Transmission oddity

[markrinker]

Twice in over 50,0000 miles of service, each of my flatbed 3500 trucks has gone into what I will call 'transmission limp mode', once each. First time I was towing an empty trailer. Second time was towing 12,500lbs.

It feels like the tranny is stuck in 2nd, no upshift or downshift until truck is shut off and restart, where normal operation resumes. Park and reverse both operational, just no forward gear other than 2nd.

What causes this? Is it 'normal' or a sign of some maintenance needed?

[FarmerDale]

Mark,

Doing a search on this will reveal a couple other threads. I have the same problems - only when cold. The fault code referred to a sensor signal out of range so that the electronic controls on the tranny don't allow an upshift. I don't know what it takes to fix it, so my resolution has been as you did - shut off and restart. Works for me, but others complain when they get the problem and figure that the tranny is going...

[Dvldog 8793]

Howdy
My 99 was having same problems and throwing a code 1860 OBDII. It was some selinoid in the trans. I would clear the code and be back to normal. The problem ended up being a bad wire in the harness that comes out of the trans on drvr side and the bends back over the top to go to the pass side. The conector to the trans is where mine went bad. Could be a similar problem. Might be worth checking.
L8r
Conley Janssen

[Cowracer]

I also had the same problem. It was an input shaft speed sensor went bad. Easy $45 fix.

Tim

[markrinker]

Thanks - I'll check all of the above if/when it happens again. Once a year and I'll ignore it completely.

[Cowracer]

While checking, pull the shaft speed sensors. They are magnetic and attract shavings. After years, you can get enough 'build up' to affect the operation. My output sensor was like this, but my input was fried.

I cleaned the output and changed the input and had no more problems since.

T

[tanker]

After they replaced 2 solenoids in my 4l80E, it turned out to be a bad ignition switch at the bottom of the steering column. It would not make contact with each contact. Just my 2 cents worth. ;)
Let us know what you found. smile.gif