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Discussion Starter · #1 ·
Tried posting in Transmission Shop...

Hi all,

First time I have had an issue with this truck.

2009 chevy silverado 2500hd duramax with allison
199k miles
at Diesel mechanic every 6k for maintenance.

The facts:

Driving normal at slow speeds (City road) when check engine came on. Gear selection P,R,N,D disappeared. (Don't automatically assume the NSBU switch, read on....)

Pulled codes with Bully Dog tuner (run it in no power, unless towing). Code was generic P0700. Since my tuner won't pull transmission codes, I headed straight to my mechanic. Truck would not shift out of 2nd gear. I cleared codes to see if it would shift to get to mechanic. Codes deleted, truck still would not shift out of second, even when I tried in manual mode. Dash Range slector did come back, and his not disappeared since. Parks Works, Reverse works but with high pressure (Slams into grear, with a delay), and Drive starts in 2nd and won't shift (Slams into gear with a delay). Drove to mechanic at 25-30 mph (trans temp at 165 on dash).The truck did not code again the entire drive.

Mechanic pulled history codes from Allision, and showed "overheat codes." He said multiple codes for overheat only, nothing else. He let the truck cool overnight. In the morning, the temp sensor on the dash was ---- (not registering). Mechanic changed temp sensor by dropping the pan and replacing. Also said the fluid was good level, not burnt, and no metal. He confirmed the sensor was working, but still same issue (stuck in 2nd). He drove to try to recreate code, but no codes. New temp sensor is now not working, but my BullyDog tuner is reading the Temp.... (this one has me scratching my head.

My mechanic thinks its the TCM, since it is not throwing any codes.... I unplugged the connectors on the transmission 1 by 1, and that sent a code to the TCM. Would reconnect, clear codes, and repeat with the next connector. I removed the TCM fuse, and got a code for lost communication, replaced fuse, reset. So Im not convinced its the TCM, and truck still stuck in second. I originally thought this was limp mode, but it is in 2nd (confirmed by 3 different computers), does not limit RPMs, and No codes....

Perhaps the NSBU switch... but again, no codes, no "range selection inhibited" message, and the truck responds to shifting from P,R,N,D.....

Any ideas?
 

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Suspect that you have a bad TCM. When mine went bad I had some of the issues as you.

CEL, tranny wouldn't shift out of first, tranny indicator disappeared. Dealer could not find any codes on mine either. Experienced mechanic at the dealership guaranteed that the TCM was bad or I wouldn't have to pay the labor and parts for it.

TCM was in fact bad on mine.
 

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Discussion Starter · #3 ·
Thanks @JimmyD. I finally bit the bullet and bought a preprogrammed TCM from Ryan’s Diesel Performance. I will install in 3 days when it gets here and see if it resolves the issues or at least gives me codes to chase after.

I’m still scratching my head on it will throw codes if I unplug connectors and force it to code. And how my tuner can see the temp but the dash cluster (digital) doesn’t register it. $503 for the TCM, but hopefully it gives me more information to work with.

Thanks for the reply.
 

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Discussion Starter · #4 ·
I got my preprogrammed TCM for Ryan’s Diesel Performance today. Plug it into the truck and all issues were fixed. Took the truck for a drive to relearn the shifting points, and temp gauge is working again. Temp held as it should. Only weird issue was my time on my display was not working. Ended up finding another forum to fix that. Will keep everyone posted if any issues arise, but as of now, back on the road and back to normal.
 
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