what is this sound?

I wasn't sure what the sound is but my gen 2 also makes it, I've only ever noticed it when the car is off. I remember something about sounds from the manual, just glanced over it again and in section 2-1 Driving Proedures it does describe a sound that should happen 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 because
the fuel evaporation leakage check is performed. It does not indicate a malfunction. ​

But ... our sound isn't lasting for several minutes so I wasn't convinced that's the explanation. I checked around though and this thread suggests that it is the explanation: Whirring buzzing noise when car is off, in garage hours after shutdown | PriusChat

I'm sure one of the pros will turn up soon and confirm/deny if that sound is the fuel evaporation leakage check, and if it's normal to get it that often. Cool username btw.

 

The two obvious choices (as you all have Gen 2s) are the brake accumulator pump, and the coolant control valve on the thermos. The recording sounds a lot like the brake pump to me, but you should really just grab a mechanic's stethoscope (or even just a long stick with one end pressed to your ear), and press the far end to the brake pump once when the noise is happening, and again to the thermos valve when the noise is happening. Then you'll know.

Needless to say, it's possible the three of you will get different answers.

 

check the 12v health

 

bisco thank you, OK 12V health on mine, I measured it the other day using the gen 2's maintenance mode. seemed good. 12.2V
acc on 11.5V
car running 14.0V
interested in DyingBattery's result.

Chapman sounds good (intentional pun), DyingBattery because yours is making it so often and mine so infrequently, it'll probably be way easier for you to confirm it that way.

 

Haven’t heard that from any reputable source.

 

No, NOT Good.

ACC reading is pretty useless; too little of a load to have a meaningful measurement of battery health.
When done properly, I would not be surprised if the SOC (State of Charge) is no higher than 11V; definitely not good.

READ post #5 & #8, to apply a more meaningful load.
Is my inverter coolant pump slowly failing? | PriusChat

 

OK cool thank you, and incidentally i recall seeing a bunch of very informative posts from you exstudent so I'll definitely take your advice and do it as you described #5! cheers.
It is winter here in NZ, 7:45pm. I will test it in the morning with your protocol. I have got a 12V battery charger. It'll probably be about 8°C.

 

I was here having my dinner and I remembered what happened with my Toyota Camry - some kind individual that owned it before me installed the wrong 12v battery. One day I was stranded.
I thought I'd better check what I've got; just went and had a look and the model # of battery installed is NS60MFHP, apparently suits some Toyotas but not the Prius.
Apparently the right battery is S46B24R.

Could any kind soul please confirm/deny if I've got those facts right? If yes I guess I'd better swap it for the right one ASAP
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edit: I want to mention my Prius doesn't have the smart key. I just did some looking around here and found part number 28800-21181. That led me to S34B20R, I found a YUASA one but it is 28AH and apparently it should be 35.

 

NS60MFHP is a model number, so that'll be specific to one brand.

S34B20R and S46B24R are size references, so potentially any brand could be advertised in those sizes.

I am aware that Priuseses without the smart key system use lower-capacity batteries than those that are equipped with SKS.

In the USA it is getting easier to find the larger S46 battery in various stores; the smaller S34 battery is rare enough that we pretty much have to go to Toyota to get them. Battery manufacturing is very regional due to shipping constraints so I have no idea what you'll find there.

 

OK thanks for sharing your knowledge. i will try toyota nz for the battery because I can't seem to find S34 batteries at 35ah, just 28ah. I can't even find an S46 at 45ah! also i saw that if I did get the S46 I have to get some brackets.

 

That’s correct. All you have to do is replace the Battery tray with part # 74440-47020. That’s the tray for the bigger battery. It’s 21.26 list or practically free at a junkyard. The bigger battery is both cheaper and more powerful.

 

In the USA, it is easier and cheaper to get the 45Amp Hr battery. Even buying the battery clamp for the larger "smart key" battery, it was still cheaper than the stock non-Smart key battery (35Amp hr).
12V Battery Upgrade: non-Smart Key (35A h) to Smart Key (45A h) | PriusChat

Maybe you can get the smart key battery clamp from a junk yard or off eBay?

Bosch, Exide, AC/Delco make Prius specific AGM battery.

 

OK guys how's this for a story?
First up I followed exstudent's method & got 11.1V. According to that SOC chart it's knackered.
Second I rang my local Toyota dealer and asked for a price on the battery, $354+GST. I asked if it was 35 AH and he said he didn't know, he said it was an aftermarket century battery. He said the genuine one from Toyota NZ would be $483+GST. I asked him if he had a model # for the Century battery so I can check the amp hours because I want to end up with a 35 AH battery ... the phone went dead he hung up on me!
Unreal.

 

Didn’t know you were in New Zealand when I quoted that part price. Good luck.

 

According to Centruybatteries, S46B24R is the correct 45Amp Hr (325 CCA) AGM battery for the Gen 2 Prius.

