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Discussion Starter · #1 ·
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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Discussion Starter · #2 ·
Is this still waiting on approval?
 
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