New ride won’t shift correctly

Good morning all
first off I’m new to this forum so hello all

Anyways, a few weeks ago my brother picked up a new HMMWV from gov planet with the 6.5L and 4L80E. Finally got her home and have been going through it to work all the bugs out. The vehicle is very clean but is having one huge issue....it doesn’t shift. When we start it up and it’s cold, it will drive, make it to third gear, then drop back to 1st after about 30 seconds. Almost like a limp mode.

The codes its giving are 12, 85, and 87

We have replaced the speed sensors in the trans a t case, as well as throttle position sensor and calibrated it to the correct voltage.

Has anybody experienced this or maybe have any input?

thanks all

-Danny

If it shifts into 3rd gear it’s not in limp mode. You can only get to first and second in limo mode.

My guess is you have a problem with hard parts in the transmission and not the controller.

I would at a minimum check the fluid level and see if it’s burnt smelling, drop the pan and replace the filter.


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Here's a couple of service manuals that may help.

https://shop.ukrtrans.biz/wp-content/uploads/catalogs/4L60E_80E_CODE_BOOK.pdf

https://www.logsa.army.mil/psmag/archives/PS2015/746/746-16-18.pdf

https://www.steelsoldiers.com/attachment.php?attachmentid=678658&d=1493698092

Lots of other links on the google and lot to read, CAMO Just up the road in ROSAMOND.

Fluid looks good. I haven’t dropped the pan yet however. I’ll do that and see how it’s looking there

Those codes wouldn’t mean something electronic or something with a sensor?


And thanks. I’ll do some reading

Take a look at the third link I listed above. There's a lot going on with 4l80E's. The info is very in-depth. My quick review, I would look at page 122 after all the simple battery and grounds inputs are met. Good luck.

Simple when it all works, CAMO