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2003 GMC 2500HD CCSB 6.6l Duramax 148k Miles 1 Winter in MN, Montana truck
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4 Posts
Discussion Starter · #1 ·
Hello New Member as of today although I frequent these forums quite often. Very useful and informative and helpful folks here.

My issue is my trans temp. It says it's over heating when it isn't. I have used a laser thermometer and it stays around 130-160ish not towing and the weather is around 70 degrees. The gauge has been acting up sometimes showing 0 temp or 200-300 overheating with the warning lights.

I have had the Pressure manifold/temp replaced, internal wiring harness, ign switch, and my cooling stack is clean. New batteries, I checked the pins on tcm harness and dielectric greased. Also cleaned up the ground under driver door, added another ground wire back of engine (where the aluminum mesh wire is) and boy im stumped. Wiggled wires, etc... I thought it was fixed just now when I went to gas station it was reading just about 150 degrees left it running came out hopped in and literally watched it go up to about 200 maybe and drop to dead 0. Transmission shifts fine through all gears. No check engine light right now. But the previous codes I was able to pull beforehand that pertain to this are a U1000, P0700, P0711. I'm thinking it's the TCM acting up just not sure how to test it I have a multimeter though. What do you guys think?
 

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Registered
2003 GMC 2500HD CCSB 6.6l Duramax 148k Miles 1 Winter in MN, Montana truck
Joined
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4 Posts
Discussion Starter · #2 ·
Quick update:
I ended up buying a new TCM programmed to my VIN#. Installed with a small amount of dieelectric grease after using electrical contact spray on the harness connecters. Prior to installing the new TCM I cleared codes disconnected negative cables on batteries. After installation even more codes came up with shift range inhibited, I let the truck run for a few minutes to hopefully let it recognize the sensors, shut off and cleared codes. Restarted went for a short drive less than 10 miles and everything seems fine AS OF NOW. No CEL, and temp gauge is working properly. Shifts are a little wonky, but with careful driving for a while the Allison should relearn the correct pressures to smoothly shift. I will update later on today after a much longer drive, and several key cycles.
 
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