Hybrid battery humming, hours after car is turned off, normal???

normal, the car is talking. is anyone listening?

but seriously, it's some kind of emissions check. nothing to worry about. scary the first time you hear it though.

 

Welcome to PriusChat! …as bisco mentioned I don't think there's anything to worry about! My Gen II does the same thing and I just put it down to the fact the car is "…having a quiet think", as I often times do myself, and when I hear my car doing it, I just creep quietly away so as not to disturb it, and let it get on with it!

 

Read your owner's manual! You'll find something like this:

Noise from under vehicle after turning off the hybrid system
Approximately five hours after the hybrid system is turned off, you may hear
sound coming from under the vehicle for several minutes. This is the sound
of a fuel evaporation leakage check and, it does not indicate a malfunction.​

 

Gee I guess that's what you get in a Gen3 to have the fixed gas tank whereas Gen2 we have a flexible gas tank. Kind of strange though, thinking of the rare but several incidents of fire after the car sits a while. Who knew the car scheduled after hours maintenance all by itself.

 

Interesting. I heard the same thing from mine a couple months ago. My wife came in from the garage and told me it was humming. I started it up and then shut it off. No more humming, but I was wondering what caused it. Now I know... sort of.

 

Have you stopped to consider that the reason it is humming is that it doesn't know the words? …just a thought!

 

That HAS to be it............................

 

interesting idea about the fires. gas fumes and spark would do it indeed.

 

The fires reported here have mostly been in the front end of the car, far from the gas tank. I'm sure this system is unrelated. And I don't believe the Prius is unique in doing this; I wouldn't be surprised if it's required in California.

Basically, it pumps air out of the fuel tank, and measures how quickly it leaks back in. If it leaks too quickly, there's a hole somewhere, or a seal isn't sealing, or the gas cap isn't on tight. The result is that evaporated fuel leaks into the atmosphere, which can contribute rather significantly to smog. The whole test cycle takes up to about 18 minutes or so. It runs at either 5, 7, or 9.5 hours after you turn off the car - whichever is the first time where the engine coolant is below 35°C.