check hybrid system warning

After getting this warning I discovered the hybrid battery cooling fan was loaded with dog hair on the front side and there was a rodent nest filling up the backside. After cleaning everything out I disconnected the 12v battery and reconnected to reset. The warning disappeared for several weeks but is now back on. My question is.... does this fan run all the time while the car is on or is it intermittent as required, because when I turn the car on I cannot hear the fan running. If I pull the fan out and connect to 12v. and it runs can I assume all is okay or are there other factors to consider? Thanks!