[Solved] Mysterious Grinding Noise when Car Off for Hours

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.

 

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.

 

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.

 

they must have changed the evap check pump, mine is more of a fan noise.

 

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.

 

Was try to post the same question, searched and found this post.

 

it's not nimh, it's lithium