EDIT: Problem explained, but will leave this up here for those (like myself) who wouldn't have any idea this might happen. Scroll down a few posts to see the explanation from 2k1Toaster, and the quote about it from the Owners Manual in my later post... While going out to my garage to get a tool just now (9:30pm) I heard what sounded like perhaps a tree-trimmer at a neighbor's house. But as I stuck my head outside to figure out what it might be, I realized it was coming from inside my garage -- and that it was my Prius Prime making the noise while off -- and the car hasn't been used in hours. (Jokes about ghosts aside)... What the heck is going on?! This is the first time I've heard this, and it has me worried about my car. Note: * Car is 1 year old with about 10.5k on it, got serviced by Toyota (incl oil change) in January. * The car was used today only for 5 minutes at 4:15pm simply to go get gas around the corner (that's it) -- and that was over 5 hours ago. Other than that, the car has been in the garage, unused all day. So it's been 5 hours since the car was last used. * Car and charger completely unplugged (no charging going on) * Last charged yesterday morning, used car yesterday afternoon for 80 miles, back in garage by 7:00pm yesterday. Not used at all since, except for above 5 minutes, 5+ hours ago, just to go fill up with gas. But that was 5 hours ago. * Charge state of the traction battery is low (out of EV juice), but I won't charge again until Friday, because I don't need to use the car until Friday night. * The key FOB was NOT on me, it was elsewhere in the house (far enough away where it doesn't register) * The weather is mild SoCal weather this afternoon/evening (60s/70s). * Haven't used the car's A/C or Heat in months. * Sound is hard to describe in words. Volume-wise, it's perhaps the same loudness as the "brake noise" you hear when opening up the driver's side door after a long period of inactivity (but that's a different sound, and only lasts a short time). It's a medium-loud low-grade grinding/humming/whirring sound -- constant in pitch. It also was on for at least 45-60 seconds -- as it was going when I first walked into the garage, going while I stuck my head outside (thinking it was coming from outside), and going while I walked around the car trying to figure out where it was coming from. Only a bit after I crouched down by the rear of the Prime did it stop, but how long it was on before I entered the garage I don't know. * Though I can't be certain (as it stopped shortly after I crouched down), it seemed to be coming more from the rear end (like where the traction battery is) rather than the front end, but again, hard to know for sure because the sound might've just been bouncing off my garage floor, and I was crouched down near the rear of the car listening when it finally stopped. Never had that happen before. What the heck is going on?
A Prius makes lots of sounds while "OFF" because it really isn't ever OFF unless you disconnect the battery. Various pumps check and prime the systems all the time. If you still had your key fob on you, as you walked past and the car registered the key it would start priming the brakes, which makes that kind of sound.
As mentioned above, I didn't have my key FOB on me, it was in a part of the house too far away to register (as I know from experience, when I want to change my charging schedule, I have to go fetch it from where I keep it).
Ok then it was probably the fuel evaporation leakage check. Like I said, a Prius is never OFF and makes a lot of strange noises all the time, even many many hours after you leave it. For example the fuel evaporation leakage check starts approximately five hours after the hybrid system is turned off and you may hear sound coming from under the vehicle for several minutes. It is also listed in the user manual...
I've heard our 3rd gen make noises, hours after shutdown. Can't recall if I had fob on me; probably did. Something to do with fuel vapour system, IIRC? Hah, @2k1Toaster got there first.
That’s a strange one. Never heard of this happening to anyone before. I’ll be watching to see if you or someone else solves this mystery.
Perhaps that's it, then. It's unnerving, because 45-60 secs (if not more, don't know when it started) is a really long time for a constant noise like that to be happening seemingly at random (ie, 5 hours after shutoff). At least the brake noise makes sense (someone opening up the driver's side door implies a high probability of the car starting up soon), but coming out to the garage hours after using the car, and hearing that... hmmm... EDIT: using your suggestion, I just searched the PDF Owner's Manual and found this: "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." That would fit right in there with the timeframe, and length it was on. Problem solved, I guess. But if one doesn't know to expect that (5 hrs afterwards!) it can make someone think their car is having a malfunction. Anyway, thanks!
I am surprised by your statement "Charge of the car is low, but I won't charge again until Friday because I don't need to use the car until Friday night." Do you think that if you charge the car today it will lose a significant amount of charge in the next two or three days? Twice, I have charged my car, checked the state of charge (miles available) with the HUD, and left the country for more than 30 days. Each time the charge was the same when I returned, to the tenth of a mile. However, I did attach a trickle charger to the 12V battery both times as I suspect that it would lose part of its charge over a month of being parked.
no, it won't lose charge. but it is bad for the hybrid battery to leave it fully charged. check your owners manual. when you are not going to be using it, leave it discharged to hv mode.
For sure use a charger on the 12 volt for that amount of idle time. A smart charger will not overcharge, will run through a charge regiment, then fall back to a low power mode, just enough to maintain the battery. It will monitor the battery as it goes. Check your Owner's Manual for recommended max charge rate, it might be up to to 5 amp with 4th gen?
Thanks, I hadn't noticed that. Just found it. It says to keep it at a low rate of charge when the vehicle is undriven for a long period of time. I guess a month qualifies as that.
i know, a little ambiguous, right? i think toyota's goal is to make you think about it, and give themselves the correct legal wording for warranty disclaimer due to reduced capacity.
Really a month at 80% or 40% isn't going to make a huge difference, and that's the "full range" that you the consumer can see. Toyota designed it so that it is really difficult to kill the battery. NiMH does self discharge. This is not a design flaw, not preventable, just a fact. If you charge a NiMH battery, you will lose charge over time. NiMH also doesn't like having too high a charge or too low a charge as various things can happen, but the main thing is they don't like heat. The simplified "don't keep NiMHs charged up" wisdom is actually a "don't keep NiMH's charging because that creates heat". Unlike SLAs and other chemistries a maintainer will kill NiMH. Leaving the car at any level where the engine shuts off automatically (2-bars to 7-bars) is fine. For 30-days it is a non-problem and just being overthought. For 60-days, I'd start it in the middle of the charge range or higher. If possible have a friend start it every 60 days and let it run for a bit just to keep everything happy. Remember that dinosaur burning engines also require this sort of maintenance if not run often. Gaskets and seals can dry out, tires can form deformation spots from not being moved, etc. The battery is just one aspect that likes more routine maintenance. When you start getting to the 6-month to a year ranges, starting at a high SOC closer to 80% if best so that when you come back the car will be in the 40% or lower range. If you started a 1 year storage with 40% you'd be close to zero on your return and that will kill the battery. It also may not be enough to spin up the engine to recharge itself, and now you have a chicken and egg problem.
