Originally Posted by JohnF
There appears to be two fans in this 2011 GMC Sierra. Can I assume one is for the radiator and the other for the transmission cooler as you are describing?
Typically the second fan is for when the a/c is on. When you turn on the a/c it should automatically engage one of the fans to keep some air movement through the condensor. It likely is on a mutlifunction circuit which would allow it to turn on under other circumstances as well. They could both possibly turn on with the a/c as well. There are many variations in which manufacturers utilze dual fans and their purposes for activating.