Is there an Android app I can use to monitor 12V Auxiliary Battery Temperature on Gen 3 Prius?

Is everybody okay over there things all right? I think the code you're looking for is indicative of a hybrid battery HV battery temperature sensor not the 12 volt I don't think there is a 12 volt battery temperature sensor in this vehicle anyway and most cars there's no reason to monitor the 12 volt battery unless it's hidden somewhere where it can't get air and all that the Prius has a piece of duct work that goes right across the top of the 12 volt battery when the battery fan is on air will blow across through the HV battery through that little leg of ductwork and there's a cut out in the bottom of that ductwork you can't see but you can feel it with your fingers and air will blow right on top of the 12 volt battery it'll be warm air coming through the hybrid battery first but air flow nonetheless. I've never heard of a 12 volt battery overheating in the Prius like even sitting in the sun in the parking lot in 110° weather in Arizona for 8 hours waiting for its human to come out of work. So maybe check that situation out check your code again or something I think maybe there's something going on not in the 12 volt system.

 

Gen 3 does have a temperature sensor above the 12-volt battery. It is attached to the hold-down bracket and sits in the air an inch or so above the battery. So maybe it is more of a battery-surroundings temperature sensor than a battery-itself temperature sensor.

It is called out in the wiring diagram as S17 and the legend says "HV Battery Thermometer" but I think that might be a mistake, 'cause the 12V battery is definitely where it's located. I guess you could say it's in the path of the HV battery "exhaling" air on its way out the quarter-panel vent, but that feels like a stretch.

The diagram shows all the other HV battery thermistors wired to the HV battery smart unit, while this one is the only one whose wires go straight to the power management control ECU. I had always wondered why there was one HV battery thermistor wired differently from the others, but now it starts to make more sense.

So it's possible that any scan tool that shows "HV battery" temperature readings might already be showing this one among those, and if they followed Toyota's weird labeling, it might be shown as an HV battery temperature reading, maybe for "exhaling" air.

You could go dunk it in your coffee one morning and see which reading on the scan tool changes.

 

So then on the Gen 3 like the generation 2 isn't the output duct from the battery fan and battery going across the top of the 12 volt to the little vent in the rear quarter panel on my generation 2 as that piece of duck to work is going right over the battery if you reach under the ductwork you'll feel a whole a cutout and when the fan is on the warm air that's coming from the battery will blow out of that vent right on the top of the positive terminal of the battery you can put your hand there and feel it if you command the fan and put your hand there I'm wondering if that air is triggering I don't know the temp sensor near the 12 volt battery I didn't think that was a good idea personally and in my generation twos all of them I have zip taped that hole in the ductwork closed so now all the air from the hybrid battery is going out the quarter panel vent none is dropping on top of the battery no matter what temperature anything is so the battery is pretty much going to see the air conditioned air in the car as it moves around because I keep it cold in there and so does my HV battery when I put my hand on the output duct that goes out of the quarter panel when I've had a good run with the car the air coming out of that duct work doesn't even feel body temperature which is about 99° so I guess that's reasonably good considering everybody wants to keep the battery is cool as possible apparently I thought some heat was good means things are working and moving it

 

That's that's right I never saw battery temperature for the 12 volts anywhere in those softwares and I don't have the car here now to look and see if it's in the tech software or Toyota software which I have which I did run on the generation 3 many times through an engine change and everything but never noticed or saw or heard anything about 12 volt temperature sensing. Like I said there's a cutout in the vent that will allow the warm air coming out of the HV battery in route to the quarter panel to drop right on top of the battery I mean it's a big old gaping cut out I taped mine up I didn't think that was a good idea unless you live in freezing conditions or something and then you would have to drive like crazy to heat up the HV battery to get some heat on the 12 volt seriously that doesn't sound right

 

Gen 3 has less ductwork back there than the earlier gens. The HV battery exhaling air just comes out from the battery case into the area underneath the deck board. It eventually finds its way out the right quarter panel vent near the 12-volt battery, but it isn't ducted all the way there like the earlier gens.

That is some weird nonsense you found there. I'm not sure if it's that way because some AI wrote it, or just because some mixed-up human wrote it. It's another example of how often it happens somebody goes to sources other than the Toyota repair manual and gets caught up in bogosity.

"Generator control ECU" is bogus. There is an "MG ECU" inside the inverter, but this thermistor is not wired there. It's wired to the power management control ECU, which is behind the glove box.

Toyota Service Information and Where To Find It | PriusChat

 

You get what you pay for.

 

The sensor is indeed mounted above the 12V battery on the hold down bracket. But it doesn't look anything like those pictures on gen 3, and the battery clamp assemblies don't look anything like that on gen 3 either. So the pictures are quite wrong also.

At least you did end up looking in the right place and found the sensor. There'd just have been a lot less bogosity involved by going to the Toyota repair manual right off. It has the right text and the right pictures.

 

You mean no lab white coat answers?

 

Asked and mostly answered in the posts above. There are scan tools that can read all the live data available from a Prius. Because Toyota mislabeled that sensor in the wiring diagram (but not the repair manual) as being an "HV battery" temperature sensor, it is possible that an app you find may display the reading mistakenly as one of the "HV battery" readings. If you dunk that sensor in your coffee some morning and look for which reading on the scan tool goes up, you will know which one it is.

Or, because you already have P0517, it is possible that one of the readings you see on the scan tool already looks implausibly high. If you then go unplug that sensor, and no other reading goes implausibly high with that sensor unplugged, then again you know which one it is.

It's also possible there is no PID for that available in the ECU, in which case there won't be any scan tool that can read it for you. The troubleshooting procedure for P0517 in the repair manual does not mention a live data PID you can consult, and it typically would if there was one. But again, the engineer writing that procedure might have been looking at a list of PIDs where it was mislabeled, and missed it that way. Because of the mislabeling, it's also possible very few people here have ever been motivated to get to the bottom of it, and you might just need to try the approaches above and see which reading it seems to be. You could even report back.

I don't know if that answer is straight enough for you but it may be the best I can do from here.

I suspect rjparker meant how much you pay for answers on PriusChat.