What is my Prius C doing when I am away?

I was taking the trash out late this evening. as I was pasing my Prius I heard a sound of a motor running? Not the motor but comming from under the car say the rear seat area, it sounded like a fuel pump running? The car has been parked for hours. What the heck is going on? I got in and all was off. I started it and then turned it off. Walked to the rear and all was quiet. I don't get it. Can anyone tell me what was going on? I am getting used to all the vaccuum releases that go off moments after shut down. But this is hours and way disturbing.... HELP PLEASE.

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Consensus seems to be: "It is the sound of a pump performing a fuel evaporation leakage check."

I think it has something to do with the Twilight Zone.

It is an evaporation cycle, definitely. It is a prius family standard behaviour, don't worry.

there is a few things that happen. it has a KEY off EVAP system leak check that it will run during specific parameters when vehicle is "cold" also about 5 hours after shutoff it will make the same whirring motor sound you may have noticed about 30 seconds after the car is locked. it has a coolant storage tank that acts like a "thermos" that keeps about 3/4 a gallon of piping hot coolant for the next drive cycle to keep emissions low. at that 5 hour mark it runs a self check and will turn on the pump for a short period of time and then go back off. hope this helps

I'm thinking of buying a Prius c in the near future and this is good to know so I don't have a moment of worry if I hear those sounds.

The C does not have a coolant storage tank to check.

Well that is better then what our smart car does when it starts. It cycles a preheated for the cat. Convt. And it sounds like my wife is blow drying her hair as we back out of the garage.

I kind of like that sound from my smartcar!!

What color is your Smart? Our is black w/ silver tridon cell. Not by choice just a good deal.

Blue metallic/black. I ordered it Nov 07, picked it up 9 months later.

Twice now I have experienced the same issue, it sounds like something electric is running several hours after I have shut off my C. Any one from Toyota monitoring this site who can give us an answer?

http://www.toyota.com/t3Portal/document/om/OM52B58U/pdf/Forward.pdf

I walked outside once and heard the ICE running, keys were inside the house about 30 feet away.
I still don't know what the hell happened? I joked with the wife telling her it had become self aware.
Anyone else had this happen to them?

The ICE should never run once you have powered down the car.

Maybe it wasnt the ICE and isntead it was the same thing the OP heard. I could have swore it sounded like an ICE.

I believe your C like mine is communicating with the.........mothership..... mine really makes noise on winter nights with a full moon, I am just saying, kinda spooky..

I think it would be easy to confuse them. Fortunately I had already read about the evap check here so when I went to the garage a few nights ago and heard the car "running" I did a quick mental check, realized it was about 5 hours since I'd driven the car, so I understood what I was hearing. I might have guessed it was the ICE otherwise.

This just occurred while I was in my garage. It lasted for about 10 minutes and then stopped. Sure enough, it started right about 5 hours since I turned the car off.

My wife told me the C was making noises from the rear trunk and yep, it was about five hours after I had parked it in the garage. I went to the garage to hear the sound but it was no longer present.

I guess that was the evaporation cycle in process.
I think I'm going try to catch it myself.