Leaderboard

What's best, I don't know, but my personal experience is with Stabil, which I have used since '93 in my Reatta. Never any issue with starting after hibernation. Full tank, drive a few miles to circulate and park it in a storage unit until spring. Remove battery and bring home, give it a baking soda bath and do a maintenance charge every thirty days or so. Worked for me for a long time.

Note the controls are the two Grounds, A & B applied through the engine control module as a function of the engine coolant sensor and the AC. BTW for years you could just download the service manuals and other things from a website with GM's permission. Then they revoked the permission and we got lawyer demands for removal.

What are the TPS (ED01) & IAC (ED22) commands doing ?

Below is the wiring diagram that is in the section of the FSM relevant to your cooling fans. I doubt you have a wiring problem but you might have a bad connection. If the fans will run on high by grounding the relay, it would seem the ECM isn't commanding them to come on high when the engine reaches 230*. The question is why. The first thing you should do is as Padgett suggested. Go into the onboard diagnostics (no scanner needed) and look at ED04 to see what temperature the ECM is seeing when the engine is over 230* on the gauge and the fans should be running on high. Then go to see if you can manually turn the fans on using Overrides ES09 and ES10. Instructions on how to do this can be found in the "Diagnostics" menu at the top of the page.