4L80E No overdrive...sometimes
 

I have a 91 Crew Cab single wheel 1 ton with a tbi 454 and a 4l80E transmission with a 205 transfer case. The issue I am having is that sometimes it will either slip out of overdrive and wont go back in or wont go into overdrive at all. When it wont go into overdrive it will not lock the converter either. It shifts 1-3rd just fine all the time and does not seem to be slipping ever. I have read that the pass through electrical connector can sometimes be cause for issues and will check that first. Just wondering if anyone else has had these issues and what was done to correct them, or if there are any transmission experts that can give me some direction/advice.

Re: 4L80E No overdrive...sometimes
 

Pull the governor and see if it is moving freely......

https://www.youtube.com/watch?v=Szkx3OCkScM

Re: 4L80E No overdrive...sometimes
 

That is for a 700R4. My transmission is a 4L80E. My suburban has had issues with the governor and I can tell you if the gear fails on that going down the highway that gets your attention. 4th to 1st gear right now.

Re: 4L80E No overdrive...sometimes
 

http://67-72chevytrucks.com/vboard/s...d.php?t=668062

Read through this thread, I think it describes the fix to your problem if you've got a lot of miles on it.

Re: 4L80E No overdrive...sometimes
 

bump

Re: 4L80E No overdrive...sometimes
 

Does the problem show up when the truck is pulling load ----- going uphill or towing?

Do some searching under "actuator feed limit valve", which involves the valve body. Another possibility is a slipping torque converter clutch.

These are tidbits I've happened across, and I'm by no means any kind of authority, so just take 'em as something to look in to.

Re: 4L80E No overdrive...sometimes
 

Finally got time to look at this again and pull some codes. I got code 68 and code 85. 68 appears to be something with the a/c. I am not concerned with that at this time. 85 is either a prom error or the transmission speed sensors from what I can find. If anyone knows how to test or can verify this please let me know.

Re: 4L80E No overdrive...sometimes
 

Well after some more digging I found the wires were bare at the front speed sensor. I cleaned them up and got them separated and taped up enough to go for q test drive. Trans shifted perfectly and never did its thing of falling out of overdrive. I am still getting the code 85. Some sites say it is a prom error and others say for a 91 it is a trans issue. Cam anyone confirm any of this?

Re: 4L80E No overdrive...sometimes
 

...

Re: 4L80E No overdrive...sometimes
 

I guess I am not sure what to expect if the ECU had a PROM error but the truck seems to run perfect and shift perfect so I am going to call it fixed.