Parasitic battery drain?

I agree. I think it’s likely very hard to diagnose, especially if Toyota hasn’t identified the issue yet. I wish my dealership would have started the process earlier so that someone who knows what they are doing can take a close look at it.

I had it towed to the dealership and I am demanding a fix. They can keep it for as long as they want as long as they provide transportation. If they can’t fix it, arbitration or lemon laws will kick in.

 

Drawing from experience, one thing that concerns me (as owner of a prime SE, even if I haven’t been affected so far) is related to the frequency of this issue and Toyota’s internal decision making (which I know nothing about).

With respect to frequency, I don’t know if we’ll ever know how common this is. While this 12V battery issue seems prevalent on this forum, several threads reveal some combination of user error/third party accessories as the root cause. Additionally, the users of this forum (and folks that post about this elsewhere) likely represent an incredibly small number of all 5th gen Prime owners, so there’s certainly sampling bias coming into play too.

I mention frequency first because of my past decision making in addressing software bugs. The bottom line is that is that the decision making on whether to address bugs and/or the amount of resources that are assigned to address the bug is dependent on the frequency + severity of the issue, weighed against the costs of the plausible actions (e.g., time, money, public opinion, etc.)

Granted, I didn’t lead car software projects, but I’d fathom that Toyota’s internal decision making is at least somewhat in the same mold as my past experience.

But yea, I really hope your dealer starts taking your issue more seriously. Having someone advocate for you is incredibly powerful, even at the level of our end user relationship with a Dealer’s service departments.

 

Can you post the video?

 

Later, when I have a better internet connection.

For anyone else following the drama, I’m at the dealership after getting a tow before sunrise. I had to get in the door before 7 AM to jump the line since my car would have already been here over the past weekend if it had failed in their hands on Saturday. The service appointment from Friday is now stretching out indefinitely.

Spoiler: (context)

I had previously handed over a 2023 4Runner TRD Pro () loaner I had for a day early to drive my own car for the weekend, since I didn’t trust that the issue would get the attention it needed, and I knew the battery would die in my driveway since nothing had been addressed with the first two visits. I didn’t need to tie up a loaner if they weren’t ready to take the diagnosis seriously.

They have a Highlander loaner available (push them on this if you have an in-warranty Prius with a similar issue – you deserve a loaner or rental if your car is failing this badly with no abuse).

Now that I am in the paranoid habit of diagnosing anything I am driving, I find a nail in the driver right rear tire of the Highlander loaner before driving off the dealer lot. I offer to just take it and patch it if they compensate, but now I’m waiting for my third loaner in four days. Patching it would have been faster than waiting for yet another loaner, but I don’t make all the decisions here.

Edit: good judgment (and presumably a lack of available loaners) prevails and it’s getting a tire fix.

 

It is my belief that the 12V is undersized and the charging system/process as designed doesn't recharge as quickly as it should on relatively short trips.

Also, it appears to me that owners who are having problems unknowingly drove the car off the dealers lot with a damaged battery (from abuse before their ownership) because many of us with thousands of miles haven't experienced a problem. *Unless I'm missing something where these owner's have had problems after a new battery was installed.

The charging cable, ACC use, and key fob drain issues I believe are real. But a more robust charging system should be able to compensate for this.

 

The only reason I say a software glitch is less likely is because, for the most part, people who have factory only setups complaining of the drain is strange. I'm not a programmer but I've been a giant PC and games etc nerd for my whole life. A lot of issues afaik stem from lack of standardization, but at the very least, on an operating system side for something as closed loop as a car - the number of variables is small on the equipment side.

If there is a bug or compatibility issue, it should be limited to specific parts if they had multiple revisions or sources throughout the pandemic for things like sensors for example. But near everyone should have near the exact same set of parts/softwares/firmwares from an OEM perspective. So issues should be largely reproducible for, at the very least, specific VIN series where parts ABCD were used vs parts ABCF, for example.

Hopefully it is just a fault in some part.

The issue as pointed out is the effort they put towards a fix though. I have no clue how detailed the software logging is and how that can be communicated to their software engineers if it is a firmware/software issue.

But alternatively maybe the problem is easily solved with a different slightly larger battery for example. In which case Toyota would go the easy route I'm sure.

The worst part is the experience of dealers writing it off as mentioned by approximate pseudonym. That's just not okay. At the very least I'd hope dealers would be reporting this up the chain resulting in a good set of reports for investigation.

If there's one thing Toyota is good at its ironing things out over time. If they see an issue crop up enough I'm sure they'll take it seriously. But that does rely on dealers to care. I'm not sure dealers care as much as Toyota manufacturing does when it comes to quality control and upward reporting.

 

Abuse at a dealer is something I’ve looked into, especially since mine was traded from one local dealer to another. The thing is, I test drove it at both dealers so I put 3 soft test drives on it that didn’t leave a ton of room for someone else to mess it up. And dealer prep and lot abuse is another factor, but if it’s the electrical system and not the battery, that may not account for this issue’s severity. The 12v isn’t dead yet – it’s receiving daily extreme draw (could be hundreds of mAh) only when not being driven for the past week. I want it to be dealer abuse because that would have a quicker resolution, but this seems like a systemic issue like the TSB for the charging system that was announced in August 2023 for a handful of owners. This car is a December 2023 build so it almost certainly has the fix for that issue, but it could be a bad part or system failure in that vein.

The car drove perfectly for the first 700+ miles, which also suggests that the dealer lot abuse is slightly less likely to be a symptom in my case. But I can’t rule it out, and I have asked them repeatedly to rule that out as a cause.

