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KIcking out of gear a lot!

22K views 44 replies 8 participants last post by  texasduramax 
#1 ·
I bought a 2006 Sierra 2500 HD with 190k bone stock about 6 weeks ago. After I was driving home a couple hours later(I bought the truck in Pocatello Idaho and live near Olympia WA) the tranny kicked out of gear and threw a code. I went straight to the parts shop to read the codes. The codes are P0729 Gear 6 incorrect ratio P0567 cruise control signal and P0700 Trans control syst malfunction. From a stop I hammered down threw every gear with no slipping. It eventually quit throwing codes and erased them without being told to but the issue still continues. At first it just seemed to kick out randomly or over a decent bump but now does over a bump, letting off the fuel, no reason at all and sometimes wont go into gear from park. It is now so bad I barely made it home. Please help point me in the right direction because now I can not even drive HELP MEEE
 
#2 ·
Welcome to DF!

I would put money on NSBU Switch.
On the side of the transmission under your linkage.
LBZ's have one plug.
Have you gotten "Range Shift Inhibited" on the DIC yet?
 
#4 ·
PO700 is a generic code..
Theres more to it, you'll need a better scanner to figure out exactly.
But my money is on the NSBU Switch, use the search tool and check out the threads.
There is a lot of information on that switch and its a common issue.
Its $120ish, and a two beer minimum job.
Good Luck!
 
#5 ·
I searched here and other places for those codes but found no similar issues to mine. I have not searched that switch but will do so now and come back here after I find something. Thanks for the info because I feel like I have been smashing my head against a brick wall.
 
#8 ·
You see your gear indicator on your DIC?
When you tried to put it into reverse for example, did the little line underneath "R" disappear?
 
#10 ·
Hmmmm
Others may have to chime in, but I sticking to the NSBU Switch being the problem..
There are ways to test it, but I am not sure. I replaced mine with the same symptoms as you.. But I do not want to steer you in the wrong direction as well though..
 
#14 · (Edited)
It is NOT the NSBU switch as the 6 speed does not have one. They use a Mode Switch that is inside the trans, and does not give much trouble like the NSBU switch

Possible the transfer case is worn and it looses the speed sensor when going over bumps. You need to monitor the speed signals with a Tech II- when it happens.

Moved to Trans for more help.
 
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#16 ·
When you say looses the speed sensor when going over bumps, what do you mean by that? I am really curious as I think I have symptoms like this in my "brand new transfercase"
 
#15 ·
Ahhhhh crap
Sorry man, I am in my own little LB7 world and totally forgot that....
My bad....
 
#17 ·
The transmission speed sensor is in the back of the transfer case, if it looses the speed signal, it can affect trans shifting. Check the big plug in the back of the trans-- make sure it is in all the way and secure. Follow the harness and look for shorts a wear. Of course make sure the trans fluid is in the middle of the hash marks while warm and running.

Drain the transfer case and look for metal- check the output shaft for up and down-- and in and out movement.
 
#18 ·
Fresh fluid, just did a double drain and fill
Now if any of those sensors were bad or the transmission is slipping, won't it throw some kind of code?
Output shaft is tight, no movement what so ever.
Fluid was just replaced for the first time since reassembly, looked normal, will do another change again to insure.
 
#19 ·
Like jc said prolly the transfer shitting the bed. My friends did the same thing and a week later it grenaded going 80 down I 70. Tore shit up.
 
#20 ·
Welcome..... Olympia truck here as well. We do have a hidden gem up here in Washington.I know it is a shitty feeling having something wrong with a new truck.. I am sorry but...

Sdp up in port Angeles is one of the best duramax/Allison guys in the country. Maybe trailer or run the truck up to him
 
#22 ·
I run synthetic tranny fluid in mine.. Torque Drive
Its only a few qts

The fluid will have a little metal hue to it but you should see no flakes.
 
#23 ·
I bet the tail shaft bearing and copper or brass (can't remember) ring is gone. When you hit a bump it's moving and not lining up for the speed sensor and throwing the code. Don't drive it or you'll risk damaging the driveshaft and possibly busting your fuel tank and lines.
 
#25 ·
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#28 ·
Have you drained the oil yet?
Three things make it leak, bad ring/bearing, worn yoke, or a bad seal.
 
#30 ·
Make sure you at least check it. If you can't feel it with the first joint of your finger it's low. I have smaller fingers and if I can't touch it with my second pinky knuckle I won't drive it till I add oil.
 
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