Remember, you have to replace the smaller non-Smart Key battery tray for the larger smart key battery tray to fit the larger smart key battery into a non-smart key car.

Repco seems to have an assortment of 12V AGM batteries that may or may NOT fit the Prius.

SuperCheapAuto carries Optima; I'd stay away from those if you can.
SuperCheapAuo carries the Century you need, $325NZ.

It appears that Yuasa or Centruy are the same battery. Different ID, but same barcode. Post type likely the same although Century lists JIS and Yuasa lists SP (Small Terminal Post; likely JIS).
Overview Details
Product ID: 601130
Barcode: 9415951005263
Brand: Century
Series: Hybrid Auxiliary (Car & Passenger Vehicle)
Warranty: 18months

Product ID: 601227
Barcode: 9415951005263
Brand: Yuasa
Series: Hybrid Auxiliary (Car & Passenger Vehicle)
Warranty: 18months

If your charger is NOT the newer Smart AGM compatible charger, it will never fully recharge any 12V AGM Battery. Why? AGM's have a higher resting voltage (13V). In order to recharge and AGM, the AGM battery has to see a higher voltage to get recharged, say 14V. A non AGM battery has a lower resting voltage (12V) and a lower recharge voltage of say 13V.

 

Just keep in mind the UYODS principle (use your own stethoscope). If DyingBattery uses a stethoscope and finds the sound in that car is coming from the brake pump, that doesn't necessarily tell you what your stethoscope will tell you about where it's coming from in your car. The pump and the coolant valve can sound sort of similar (they're not identical really, but it's hard enough describing sounds in prose on a forum, and recordings can sound different to some people and similar to others, if they're listening for different aspects of the sound). UYODS.

The good news is, neither one sounds anything like a 12 volt battery. (But I'll agree, if you ever catch a 12 volt battery making a sound like that, you should replace it, then use it in a roadside attraction and sell tickets.) Maybe the theory is that a bad battery causes brake fluid to quantum-tunnel out of the accumulator, so the pump has to run to put it back.

Think of it this way. A Prius brake system sometimes has gas bubbles in it after some years, even if it was never opened and no air was let in. The gas is nitrogen used at the factory to pressurize the accumulator, which is supposed to be sealed and impermeable. But any nitrogen that slowly escapes the accumulator into the fluid side over time will form bubbles in there. They can be bled out, using the normal procedure, just like you would bleed out air bubbles after having the system open.

There's nothing extra magic about a fluid 'flush' for that issue, but in doing it you do bleed the brakes.

When the system is properly bled, nothing in the lines but fluid, and you apply the brakes, only a tiny amount of fluid from the accumulator is used, enough to push each of four pistons by about 0.3 mm. When you release the pedal, the pistons return, and that small amount of fluid returns to the reservoir. So with every use of the brakes, a small amount of fluid leaves the accumulator, then ends up in the reservoir. After that happens enough times to reach the accumulator low pressure setting, the pump comes on and stuffs fluid from the reservoir back into the accumulator.

Now take the same picture with gas bubbles in the lines. You apply the brake pedal, and fluid flows out from the accumulator into the lines. More fluid this time, because it has to be enough to compress the gas bubbles to reach the target fluid pressure. You might even hear a whooshy squirty sound as you apply the brakes.

When you release the pedal, those bubbles expand again, and that larger amount of fluid gets whooshed and squirted back into the reservoir. So each use of the brakes, with bubbles present, means more fluid used from the accumulator and returned to the reservoir, means fewer uses of the brakes before the pump has to run again, means hearing the pump more often.

If that's all that's going on, and the accumulator is only slowly leaking nitrogen and not flat busted, getting the bubbles out will help with that.

It won't return to "like-new" condition, because you're not putting the nitrogen back into the accumulator where it belongs, so there's still a reduced gas volume there, which also contributes to more frequent pump cycling. But you'll at least correct one of the reasons for the frequent cycling, and that will keep the cycling down, and maybe keep the accumulator from completely wearing out for somewhat longer.

 

First thing I gotta say exstudent is thanks so much for taking the time to figure that out for me. I really, really appreciate it. I'm trying to get better at working on cars, I'm way better than I was a year ago but me compared to you (or me to any of the major posters in this thread) ... it's like comparing an insect to a lion.

Turns out my charger is for lead-acid batteries - cheers for mentioning that I would've been going nowhere. I'll see if my dad has an AGM charger he's got heaps of gear. if I need to get one I will go with one of your recommendations exstudent. big thanks again! I will go with SuperCheapAuto's Century & the necessary tray.
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Chapman that (UYODS) is such a good point about checking it for myself, and quite frankly I'm disgusted in myself for going on the assumption that my noise was his noise, just lazy of me. I read your explanation as well & I'm staying tuned for more talk about the brake fluid, reservoir & accumulator.