Any 4l80 Gurus?

Jon9116 · May 31, 2019

Calling all 4l80e experts. I have no 4th gear. Background info. No CELs. My transmission cannot be commanded electronically via scanner or manually with the valve body wired directly so all signs point to tranny. All transmission solenoids are within spec via GMs ohm chart. All other gears are smooth. Also, on scanner, trans shows to be in 4th when in 3rd and 3rd when in 2nd. All forward gears show 190 PSI (no way of checking 4th). Any ideas?

Edited May 31, 2019 by Jon9116

davester · May 31, 2019

See if there are any TCM codes. You need a code reader that can read codes from the TCM. And just because the CEL is off, does not mean there are no codes.

The CEL is defined to come on when one of the many computers in your truck has noticed an emissions-related problem. It flashes when there is a current, ongoing emissions problem happening.

While I have rebuilt my 4l80e, I don't have any experience with figuring out problems with it (the original transmission worked fine, and I rebuilt a used 4wd-version of the 4l80e prior to installing it and the rest of a 4wd system in my truck).

Edited May 31, 2019 by davester

dtnel78 · May 31, 2019

IF you have a capable scanner check in under transmission and look in there for codes. Depending on the scanner you have there may be some tests you can do. Another thing you can do if you plan on keeping that transmission awhile is get a ATG book for it with all the detailed charts, tech information, etc. I bought the ATG and another one that's a tech guide for each vehicle I have. Downside to working on transmissions can be getting into them without the specialty tools needed for disassembly and assembly as well. Report back and let us know what you find.