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Posted By: tydlifuk '93 Chevy based Winnebago - transmission issues - June 01st 2022 1:02 pm
Hi everyone,

I came by this site while looking up some diagnostic information regarding 4L80E in my pals '93 Chevy Winnebago 6.2 liter diesel (LS3 engine I believe)

The thing is stuck in limp mode, most likely for some electrical issue. I do have an ALDL diagnostic cable and bought license for the GMTD software which I use with it. However my previous experience with ALDL are from TBI engines.

The GMTD drops random numbers on the Input Speed reading (-2000s as well as +400s and +3500s) while the engine is idling, which would most likely be the issue of the limp mode (the transmission is stuck at 3rd or 4th gear). Before I got hands on 4L80E code book pdf which contains loads of useful information, we tried replacing both the sensors (input & output) as they were both old and not that expensive. When the situation didn't improve, I used my multimeter to take AC readings off of the wires leading to the PCM, which was pretty much okay - about 6 VAC idling, 13.5 VAC at higher idle. The van has no tachometer, but I guess the higher idle would have been somewhere around 1000 rpms. Most importantly, the readings were constant rather than random as they were in the GMTD software.

Now I am wondering, is there anything else I could check before deciding the PCM is faulty and getting a spare one? Is there maybe a different software that could hook up into the diesel PCM? I have TunerProRT, but I have no .bin/.ads/.adx files for the diesel.

Thanks and have a great day!

So we have managed to get it shifting again, with some help from another discussion site.

Turns out two pins on the inside of the transmission (accessible after pulling the pan) were bent a bit and the connection was loose. It took some cleaning and straightening, but the thing shifts like a charm now!

Hopefully this will help someone in the future ;)

Well thats good and will keep that in mind.
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