Inverter cooling fan coming on

Sounds like the battery cooling fan--it has an intake on the right rear passenger side of the vehicle. I wouldn't worry about it. The fan is supposed to cool the battery pack in order to keep it in its most efficient temperature range regardless of outside ambient temperature. The battery will heat up after a lot of driving and will stay warm even over night since the battery has a pretty high thermal mass.

Andrew

 

The Gen2 (2004-2009) wasn't as aggressive in cooling the batteries--as I understand it. I don't actually have a Gen3 so I can't comment further about that, but the cooling system is basically the same (the Gen3 just uses it more).

Andrew

 

All Prius have traction battery cooling fans. While driving my vehicles, I've heard the fan come on, usually in warm weather.

 

My grill is blocked almost 100%. OAT has been in the 60's & 72F over the last couple afternoons. The car sits outside all day & my commute is ~35miles, mostly highway 50-55mph posted (average speed is 30mph). Today the highest coolant temp I saw was 195F. I have yet to hear a fan spin up in either car.

 

I had a candy wrapper flapping around in the fans basket before I cleaned it out and it was loud! The sound of the plastic flapping in there made the fan noticeable. I Certainly could hear the fan at the third level really turning to push air to battety. I kinda miss that wrapper! Let me know it was cooling! The fan runs really quiet. Next time I clean it I may reinsert a plastic wrapper.

 

I've monitored the speed of that fan with a ScanGaugeII, seen it go up to "4" (on a scale of 6?), but have yet to hear it. If yours is loud enough to easily hear, I would look into cleaning it. It's a relatively easy DIY to dig down to it, and you don't need to remove the fan itself to clean.

BTW, if you're searching: it's not the "inverter cooling fan". Inverter is the component next to the engine. You could try "hybrid battery fan", something like that.