Wierd sound coming from underneath rear after parked in garage for six hours

No idea really - did you have your smart key in your pocket? And was the car locked?

If I have the key in my pocket and walk past the car - if it's at night, I can see the interior light turn on. My hearing isn't real good - so I'm not sure about noise - but it sure knows I am there.

 

it's an evap check for pollution control. weirded me out the first time i heard it. can you say 'christine'?

 

how long did it go for? Your fuel tank is different from ours here. Ours doesn't have the pressure lock or whatever it's called.

 

right? not sure what the delay is for, maybe it's some kind of leak down test.

 

same here, you have to time it right. i've only heard it a few times in almost 5 years.

 

See: Hybrid battery humming, hours after car is turned off, normal??? | PriusChat

 

It needs beer.

 

It was humming because it had forgotten the words

 

Mine 2019 does this nearly daily. It's doing it now and has been going for hours. Worried that it's going to drain the 12v battery....unless it runs on the main traction battery?

 

I'm sorry I don't have the 2019 Repair Manual handy. This is the timing chart of the evap self test from Gen 3. Adding up the times along the bottom shows the whole test is done in 23 minutes 10 seconds tops, with the leak detection pump running most of that time (all but the first minute). It's a small pump and runs on the 12 volt system and Prii have been doing it for years without issues.

Again, I'm looking in a Gen 3 manual, so it's possible they changed something for Gen 4, but "hours" definitely doesn't sound right.

 

The manual also states this though:
"Approximately five hours after the hybrid system is turned off, you may hear sound coming from under the vehicle for several minutes."

 

I suspect if your Prius detects your smart key when you walk close by, and reacts accordingly by turning the interior lights on, it will automatically begin to prime the vehicle “for lift off” so to speak.

Even my old 2008 Gen 2 without the smart key (UK) will initiate a pre-startup sequence (charging the brake master cylinder I think), as soon as I open the drivers door.

I think this is perfectly normal and every version of Prius does something like this.

Whenever I’ve got home from my commute, parked, got my stuff out of the trunk and I’m walking to the house, my Gen 2 proceeds to make a series of distinctly peculiar noises somewhat akin to the Millennium Falcon venting plasma after it has landed, and the crew are walking away.

I look back half expecting it to be venting gasses like that fictional YT-1300 Freighter. The noises never fail to mildly amuse me though .

Your Prius is perfectly fine, and doing exactly what it’s been programmed to do…..


Source: iPhone 12 Pro Max 512GB ? Pro

 

Evap. system(charcoal canister and related parts that capture fumes from fuel tank) doing a test. I noticed its even mentioned in my manual