[StorminNorman]

Originally Posted by racecougar

That really depends on what fan arrangement you're running, how you have it wired, and how you're controlling it in the PCM.

In my case, I'm running a two-speed fan. I use pin 42 from the blue connector to trigger the low speed fan relay. I attempted to use pin 33 from the red connector to trigger the high speed fan relay, but that signal kicks on and off rapidly when the coolant temp reaches/exceeds the "ON" temp in the tune file. The low speed works perfectly, turning on and off at the temps I've set in the tune file. I've since ditched the pin 33 output to the high speed relay and instead control that relay via a switch, though I've yet to actually need to use it.

That's what happens when the tuner doesn't "repurpose" the pin in software to control a rad fan, From controlling HVAC door.