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  #1  
Old 12-02-2010, 03:35 PM
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Default 1999 LT Blazer with 4x4 Auto - 4x4 problem won't shift at all or shifts on it's own

weirdest thing ever

often times pressing any of the buttons on the dash switch will not do anything. nothing flashes or lights up, nothing is trying to engage.

other times it will try to shift on it's own out of 2wd into 4auto, 4high or 4lo. just randomly.

when it does engage into 4auto the whole front end of the car shakes when you accelerate.

all these issues happen at random, not a single consistency between them.

sometimes when i start the truck it is in 2wd and other times when i start it it's in 4auto, 4hi or 4lo even though it was in 2wd when i parked it.

unplugging the TCCM (i think it's called) brings it back to 2wd but then shortly after it tries to engage into any of the 4wd positions at random. sometimes it actualy engages itself and other times the light just blinks and it stays in 2wd.

seems i have no control over anything that happens unless i do something like disconnecting the battery or TCCM, but even then the problem comes back quick.

i got the truck used with only 100k km on it (60k miles) and I know for a fact the person I got it from (old asian man) never used the 4x4 for anything like off roading or what not. He said the whole time he had the truck it was always in 4WD AUTO, he was the original owner.

any ideas anyone?
  #2  
Old 12-02-2010, 08:24 PM
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Sounds familiar, something similar happened to me a few months ago. I changed the switch on the dash and it fixed my problem. However these have also been known to have problems with the 4wd computer in the right kick panel
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Old 12-02-2010, 10:01 PM
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Not sure if you will havea vacuum switch on the tranfer case seeing you said you have a 4auto button. If you do, its a cheap part that was bad on my 97 blazer and caused a similiar problem.
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Old 12-03-2010, 07:43 AM
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forgot to mention, the service 4wd light is lit up like a christmas tree all the time every time.
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Old 12-03-2010, 10:02 AM
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The NV236 (4-button w/ Auto4wd) does not have a mechanical vacuum switch on the transfer case, but rather an electric vacuum solenoid on the firewall to engage the front axle.

I would check the electrical connections at the switch (dash), the TCCM (behind the passenger side kick panel), and the encoder motor (on the transfer case near the front driveshaft) for signs of corrosion and clean as required.

Also, you can check the resistance at the switch. The NV236 Wiring Information thread will give you the values you should be seeing.

If the Service 4wd light is on, you will need a Tech2 or equivalent full featured scan tool to pull the codes from the TCCM. The light is telling you that there are stored codes.
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Old 12-03-2010, 01:49 PM
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yah i hope it's only electrical

what if i took off the dash switch, would it help narrow down the problem in any way?
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Old 12-03-2010, 02:26 PM
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I had this same problem on my 99 a few years ago; it turned out there was some water damage in the computer module (TCCM) behind the passenger kick panel that was causing intermittent shorts. Swapped it out with one with the boneyard and have had no problems since. It was pretty evident by looking at it that water had gotten on it so maybe take a look at that.

Module from boneyard cost 60 bucks or so.
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Old 12-03-2010, 04:04 PM
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Quote:
Originally Posted by Tinted View Post
yah i hope it's only electrical

what if i took off the dash switch, would it help narrow down the problem in any way?
It likely is electrical. The only way to narrow down the problem is to start testing. We can't do that part for you.
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Old 12-04-2010, 05:06 PM
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Update:

Last nite wihle plugging the TCCM back in I noticed it wasnt clicking. none of the lights on the dash switch were coming on either.

i thought TCCM broke. so i went and got a new dash switch and new TCCM today, plugged them in.........and nothing, no clicking and no lights on the dash switch. seems that TCCM is not getting any power at all. I took the multimeter to the plug in the kick panel and it's not getting any reading at all, i think it's supposed to be 5v signal or something? but I get no reading whatsoever. and the service 4wd light stopped coming on.

now im thinking the root of the original problem might have been weak power supply to the TCCM, and now there is no power at all.

is there a fuse or a relay i should check? I checked the 4wd fuse, it's fine. not sure if there is a fuse or relay under the hood i should be looking for?

Last edited by Tinted; 12-04-2010 at 05:19 PM.
  #10  
Old 12-04-2010, 07:30 PM
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Guys, I'm new to this site, but use many others similar for snowmobiles, Trailvoy.com for the wifes truck, etc. I'm diagnosing the exact same problem that Tinted is describing above. The dealer said the TCCM was shot, so I picked up one at the junk yard and put it in with no change. The switch seems dead, the front diff is locked in, but no control of the transfer case. The service 4wd light is on when either TCCM is plugged in. My next step was going to replace the transfer case motor, but I've been told I will still have to have the TCCM reprogrammed once I've done that. Is that true? Thanks-Jason

Update, same truck same transfer case...NP8, NV236.

Last edited by tntfaguy; 12-04-2010 at 07:47 PM.
Old 12-04-2010, 07:30 PM
 
 
 
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1999, 4x4, 99, auto, blazer, blazertrouble, c0308, chevy, code, k, problems, series, shift, shifting, shooting, tahoe, wrong


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