4L80E, not 4th gear or OD

[Michaeljp86]

Ever since Ive had this truck the over drive never worked, I did the TCC mod and thats how I lock the torque converter. When I bought the truck the transmission wasn't shifting into 4th. I changed the fluid, filter and shift solenoids and I was back in business but no OD. About once a year I would have trouble with it not wanting to shift into 4th gear. Taking the battery cables off would fix that, so something must have been throwing a code.

Now the no fourth gear seems to be here almost every day. Now im afraid to drive to far.

The fluid doesnt look or smell burnt. I just cleared the codes, next time it happens Ill see what comes up.

Any suggestions on things to check would be appreciated.

 

[NVW]

Could be a break in the harness giving intermittent power. There is an updated harness for the older 4l80E.
http://www.electricaladvantage.net/4l80esolenoidmasterkitwinternalharness.aspx
At the bottom it gives the part # for the upgraded external harness.

 

[WarWagon]

Pull codes out of the transmission computer. You know the one that tests the SES light at key on and then never turns it on again unless the engine stalls? It will have a wiring error code, ratio error code for internal trans issues like a bad sprag clutch, or nothing.

Nothing means the ECM memory power may be bad or something else doesn't indicate it should go into 4th.

Mis-Adjusted TPS is a common issue for lack of gears.

Check the 2 wire speed sensors for insulation falling off and shorting. One sensor in the front of the trans.

 

[bison]

The speed sensors should test the same ohms within an ohm or 2,..i believe around 23.