Not just the switch. Check fuse #8 under the hood.

Are you sure no other dimmable lights are off, like the heater control panel or the door switches? It could conceivably be a problem with the dimmable instrument panel circuit.

Does the 4WD system change modes when you turn the switch? (i.e.: make noises underneath the vehicle like it did when it worked OK?)
 

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2002 chevy trailblazer_lt
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sounds like what happened with mine, you need to go to the underhood fuse box and reset the TCCM by pulling its fuse for 30 seconds and replacing it, it will either start working then or it will still not work and the service 4x4 light will come on
 

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Could be a bad fuse, or pulling the fuse for 30 seconds might reset the TCCM, or it could be a bad TCCM, or you could benefit from a reflash of the PCM software to get a patch that increases the reliability of the TCCM waking up when you turn on the ignition.

With the ignition on, but the engine not running, try pulling fuse 8 for 30 seconds, then putting it back in. See if the lights wake up then. If so, the reflash is the highest probability problem. If not, then look for a used TCCM on Ebay or in the junkyards. Trade first with a local trailvoy-owning friend if you have one to confirm the fault.
 

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Discussion Starter · #6 · (Edited)
pulling the fuse for 30 sec worked. i have another question it dont have anything to do with my last question on my fuse box under the hood i have a treaded post that dont have anything on it like the others and there is a red wire that is tied off that has a circle conecter on the end i was wondering what it is its not tied off of the fuse box its tied off another group of wires
 

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2004 gmc
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Great news!

The stud feeds one of the seven wires going to the trailer wiring harness. If you hook it up, one of the wires gets a constant 12V for trailer battery charging while underway. If you don't tow large trailers with their own batteries, leave it off.

The studs nearby are for the Megafuse, which feeds the rear fuse block. Sometimes, owners loan the car to goofballs who use these threaded studs for jump starting, and then the megafuse blows and then the owners come to trailvoy to find out about that one.

You can search for "trailer battery charge stud" or "megafuse" and learn more if you're curious.
 

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GM could have saved a LOT of questions and confusion, especially here on trailvoy, if they had only put a label on that wire as to its purpose. Owners have even asked some dealers' service folks, who mostly have no idea.

Trailvoy knows all .... tells all.
 

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What happens if the infamous fuse #8 (ADC) is pulled and left out? Does it control anything else, besides the TCCM? The reason I ask is that I have had 4WD problems 3 times now and pulling the fuse to reset it has always worked - for a while. The problem I have is that it will attempt to shift or actually shift to low lock. No rhyme or reason when it happens and last Monday it attempted a low lock shift at about 50 mph - you should have heard the noise. Usually, it has shifted into low while starting it up and sitting in park. I had the 4WD fuse under the back seat pulled (figured I don't 4WD for the summer), the service 4WD light was on in the dash cluster, but it attempted the low lock shift anyway. I plan on taking the '02 Envoy on vacation next month and would like to be sure it cannot attempt a low lock shift. Will the #8 fuse (ADC) pulled insure that the 4WD will not work? Will anything else be affected? BTW, the ole girl has 168K on her, and has been a great family truckster. Thanks.

pm
 

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4x4 not working when cold

Just posted this in General section but here it is again. I have a 2002 Envoy.My 4x4 does not work when the vehicle is cold. Below zero at the start of the day. I have no light at the control and the 4x4 service light is on. When I preheat the interior or if I run the SUV with the interior heat on for about 30 minute it will work after a restart.I know it heat related because I have no problem with it from spring to fall. GM says its the control module behind the control knob by your right knee and it $500 for the part. Any ideas.:ugh:
 

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4x4 Interior switch

Has anyone seen a red " N " appear, I started My Envoy one morning and as always let it warm up. I noticed the 4x4 selector was blinking, 2 HI so I tried turning it to 4 LO 4HI nothing happened but a little RED N appeared on the switch. then I put the truck in Drive than in park and it went away, can anyone tell me What's up with this? thanks Jay from Maine
 

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Probably a dirty switch. Have you been regularly exercising it and the 4WD system to make sure it will work when you need it? Anyway, I've been recommending a monthly test of the system (remember the noises the various actuators make as well.) For this issue, turn the switch full CW and CCW with the power off a hundred times or so and see if it gets more reliable.
 

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2002 chevy trailblazer_ls
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Love the pic Roadie...

Should that stud for the trailer wiring have a nut on it if no need for trailer brakes? Mine does not, but there is a connector on that stud.


Thanks,
Terry B:thx
 

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I've explained this in more detail perhaps in other threads, but that stud has nothing to do with trailer brakes. It's ONLY used if your trailer has an on-board battery that needs recharging as you drive along. And if you put on the ring lug that's in the background of your picture, you will need a 6mm nut to secure it.

The ring lug on the base of the stud in your pic that's coming from the right is the FEED from the fuse block (there's a 30A fuse protecting this circuit). If you don't connect anything to the stud, there's no need for a nut.
 

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same issue with 4x4

I have to say just reading threw some of the forums on here have helped alot with the little issues i am having with me 02 tb. I have a question about the flash you are talking about. i pulled out my fuse #8 for 30 sec and then started my rig back up. all the lights came on, (they were not comeing on at all before before and there is no sound indicating the change from 2x4 to 4x4) but then they shut right back off. should i do that flash thing you were talking about? if so where could i go to have that done?
 
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