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Discussion Starter · #1 ·
Ok, where to start.

I purchased a 02 Trailblazer with 4wd about a year ago. Within a week of owning it the Service 4WD light came on and continues to come on when its cold and I cant shift into/outoff 4wd. Dealer recommended replacing the switch which didn't solve the problem. So through the winter I left it in AWD and this summer (warm outside) 2WD. Sounds like a common problem from info on here.

A few days ago I thought I noticed the fron axel pulling when in parking lot when turning sharp while in 2wd (service light off since its warm). Thought I was just mistaken until starting it up today and it automatically switched into 4 HI. Hmmmm, wierd right. In the next couple minutes the AC fan quit blower and I had an electrical smell. Then it began again but only when on Hi.

Gonna take it to the Chevy as this sounds expensive and encompasses different things. But though Id see if anyone had experienced this also. Could it be a computer?

Thanks,
Matt
 

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I purchased a 02 Trailblazer with 4wd about a year ago. Within a week of owning it the Service 4WD light came on and continues to come on when its cold and I cant shift into/outoff 4wd.
Oh, you should have found trailvoy then. :D
Dealer recommended replacing the switch which didn't solve the problem.
Idiot dealer. In other shocking news, the sun will rise tomorrow in the East. :crackup:
So through the winter I left it in AWD and this summer (warm outside) 2WD. Sounds like a common problem from info on here.
Well, yes. But since it wasn't the switch, it could have been the TCCM, the front axle actuator, or the transfer case encoder motor. One of the best cheap ways to diagnose that is to be listening to the motors underneath as you change modes. Now it's warm, we won't have the benefit of that trick.
A few days ago I thought I noticed the fron axel pulling when in parking lot when turning sharp while in 2wd (service light off since its warm). Thought I was just mistaken until starting it up today and it automatically switched into 4 HI.
With the switch in 2HI it moved by itself into 4HI? EIther the dealer's new switch is flaky, or it needs to be exercised through all its positions a hundred times or so to clean the contacts. Or the TCCM is flaky. Many 2002 TCCMs were bad, and were replaced. There is also a dealer reflash to make it more reliable waking up from being turned off and going to sleep. But the symptom of this is NO lights on the mode switch. Do you ever observe ZERO lights on the switch?
Hmmmm, wierd right. In the next couple minutes the AC fan quit blower and I had an electrical smell. Then it began again but only when on Hi.
This isn't related to the 4WD problem. DO you have the automatic or the manual HVAC control? What speed was the fan control on if it was the manual control?
Gonna take it to the Chevy as this sounds expensive and encompasses different things.
Why would you do that when the goofballs couldn't even diagnose the 4WD switch properly?
Could it be a computer?
If you count the TCCM as a "computer", then yes it could be. But it's certainly not either the BCM or the PCM, the really, really expensive ones. :sadcry:
 

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Discussion Starter · #3 ·
Wonderful info, thanks.

When it was cold I dont recall hearing it trying to shift. The switch light was on until i tried to change it when it was cold. Then the switch light would go off.

Yes, it changed itself with the switch still in 2wd, the 4hi light came on and was in 4wd.

Manual AC, and it was blowing hi when the fan stopped. Cut it off and initially wouldnt come on. Then off again and then come on in hi only.

Sounds like I need to find a tccm to try ... does that stand for something?

Thanks Again:thx
 

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TCCM is the transfer case control module. Run a search here for pics on where it is. Ebay is a good source of them.

Your other problem is very likely a $30 blower resistor pack, if the blower itself didn't jam with a dead mouse nest in it or something. The burning could be the wiring harness from the vehicle TO the resistor pack. That's a $60 item. Read the thread on changing the pack, and then take a look to see if you have charred wiring in the connector.

http://forums.trailvoy.com/showthread.php?t=50141
 

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Oh, you should have found trailvoy then. :DIdiot dealer. In other shocking news, the sun will rise tomorrow in the East. :crackup: Well, yes. But since it wasn't the switch, it could have been the TCCM, the front axle actuator, or the transfer case encoder motor. One of the best cheap ways to diagnose that is to be listening to the motors underneath as you change modes. Now it's warm, we won't have the benefit of that trick.With the switch in 2HI it moved by itself into 4HI? EIther the dealer's new switch is flaky, or it needs to be exercised through all its positions a hundred times or so to clean the contacts. Or the TCCM is flaky. Many 2002 TCCMs were bad, and were replaced. There is also a dealer reflash to make it more reliable waking up from being turned off and going to sleep. But the symptom of this is NO lights on the mode switch. Do you ever observe ZERO lights on the switch?This isn't related to the 4WD problem. DO you have the automatic or the manual HVAC control? What speed was the fan control on if it was the manual control?Why would you do that when the goofballs couldn't even diagnose the 4WD switch properly?If you count the TCCM as a "computer", then yes it could be. But it's certainly not either the BCM or the PCM, the really, really expensive ones. :sadcry:
hi roadie, i just added this into another issue that i posted on concerning rattling noise. while i'm not experiencing the same problems you addressed, i do have the zero lights on my mode switch. i have an 03 envoy and thought that this may be a fuse issue (the zero lights), should i be concerned about this? i basically drive in 2wheel rear (i think:eek:) and use awd during periods of inclement weather (again i think, therefore i am:crazy::crazy:)
thanx, sanitcapt1:tiphat:tiphat:tiphat
 

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Discussion Starter · #6 ·
TCCM Update

Roadie, of coarse you've been right on.

The A/C blower is fixed and the TCCM has been replaced for $50 from the local junkyard with the lastest GM part number one. The 2wd, awd, and 4hi all work. Only problem is when switched to 4lo it goes back to AWD.

Im taking it for the flash update tomorrow when the dealership opens. Is that going to remedy this or shall I get another TCCM?

Thanks
 

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Roadie, of coarse you've been right on.

The A/C blower is fixed and the TCCM has been replaced for $50 from the local junkyard with the lastest GM part number one. The 2wd, awd, and 4hi all work. Only problem is when switched to 4lo it goes back to AWD.

Im taking it for the flash update tomorrow when the dealership opens. Is that going to remedy this or shall I get another TCCM?

Thanks
Did you do the switch cleaning as suggested by Roadie in post #2?
 

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Discussion Starter · #10 ·
Ongoing saga

Yes, while in nuetral.

Had the TCCM flashed and it's still doing the same thing. Will go through all except 4lo. When placed in it, you can hear the encoder motor move and the light shows AWD. Is there some kind of position sensor or something that could be doing this?
 
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