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2002 gmc envoy_sle
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24 Posts
Discussion Starter #1 (Edited)
i have done a lot of searching and cant figure out what the problem might be. i have an 02 envoy that the a4wd and 4wd has been working on and off. i first noticed when i got stuck in very little snow coming out of the drive way, only one wheel moving. it will go in sometimes after switching back and forth through all the modes. but most of the time i will have to drive a little while and try again later. when it does go in to a4wd or 4wd it will stay for most of the times. i check before go in the house everytime, and on a few occasions, it had come out. all the lights are working, and will blink till solid, even if it is not working. not due for a fluid change for another 15000. it hasnt been above freezing here in quit some time, i dont know if that might be contributing to the problem. i am open to any suggestions
 

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2002 chevy trailblazer_ltz
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2,063 Posts
My thought would be either a flaky TCCM (a very well known issue, particularly for 02's) or the encoder motor.

Hopefully someone like Roadie, who knows the 4WD system backwards, will chime in.

Matt
 

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2002 gmc envoy_sle
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24 Posts
Discussion Starter #3
i am hoping its something like that and nothing major, which i don't think it is, because when it does work, it works fine with no noises.
 

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2004 gmc
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26,181 Posts
Biggest initial question, is: When it fails to function, do the mode lights on the switch match what you command, and light up steadily?

I wasn't clear from your post if the lights are OK when it's failing to give you 4HI.

If your lights are OK, then the TCCM is satisfied that the encoder motor and the front axle actuator are in the commanded positions. Then you are left with mechanical failures in the transfer case or the front axle splined disconnect.

Run this flowchart:

http://www.offroadtb.com/articles/tech-docs/what-is-wrong-with-my-4wd-system
 

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2002 gmc envoy_sle
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24 Posts
Discussion Starter #5 (Edited)
yes the lights are ok there is no continuous blinking or anything like that. when it does engage it works fine, but sometimes it may come out again. and i will have to switch back and forth between 4wd modes for a while to get it working again. also there is a "clunk" noise but after the envoy is started (about 30 seconds maybe after a start) but still in park and it could be in 2wd or 4wd when it does it. but it is quick and nothing seems to change after that. for example, it has done it once this week. it sounds like its coming for closer to the passenger side.
 

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2002 gmc envoy_slt
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32 Posts
I'm having a similar issue. I'll try the flowchart when I get time, but I would like to know what your answer turns out to be.
 

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2002 chevy trailblazer_ltz
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the roadie;1052743 Run this flowchart: [url said:
http://www.offroadtb.com/articles/tech-docs/what-is-wrong-with-my-4wd-system[/url]
Thanks for posting that Bill. :thumbsup::thumbsup::thumbsup::thumbsup:

Matt
 

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2002 gmc envoy_sle
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24 Posts
Discussion Starter #8
well i had to today to check the 4wd thoroughly, it seems the problem i with front axle splined disconnect. its still working after a couple tries, but when i grabbed the shaft to move it around it seemed like there was a lot of play, it would move about 1/4".
 

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2002 gmc envoy_sle
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Discussion Starter #10
well i finally got it apart. it is most defiantly the front axle splined disconnect. every thing in there but the fork and one washer was chewed up, even the cv shaft. ill to get some pics to show you the carnage. waiting on the parts then hopefully it will be ready to go again.
 
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