So I put gas in car and service engine light came on turns out cap was a little loose light didn’t go out. It is a new gas cap by the way. So I disconnected negative battery cable for about an hour drove car light came back on ran diagnostics and code 26 pops up. Disconnected positive cable no results code and light still there. Unplugged ecm fuse car wouldn’t start as usual and died when pulling in parking spot. I can only assume it was relearning. Drove car next day on freeway got gas again and went to destination and as soon as I put car in park service engine soon light came on again. Turned off car and started again twice didn’t come back on the following day I goofed around with hoses under air cleaner box drove car and stopped at several locations and light never came on again. I guess my question is what is the likely problem with this code it’* the quad driver module code? Seems it controls several things so does the unit go bad or things it controls have issues generally? Thank

One of our gearhead members may also have some input to help re code #26. Further diagnostic testing may be possible.
Old wiring? It very well could be an electrical issue. Check the Temp sensor connector & wiring along with the TCC solenoid wiring.
We have a thread here regarding code 26: See post #3 member Willwren knew these cars well.https://www.gmforum.com/1992-1999-91...ircuit-207093/
Also this site talks about #26: https://www.fixya.com/cars/t3298479-code_26_mean

Ya I dinked around with the plugs and looked at wiring and lines running under air box light didn’t come on all day yesterday drove on freeway about 65 miles no issues. Car runs pretty good. About 174,000 and it’* a clean well maintained car lots new.

Sounds like a nice car & hopefully the light stays off for you. I can't stand engine lights on either !

Ya that’* how it seems my problem started both times after fill up. Gas cap was right at point before click I tightened light kept coming on pulled cap all the way off and put back on. Note cap is nearly brand new. I got gas second time it came on when I put in park and the. It didn’t come on all day and I drove city freeway city making stops and everything. So maybe I cured it knock on wood we will see. It was code 26 from what I could tell! What would gas cap pull up?

Make sure you turn the car off during the fill or you'll set the code.

https://www.troublecodes.net/gm/91_38c/
Not sure if this helps, but I really hate this one, because it'* anyone'* guess how to work through it.

Did find this tidbit on a newer era:
https://www.troublecodes.net/gm/92-93-3-8l-vin-l/