Limp Mode P0700 P0776

Starfire47

New member
Jan 20, 2021
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Looking for input with an issue I have been chasing my tail on.
Have a 2003 Chevy Lb7, has a generic canned tune (bully dog?) from the previous owner. 4" Exhaust, New injectors, K&N Intake, 35" tires, 230,000 miles
Never had any issues with the truck, have put 70,000 miles on it since I've owned it generally towing a car trailer or 28' snowmobile trailer.
Randomly just a few days ago while tipping into the throttle coming on the interstate the truck felt like it went into neutral, RPMs shot up and I let off the throttle and it felt like it came back into gear... I eased back into it just to get up to speed and it threw itself into 3rd gear limp mode, CEL etc. I was able to take some back roads to get it home and plugged my solus scanner into it and pulled the code P0700 and P0776. I've been through the wiring at the TCM, checked wiring for any exposed copper or abnormalities at the NBSU switch.
Fluid doesn't smell burned, and not gritty, but does appear yellowish I'm guessing from the age of the fluid. Im ordering fluid, internal filter and spin on filter today to see how the pan looks inside.
Does anyone have any recommendation on where else to check before suggesting Trans? Should I replace the Shift solenoid related to the 776 code?
Any help is appreciated!
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
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Phoenix Az
if your truck is 4wd, could be the t-case is shot and creating speed soensor issues, could a wiring issue or could be you lost the p2 planet splines. will it not go into 4th gear at all? as in, shifts 1, 2, 3, then ZING every time?
 

Starfire47

New member
Jan 20, 2021
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if your truck is 4wd, could be the t-case is shot and creating speed soensor issues, could a wiring issue or could be you lost the p2 planet splines. will it not go into 4th gear at all? as in, shifts 1, 2, 3, then ZING every time?
Truck is 4wd, It will go into every gear if Im easy on the throttle once its in 4th it holds just fine. If I get into it hard on the 3-4 upshift it almost stutters and bounces rpm around 2000 then will lock itself back in 3rd gear. 4x4 works as it should and is fine while Im plowing.
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
17,712
226
63
Phoenix Az
Truck is 4wd, It will go into every gear if Im easy on the throttle once its in 4th it holds just fine. If I get into it hard on the 3-4 upshift it almost stutters and bounces rpm around 2000 then will lock itself back in 3rd gear. 4x4 works as it should and is fine while Im plowing.
that dont mean much. check the speed sensor and see if the tone wheel has hit it at all. verify the wiring is good too
 

Starfire47

New member
Jan 20, 2021
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Pulled the speed sensor, no signs of contact. Wiring checks out from there from what I could see. Going to pull the connectors from the TCM again and have another look as well. Trying to check all the cheap fixes before digging into trans.
 

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