need 4l80e help

[cucv30]

Hello, i am working on a friends 91 K2500 that has a 4l80e. All it has is 2,3 and reverse. I'm thinking it must be something electrical. I wish i knew as much about these as i do the 4l60e but i haven't worked with them much. Anyway i unplugged the harness from the side and it acts the same as when it's plugged in. Strange thing is there is no SES light. I know it works cause it comes on with the key and goes off after starting. I drew the codes out and it has 59,68,81,82. My question is could it be the QDM and i need to replace the ecm? Anyway just looking for anyone who has experienced this same sort of thing. I did find power on one wire where the harness connects to the trans, but i have no idea if there should be more than one. Any ideas will be appreciated.

 

[Greg72]

Send a PM to Greg Ducato....

I'll bet he has the answer right off the top of his head!

 

[paratrooper307]

Saw problems like this a lot on 4l80Es when I was working on Humvees. When the ECM is not functioning properly or doesn't have power, the trans defaults to 2nd and boosts the line pressure, and won't shift. Check all power connections and fuses. These transmissions have a lot of trouble with input/output speed sensors. Here's a list of various DTCs.

http://www.trnw.net/z-search/4L80E.php

Good luck!

 

[cucv30]

Thanks i'll send him a note. Thanks paratrooper, you may be right cause the codes i drew up mention the quad driver module and if i'm right, that's part of the ecm.

 

[cuervo]

I had the same issues, but with different codes on my 91.

Turned out to be the A Shift Solenoid and the Manifold Pressure Switch. I replaced them and the trans was fine for another year. I had some more shift issues and it turned out to be the ECM. I replaced the ECM and it was good again.

Then, when I installed the 383, I just put in a completely rebuilt trans.


Oh, I never had a check engine light for the trans codes.

 

[Greg Ducato]

With the ignition on, check for 12 volts at the E terminal at the case connector. Check the trans fuse if no voltage is found. Check that there is not fluid leaking through the case connector. Check wiring at both front and rear speed sensors, it is often brittle and frayed. This could also be caused by extra accesories added to the electrical system or low voltage from alternator, bad battery connections or faulty ignition switch.

 

[cucv30]

Ok i'll do that but i didn't see a fuse that was marked trans. It has had a new harness put on it sometime so i will check those connections as well.