4L80E in limp mode...HELP

[metalman]

I've got a 6.5TD, 4L80E truck that has been nothing but awesome for two years, no issues. Been adding armor over the last 2 months and just took it for a drive last night and the trans light is flashing and it's in limp mode. Checked the big cannon connector on the TCM first thing and it was loose, thought that would be it. But it's still in limp mode so I let it sit overnight hoping it would magically be better today but no go.

As the truck sits right now, the only thing I've done to it since before this happened is wash the engine with Gunk and currently the airbox boot is off of the airbox, so I suppose it's getting more air? Also the two heater hoses are disconnected at the heater and capped off temporarily as the a/c is going in next.

I'm real good and bolting stuff together and making it look nice, but know nothing about the mechanics of the sensors, etc. on these trucks. It's ready to paint and I need to get this worked out, any help would be greatly appreciated.

[Urban Camo]

did you check the breaker on the panel behind the commanders seat.
You should find a resettable circuit breaker there.
Are you sure your connections in the battery box are tight.
Is the wire tight at your 14 volt tap on the voltage regulator.
All your grounds tight.

[Urban Camo]

you really should have a copy of all the TM's for your vehicle .
Send me a PM with your email address and I'll send you a PDF of the 4l80E transmission manual.
It has a nice trouble shooting diagnostic section
UC

[metalman]

thank you for the help, I'll check all of these things. PM sent with email address.

[metalman]

I just tried a brand new TCM, no change. Also checked the connections on the batteries and 14 v. output on the alternator, all tight and no change.

This truck does not appear to have a breaker.

[metalman]

We're changing the batteries now just in case they might be it, they are very weak and need a jump box to start. I'll update in a few minutes.

[metalman]

Put new batteries in and problem solved, the batteries were shot. Thanks for the help

[Action]

There should be a relay and a circuit breaker inside of a panel attached to the rear of the battery box (in rear seat foot area). You should just see a red button sticking out to reset it. Disconnecting the batteries may have just reset the breaker.
There is an unused port on the front of the TCM. With starter switch in OFF, you can use a paperclip and jump A and E holes. Go turn the switch to Run. The light will blink 2-digit codes. 1-2, 1-2, 1-2, x-x, x-x, x-x, etc, 1-2, 1-2, 1-2. The manual will show you what each code means. You may want to pull the wire to stop glow plugs from warming up. Unhooking batteries resets the codes, though.

Jason

[metalman]

Thanks Jason.