12v battery issue

How did he determine that the traction battery was dead?
If that were the case, you will have a lot more problems than a 12v replacement.
That being said, it could certainly be a weak 12 volt.

 

Hopefully, it’s just a low 12v from sitting for a week

 

More than likely the 12V battery is weak and needs a recharge, since it's getting cold - that doesn't help the battery either. When he's running around the city, are they usually "short-hops". The traction & 12V battery doesn't get recharged, if your only running the car for 10 minutes at at time. Has the dealer/mechanic, checked and topped off the electrolyte levels in the battery over these years? I had to put some distilled water in mine last year. Did he leave the car plugged in for the week he was gone?

 

I believe MEG1 in the transmission is the starter/alternator. If your 12V battery is low, <10.5VDC - funky things happen to electronics. They get "delirious", and trigger all kinds of phantom error codes. Charge up the 12V battery and plug-in the traction battery. Bring them both to full, clear all error codes and go from there. The cars' internal systems are pretty good at protecting itself from damage.
Put a DVM on that aux. battery, while the traction battery is plugged in and charging or the car is in "ready mode" - you should see 13.5-14V. With the car off, and unplugged, battery should read >12VDC.

Hope this helps......

 

You almost never see a Prius with a traction battery that is truly discharged. When you do, there is no way to start it at all, because the traction battery is what starts the engine; you need an appointment with a high-voltage traction battery charger if that ever happens.

The battery charge level display on the dash just covers a normally-used portion of the battery charge range. When that display looks "discharged", it just means the traction battery charge is at the lowest level the car normally likes to use; there is still plenty of charge left for starting the car. (People do get into trouble sometimes if the engine has a problem making it hard to start, and they try a bunch of times; do that enough and you can indeed end up with a truly discharged traction battery, and need a high-voltage charger to save the day.)

There isn't an alternator for the 12 volt system. Whenever the car is READY, the 12 volt system is being supplied by the high-voltage system through the "DC/DC converter" that lowers the voltage, and that's how the 12 volt battery gets charged. Even when the dash shows the traction battery "discharged", this is still what's happening.

So what keeps the traction battery charged? Other than plugging it in (for a Prime), the two motor-generators in the transmission take care of that. Whenever either one of them is generating more than the immediate propulsion needs, the surplus is going into the traction battery. MG2 does that when the car is regeneratively slowing, and the car can arrange for MG1 to do that any other time the engine is running and the traction battery wants charging.

Reports of electronic delirium and "phantom" codes can be greatly exaggerated. Several of the ECUs in the car have specific trouble codes they will set if the supply voltage dips below 9.5; that isn't delirium, they're still non-deliriously doing their job, and part of the job is to set these codes to say "hey, just letting you know voltage got below 9.5 here".

It never hurts to make sure the 12 volt battery is well charged if there's any doubt—the Toyota repair manuals are full of little notes to make sure it's at least 11 volts before working harder on a diagnosis—but it also doesn't hurt to make notes of what codes you do have before just assuming they are "phantom" and clearing them. There will be times they are telling you something worth knowing.

 

Well the good news is that your covered under warranty - EXCEPT for the 12V aux. battery. That's covered under the 3yr/36K mile bumper to bumper warranty - which you've surpassed by 20K miles. NY is a CARB state? If so, traction battery and associated EV electronics are 10yr or 150K mile warranty; otherwise 8yrs or 100K - Your covered either way. I almost guarantee you the dealership will charge you for a new battery and possibly a tow-in diagnostic fee. So worse case, bill shouldn't exceed $700.

Since we're getting so many aux. battery questions. I decided to use my car as an example.
1. I plug-in every night and burn through my 25 mile EV range almost every day, plus 10-15 minutes on ICE to get to my destination.
2. If the ICE is running when I"m parked and reached my destination; I'll let the ECU complete ICE cycle before powering down.
3. I do biannual aux. battery inspections and top-offs, if needed
4. Car is parked outside, so exposed to the small temperature swings in my area.
Last night was in the low 40's with cloud cover, holding in the heat, and the car completed it's recharge cycle. Battery was at 11.5VDC, read on a certified Fluke meter. I placed the battery on a 10A charger. 15-20 minutes and levels came up to 13.75VDC, after another 10 minutes battery voltage settled at 12.65VDC. My battery is behaving normally, didn't disconnect it from the car or do a load test.

Hope this helps someone gauge their aux. battery performance.

 

when the o/p refers to the hybrid battery being discharged, he means that the wall charge is depleted, and it is running as a hev.

there is no 'altenator'. the engine charges the hybrid battery, and the hybrid battery charges the 12v battery. as long as the car is in ready, and also when plugged in.

this is a classic example of when triple a or the like pays off.

 

Both codes are related to the traction pack system.
here is a link for the toyota dtc u019b

and a link for the toyota dtc p0a1f

The 12 volt battery ? possible, With these cars a lot of things are possible.

 

It was discussed that charging the traction battery externally does not charge the 12 volt. I charge my 12 volt at least once a week, did it today. Of course if one has a battery monitor on the battery so much more voltage info is there than a multimeter, and a state of charge value. Plus temp on some.

The reason I charge so much is very little driving time episodes, usually 10 mins sometime 5 mins. The traction has no time to fill the 12 volt like an alternator would. Learned and now adapt to the situation.

The check engine light on at the beginning of the story is surprising on a 2021. Check engine light on but running fine, I don’t know that seems like don’t do that, go to a dealer.

 

it is at the dealer, that's the frightening part

 

No the REALLY frightening part is he is turning to PC Egineers (mis spelling intended) for advice!

 

Most of us here at Priuschat are not engineers, only like minded DIY ers that may understand some of the hoops that need to be jumped through when doing DIY repairs on a Prius.
Of course there are also a LOT of cynics providing their own unique input as well.

 

It’s ironic that people come here to learn or teach, yet criticize those who come here to learn or teach

 

Engineer is not even the top dog class. It’s a wide ranging mish mash of inequality and sometimes self promotion.
He needs to go to a professor of engineering, tenured and published with awards, to get the real low down. Of course, how is he going to do that? Would the professor know about his own 12 volt issues in his ev? Probably not.

 

If they're anything like the demographic studied here:

 

My experience with my 2017 model has been extremely positive. With the local dealer not so much. Mine still has the original 12V battery. I carry a charged 12V jumper box in the car and have a Fluke DVM at home to check the battery. I know I will eventually have to replace it and found that Costco currently doesn't stock it and the local dealer wants $315 for a replacement. This is the same dealer who wants $59. for and engine air filter and $79. for a cabin air filter. I am not an EE, but did retire from the Navy as a Master Chief Electronic Technician, so I do understand a little about the car's electricity and electronics.