The dealer is doing better the third time around with their diagnosis, and they are asking better questions. Toyota corporate is involved as well.

As for the ACC, key fob, and other recommendations, I was already following those from my first drive to today, and I do believe they can contribute to strain on a battery. Again, I wish those were my problems.

 

This has been going on with prime since 2017, and is more likely a use case than anything else

 

If you are suggesting a combination of user error and daily habits, that can’t possibly apply to me.

I assure you my driving is pretty close to normal (800 miles in a month, mix of EV and HV, driven economically most of the time with an occasional push, driven nearly daily but not every single day, medium trips and short trips) but correct for Colorado Front Range climate and altitude which are no sweat for every other Prius driver here. I never over-charge the car (leaving it for days on the charger) and I am treating the car as “by the book” as I can while it is an unknown, new car.

I hope I am not misinterpreting, but my issue being written off as “working as designed” or “edge case” is how this didn’t get addressed by the dealer service center in the first place. They are now probably as puzzled as me by this issue, since this isn’t a common case.

 

I have built gaming PCs for myself and I am my own tech support, so I know exactly what you mean. I agree that modern cars are more of a closed loop and they are often remarkably reliable and robust for what they do.

However, there is always a first failure in a recall or systemic issue. Every time there is a massive automotive software failure that requires a recall, or a crucial safety part that hurts or endangers people, all of those parts often tested “acceptable” until they didn’t.

Fortunately for me, this one is more of a reliability concern than a true safety issue.

 

Going back and rereading your posts, I don’t see any testing with data, so that makes it difficult to understand and help

 

I’ve already spent dozens of hours this past week dealing with researching the problem, managing car dealerships, talking with Toyota, so it would be a bigger project to share more than I have done already, that I am not up for today.

I might be able to pull up some limited data and mileage logs if there is something that would help someone in particular, but I don’t know how helpful that would be, and I don’t need anyone troubleshooting the problem besides people who are hands-on with the car.

We’re all speculating here, I admit, but we are lacking actionable information that I probably can’t provide to anyone’s satisfaction. For me, I am providing only my perspective on a “cautionary tale” of car maintenance, and a recommendation for owners to self-advocate as consumers of finished products. If we also get to the bottom of the technical issue, that’s great, but I don’t have any advice for people besides making sure that the warranty on their expensive car stands for something (otherwise, buy cheap, self-maintain, find a good mechanic, I guess, but none of that applies here).

Also, the dealer has my car in the shop indefinitely, hopefully sooner because I have a loaner, and it’s now their job to collect data. I feel like collecting data and talking to independent experts who are better than me at collecting data is not an effective use of my time with a brand new car that is supposed to be a local driving and road trip machine. I love the car but it isn’t a hobby project for me. I keep detailed maintenance logs (few to speak of in 30 days of ownership) and I’ve put one tank of gas in it. Car worked for 735 miles and then it failed badly. I am not even sure anything can meaningfully be tested on it without access to a known-good battery and the equipment and documentation that Toyota dealers have and I can’t afford. I don’t prefer to leave the car to a dealership but my other options are expensive, inconvenient, and won’t be much more likely to fix the problem. And if they can’t, give me arbitration and a working replacement or my money back. This is what lemon laws and arbitration are for.

 

This.

I’d go further: anyone with a half-decent multimeter, a 10 mm box wrench, and a few test leads and a clamp or two can test this. Normal is around 20 milliamperes. In a nutshell: put the meter in series between neg battery post and car body, measure amperage with car completely off and quiet. With and without charge cable attached.

 

https://we.tl/t-ROl0h0COvy

I’ve got 10+ minutes of this video, but this should do. Later in the process, the headlights quit, but a 12v battery dying on a Prius involves a lot of flashing lights inside and outside of the car, and a ton of interior noise. At one point, the car made a constant tone for 2 minutes straight (I believe it’s the “put on your seatbelt” whine which is appropriately loud and constant).

 

The dealer said they did this and it was within spec. I believe them because they probably don’t want me back for warranty work anymore. It’s in their interest to do the diagnostics they are telling me that they are doing.

I can do that myself, but I’m not wasting money and time on a barely driveable brand new car doing that if it’s supposed to come from the factory with a working battery and electrical system. I am all for the ownership experience and maintaining easy stuff myself, but not on a car that is failing mysteriously. I know it doesn’t sound like it from my posting about warranties and dealers, but I have an oil filter and tools ready to go to self-maintain this car. I can’t even do my first oil change myself and install my own dash cam because the car is no longer reliably driving anywhere.

 

Man, I really feel for you. I can't imagine how frustrating it would be if my new Prime was so flaky and so far, unsolvable. It's certainly not what one would expect of the car.

 

That won't necessarily tell you anything. What you need to be able to do is chart the power draw over periods of at least several hours with and without the cord attached. And without a Toyota keyfob getting close by. You need to see if the cordless car can get to a lower draw than the corded car once they're both in deep sleep. And you also need to check if the corded car is being woken out of sleep more often because of some type of monitoring routine. You have to look at the car like a laptop, not a traditional car that's either off or on.

 

Yeah, I think you're right. Hopefully dealership will sort it.

 

The car is so outstanding otherwise that I would get the same model again, or take this exact car back if they do a major fix. One of the best cars I have driven or would consider driving.

 

Get a battery monitor and watch the battery from your phone to get more information. Not expensive on Amazon.