Gearbox Fault--Again!

[troverman]

More of this saga: some of you may have read the last post about the whole gearbox fault message, the limp home mode, clunking, no upshift / downshift, etc. Somebody said trans was toast, but no, the next day it was fine. I thought it was some wires getting wet from trans ecu, taped them, and the problem did not recur for some time--until today! Snowy day in NH, and the whole limp home deal again. So obviously the trans does not fail mechanically then magically fix itself the next day--but what is going on? Most of the time its fine, but wet and snowy (mostly wet) weather seem to make this fault manifest itself. In addition, the fuel gauge went from nearly full to empty, the message "fuel gauge fault" is displayed, then guage goes back to proper reading and message disappears. There is nothing wrong with BeCM.

[OkieRover]

I hate gremlins like this one.
When I wash my engine bay...my alarm goes off when I lock the doors. What is it with these things?
Okay if I am going to apply my work to my hobby I would say unplug the computers and clean the contacts on the plugs. Maybe spray some di-electric grease on them before hooking them back up.
Moisture is the problem, I would try to eliminate moisture.

[Moto One]

Look for a loose ground, start at the batter, then at the fuse block. When you have multi function failing a ground is the first suspect. Through in the cold/wet, It might be the ground wire that has been bent too many time and has a small fractur that brakes contact with cold shrinkage.

[shiftech]

Check your battery,I had a dud cell but didnt notice as the truck starts as soon as you turn the key.I got "gearbox fault" alarm then the truck was stuck in 2nd gear.As the battery got worse so did the alarms,axle,AES,temp.
Got me and my bank manager worried for a while .only found it after soaking the eletrics then trying to crank the engine the battery died straight away.Grounds are another good place to look.My box fault would clear if I turned off the ignition and restarted.

[troverman]

Battery is large and new Interstate, problem is in fact those dumb wires going into the transmission from the harness! One is a coaxial type, with the braided wiring just under the sheathing, and two more insulated wires inside. As engine RPM's get to the right spot, engine mgt computer sends signal to trans ECU to shift into next gear. Because the coax cable insulation was gone it was contacting another exposed wire and signal was diluted. The shift wasn't happening, RPM's would keep climbing, and the ECM would notice and slam the gearbox into 4th gear where it would constantly stay. It is zero fun starting off in 4th gear on a steep grade with cars behind you. Accel. is floored and you're barely crawling! This wire is nastly to patch up, upside down under the truck in a rotten spot, but now is perfect again. By the way, if any of you get gearbox fault, shifting into low range and then back to high clears it, if only temporarily, it will start off in 1st again.