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Discussion Starter #1
Having a issue with a 02 envoy. I have no lights on the switch at all and also there is no service 4x4 on the dash. I pulled the #8 fuse and still no lights on the switch. My question is with the key on and the idiot lights illuminated should I see a 4wd light on the dash cause I don’t see it at all. I’m thinking it’s either the switch or the tccm. Has anyone had a similar issue? Thanks
 

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2004 gmc envoy_slt
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The TCCMs on the 2002 models were flaky, see if you can find a 2003+ TCCM at a salvage yard.
 

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2006 chevy trailblazer_ls
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Similar Symptoms '06 TB

My 4x4 has been out for a while and I recently swapped TCCM with one from the wreckers ~No avail. I am not with the beloved beast at the moment as I was called out of town to work. I have been told that I may need to reprogram TCCM (other armchair quarterbacks argue this) Trouble is not having a trustworthy mechanic with a Tech 2 scanner.

I am in Edmonton, Alta. So far my only option found is to get a Tech 2 off Amazon to the tune of about $500 Cdn, all in. I already took it to the shop and for $120. was told to replace the actuator (done that ) and "flash" will cost another $700 with no guarantee that will solve the problem. These places have you by the short and curlies if you don't have the right tools. I replace all of my own junk so I might as well get a scanner as well. F'n technology :bonk:

I will update once I have resolved the issue ~best of luck and keep us in the loop if you resolve without the scanner.
 

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2004 gmc envoy_slt
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Scottytar - please describe as best you can the symptoms of your 4x4 not working, specifically the indications on the selector switch, what do you hear when switching to 4HI or A4WD mode, is Service 4Wd light on in the dash display?

BTW, if you got a TCCM from a similar model vehicle, it does not need to be programmed, that only applies if you buy a brand new one.
 

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2002 chevy trailblazer_ltz
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I had this same thing happen just after having my transmission rebuilt (2002 TB LTZ, 163k miles). When I took the vehicle in, my 4wd lite and 4wd were working just fine. The problem was that I had totally lost reverse. So when I picked up the vehicle and the 4wd selector lite didn't come on, I figured maybe a harness hadn't gotten plugged back in. (And no, I did not have ANY 4wd capabilities...but reverse worked great!)
Anyway, had the shop check it out before I left. Everything was plugging properly. They put their scan tool on it, and if I recall the error was no signal of some sort from or to the transfer case. Checked all the fuses under hood, and under rear seat. All good. After a bunch of testing, finally determined that when the harness to the top of the tranny was unplugged/plugged back in... the ground wire had broken. They took the connector apart, refreshed the ground lead with a new pin, reassembled the connector, and hooray! the indicator light and 4wd functionality were back in business!

On a side note.
From time to time, my 4wd warning lite would come on the dash when I was running with AWD or 4WH engaged. It always cleared (went out) when I restarted the vehicle, so I was having a heck of a time troubleshooting it, and just lived with it.
First oil change after the tranny rebuild, I was under the vehicle and checking on the harnesses that had been disturbed for the tranny rebuild, and again trying to figure out why that 4wd warning lite kept coming on at odd times. Along the left inside frame rail, a large gauge red wire caught my attention. There was an obvious nick in the insulation, as there was a big fuzzy glob of greenish corrosion on it. I grabbed ahold of it and discovered that there were only a couple? of strands of copper left to carry the current load. I cut it, cleaned up the ends, and crimped in a butt connector and heat-shrink tubed the whole thing. Not surprisingly, the 4wd warning lite was off when I restarted the vehicle. That was 11K and 4 months ago. I run the vehicle through its 4wd paces at least 1X a month just to keep everything lubed up and I have not had ANY 4wd warning lite issues since.
Hopes this helps!
 
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