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94 4l80e limp mode

S

silveradoTornado

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I did some reading on other posts but never really found an answer.

I have a 94 2500 with a newly rebuilt transmission, I put the tranny in about 8 months ago and have put about 4k miles on it so far. Everything was going just fine then they other day as I was driving down the road it went into limp mode. If I shut the truck off and start it back up it runs fine for 10 minutes then it's right back into limp mode.

The SEL is not currently on I did check the codes with a paper clip and I came up with 33 44 & 86

Should I put a new VSS to start with or is the code 86 a result of the truck going into limp mode?

86 (1994-1995) Transmission input/output shaft speed, ratio variation – lower than expectedWiring, input shaft speed sensor, output shaft speed sensor, mechanical fault
 
Grounds, check all grounding connections and the plug at the transmission too.
Thats about all I can tell You about the situation, and, only because of what everyone else says. 🤷‍♂️😹😹😹
 
I was busy all weekend I left it sitting with the battery unhooked for the last few days I am going to work on it again tonight. I believe those were the codes I was just going from memory on that. I do know it had the 86 code for sure though. I will get it all back hooked up tonight and report back. I am guessing that the codes will be cleared after sitting with no battery?
 
So I hooked the battery back up all codes were cleared. Drove to town and back and when I was just about back home it went into limp mode. Checked and I didn’t have power to the fuse. With the truck running I pulled the fuse and put it right back in and it was powered again. Same issue though drives fine for about 10 minutes then right back into limp mode.

Anybody have any thoughts?

I did pull the transmission plug and clean it real good then put it back which didn’t help.

should also add it now has codes 81 & 86 only
 
I did a little searching and found this old thread. Maybe something in here will help. I didnt read alla way through it.

Code 81 and not shifting out of first

I had this in the trcuk section and didnt get much help. Maybe someone who hangs out here would know. I get code DTC 81 - Transmission 2-3 Shift Solenoid Circuit. The truck has reverse but wont shift out of first. The transmission probably only had 500 miles in it when this happened. I put new...
www.thetruckstop.us
 
I was wrong yesterday I thought I lost power at the fuse when it went into limp mode, I was testing it and there wasn't any power until I reset the truck. I guess my tester didn't have a good ground while I was testing continuity. I thought it had to be the ignition switch as that was a common issue for others with the same problem. So I rushed to the parts store and grabbed an ignition switch and installed it only to find out I still have the issue, I did exactly what I said I wasn't going to do and that was throw parts at it. I guess today I will start testing and tracing wires.

At this point I think I have read every possible thread on the internet about this issue, there's alot of good info out there but 95% of all the threads that were started were never finished. So I plan to keep this one updated with my findings to maybe help someone else out down the road.
 
The one thing that has me puzzled is why will it reset and work fine for 10 minutes then go right back? It’s like clock work I would think if it was a wire short it would be a little more sporadic and intermittent. Is it possible that a failed solenoid would behave like that? Maybe the vss? I thought I read somewhere you can swap the front one and the back one to test?
 
Our resident transmission guru on here is @THEFERMANATOR . Now that I tagged him, he should also chime in shortly, as he's also a Moderator on here, also. I'm surprised that @MrMarty51 didn't right off the bat, must be his Oldheimer's kicking in! :smuggrin: BTW, welcome to The Truck Stop. You'll find a lot of very knowledgeable 6.5 owners on here happy to help.
 
I haven't given up yet just been too busy to mess with ol red thunder, it's just a farm truck and not my daily so it's not hard to just put it on the back burner. I will be sure to keep this thread updated with my findings. I am hoping to work on it next week.
 
Do you know what all was done during the rebuild? Was the AFL valve upgraded with the transgo(preferred) or sonnax valve? Were the original shift solenoids re-used and if so were they the screened ones? It can take a certain number of shifts or time for some codes to set.

I know sonnax makes recalibrated shift valves to help with this code and a few others.
 
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