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Discussion Starter · #1 ·
Well just another day when you need the truck to perform- not a chance.

The 4wd auto track will shift from 2wd to 4wd auto and work fine.
When I try to select 4wd hi or 4wd lo the push buttons indicate it
made the shift but the front end is not working.
The buttons are lit and stay lit, but no spinning tires up front.
Shift back to 4wd auto and the front end will work hard enough
to pull thru 1 foot of hard pack snow but try to go back to 4wd hi and it will
not move, just the back spinning.
I have tried this on ice and snow all afternoon, with same results.
With the front end engaging it appears to be a t-case problem since
the buttons indicate it made the shifts.

The t-case actuator has been replaced just recently (1,000 miles)
and while up on jack stands all was well, making all shifts in and out of 4wd

Case is full of OEM auto trac fluid and all looks fine with harnesses and
grounds.

No noises from t-case and no leaks.

Anybody out there having this problem with auto trac shifting ?
Is there internals that can cause this partial shifting problem ?

It is very sad that my 1977 gas blazer has to pull this diesel burb out of
trouble all the time.

I am too po'd tonight to put it in the garage, but will put it up on
stands again tomorrow.

By the way has anybody know of a mechanical shift kit that can convert
auto trac to manual for just 2wd, 4hi and 4lo.
 

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Discussion Starter · #2 · (Edited)
Update,

The FWD is still not working thru all shifts.

The transfer case is shifting from 2WD to 4WDauto to 4HI to 4LO
and back again many times this morning.

The buttons on the dash lite up during each shift as expected,
doing the flashing while the shift is taking place and then staying on
at each respective button after the shift is complete.

The front wheels are only spinning in 4WDauto and not in the other
selections.

All fuses and harnesses look good.

Not sure if a signal between the front end actuator and the t-case is
the problem when in 4HI and 4LO, not sure what to check.

Any suggestions out there ??

Yesterday we had down pouring rain and today the driveway looks like a
hockey rink .

Sure could use this truck in working order.

Any help is truly appreciated.

Merry Christmas to all,

Tim
 

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Discussion Starter · #3 ·
Just another update,

The front drive shaft has power in the proper selections.

The front differential only works in 4wd auto and not 4HI and 4LO.

Is it possible something is commanding the differential to disengage in
4HI and 4LO but not in 4auto ????????

Hope one of Santa's helpers on DP can help with this trouble shooting
before the burb gets sent down the road to the land of unwanted toys.
 

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Discussion Starter · #4 ·
Burb is still not going into 4wd when selecting 4hi and 4lo.

It still works great in 4auto .

Any one on this site got any clues ??
 

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Discussion Starter · #5 ·
Looks like I am on my own on this problem.
 

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I was having all kinds of problems with my T case and found out that the np246 is always engaged so your problem will be in the front end.

hope this helps a little.

Ryan
 

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Discussion Starter · #7 ·
Any one have an exploded view picture of an auto trac t-case and
a wiring schematic of the t-case and sensors ?

Still trying to figure out the partial 4wd problems.
 

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I had a similar issue with my 99 Suburban.

In diagnosing the original problem (actuator motor on my t-case) the mechs tested the wiring by poking through the insulation. After finding the motor was bad they replaced it and I was on my way - for a while.

It turns out they trashed the wiring harness during the diagnosis and the case/controller was getting intermittent signals from the other systems on the truck. Sometimes it would work, othr times it wouldn't. I thought the 4x4 switch was bad at first until I tested it out.

The fix was to go throught the harness and test all of the connections and replace anything that looks questionable.

I had to replace a bunch of connectors and now it runs fine.

Hope that helps.
 

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Commissioner Gordon
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So you are saying the front axle is enguaging in 'Auto 4wd' but not in 4hi or 4lo??

This tells me basicly everything is capable of working, just something is not letting it work. The only thing in the system that controls everything is the Automatic Transfer Case Control Module (ATC).

Check for codes. No 'dummy' lights will come on, but there could be codes set in the ATC. If you have a code, let us know and we can go from there.
 

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Discussion Starter · #10 ·
No codes showing, checked every time I have used the vehicle with
OBD2 reader, no C.E.L. on since this started.

Yes the front wheels are working "only" in 4wd auto but not working
in 4HI or 4LO.

The drive shaft is engaging thru all three 4WD selections and not engaged
in 2WD , which I believe is the norm.

The t-case shifts smooth no matter which way I select the shifts,
whether I go directly from 2WD to 4LO, or 2WD to 4HI then 4lo, etc.

No noises to report other than the typical bump when going into 4LO.

The weather has been in the high 40's for a couple of days so I can
say it is not a cold weather thing, and the front differential is most
likely warm enough after driving for and hour to work to eliminate
cold fluids. All fluids are up to level and look good color.

Once again the dash buttons do their flashing while making the shifts
and then turn steady when the shift is supposedly done with 4LO
taking the longest.

I am starting to think this truck likes to be up on jack stands to take
the weight off of it's feet. Mother nature I assume is going to get
tired of this nice weather and start dumping on us soon. Was hoping to
do light plowing around the house only, but would now just be happy
if it would just pull its own weight.
 

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Commissioner Gordon
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Does your code reader read 'body' (B) codes? Most generic code readers only read powertrain (P) codes. This would be either a 'Bxxxx' code or a 'Cxxxx' code.
 

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Discussion Starter · #12 ·
I think it only reads "P" codes.

I call my son to see if I can borrow his SNAPON analyzer.
 
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