Re: Tow truck tranny issues, back again
 

Input speed sensor sounds very promising

Re: Tow truck tranny issues, back again
 

A stand alone TCU is a waste. There's no reason to need one or go through the hassle.The stock stuff works fine, there's several million dollars worth of R&D behind them for reliability. Adding some stand alone controller requires more wiring harness and adapting/interfacing that just adds complexity, and does not guarantee a solution.



It's more likely to be a wiring harness problem than an ECU. The wiring diagram for your truck can be found online, probably for free.



There are two ATSG manuals that are good for that transmission, one is a dedicated rebuild manual, the other is a manual that covers it and the 4L60E, and includes the electronic/electrical diagnosis.

Re: Tow truck tranny issues, back again
 

i was a GM service manager for many years, when we would see problems like this we usually found that the pin tension on the harness was not adequate for a proper connection. It is very important that you probe the terminals with the proper pin connectors, if someone used a test light or an ohm meter to check for continuity than they may have spread the terminals just enough to make for a poor connection. Make sure your shop has the proper tools to diagnosis this concern.

Re: Tow truck tranny issues, back again
 

You make a great point on the TCU. I'll research the manuals you've referenced. Waiting on rain to pass here so I can get back under it and swap the input speed sensor. Thinking about swapping the neutral safety switch as well. I found a new one yesterday that had been picked up for another truck that has been sold. Nice to find stuff I had long forgotten about. As long as it's the same part from 95 to 98 anyways. I'm optimistic. I'll pull up wiring diagrams as well. Thanks for the info.

Re: Tow truck tranny issues, back again
 

I'll certainly keep this in mind. Thanks.