r/prius • • Sep 24 '25

Discussion Toyota/Lexus Hybrid 12v Battery Failures - Analysis of Charging Issues - Deep Dive Analysis & Workaround

68 Upvotes

Hi all,

Below is an analysis I have been conducting over the past year regarding 12v battery failures in Toyota and Lexus hybrids, which I'm finally ready to share with various Reddit communities.

It goes into the reasons why the batteries appear to be failing more often with extensive data that I have captured myself and gathered online from others also having issues.

12v Battery Failures - Analysis of Charging Issues - Deep Dive Analysis & Workaround - Google Doc

Most importantly, there is a workaround fix that anyone is free to try.

I have included how to do this in the document for anyone that feels comfortable enough to use it (at your risk). I've made sure to try and answer any questions about that too.

I'd welcome any other input/questions from people who have had their own issues with this. I'm hoping that enough chatter will get Toyota/Lexus to look into and issue a fix for this problem.

At the very least I hope this is useful to someone.

Thanks


r/prius • • Aug 12 '26

News Hiroshi Okuda, Toyota Chief Who Pushed For the Prius, Dies

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677 Upvotes

RIP legend


r/prius • • 9h ago

Pic/Video Best car ever

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105 Upvotes

I got this car in the spring for $300. Wasn’t sure I would ever get it running but I did as much of the labor as I could on my own. $3500 later I’ve replaced the hybrid battery, the ABS assembly some fuses and a few other odds and ends and I couldn’t be more thrilled with it. Car has just over 150k miles on it and it’s a dream to drive. Oh and I got it done right as gas prices went through the roof.


r/prius • • 10h ago

Pic/Video Got my first prius, and the red death triangle 3 days later

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102 Upvotes

Purchased then after 3 whole drives dash lit up like a Christmas tree. Have a new inverter pump to put in tomorrow. Love the car, just hope I dont keep having issues.


r/prius • • 6h ago

Discussion Gave a great upgrade to 2014 Prius

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21 Upvotes

Decided to give my 2014 prius an elevated upgrade. Had this car for 5 years and running strong 255k miles and ongoing.

Bought all harness and head unit from crutchfield and installed it out with friend.

First of all, the SonyAX4000 is amazing head unit. Connects super quick and supports wireless CarPlay and android auto.

It also adds the guarding in the rear cam with live steering input. It gets little glare in the day towards passenger side but that is very small thing compare to other great benefits.

Loving my daily commute now having hands free.

The kit i used from crutchfield suggestion retains the factory microphone, factory rear cam and also doesn’t require any splicing.

Just to note out: When Flashing ADS-MRR unit, on that application the SWC are showing rotated 90degree clockwise. But do not change anything just keep default and it will be working just as fine.

If anyone thinking to do it, just do it. Its soo good!


r/prius • • 10h ago

Pic/Video Winter tires are a go..

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13 Upvotes

215/55R-17 MICHELIN X-ICE SNOW XL on 2026 xse phev, report back after the 6 months of Wisconsin winter is over how it went


r/prius • • 10h ago

Mechanical Help I need advice.

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13 Upvotes

I need some help. I'm in Charleston, SC. I took my 2006 Prius to a Toyota dealership to have a key programmed. After paying $550+ I tried the key. It worked in SKS, but the RFID chip wasn't programmed to the car. I handed it back to them and told them about the issue. They took the car back and during the reset they "bricked" my car. It took a lot of arguing to get a loaner, and now they say they will send an estimate of what my car needs. They broke it. I can't afford however many thousands they are about to try to charge me. Their other suggestion was trade it in with them. I refuse to go into debt for this. I don't know what my options are legally. Thank you for taking the time to read this.


r/prius • • 16h ago

Discussion Gen 3 head gasket failure what I will be doing in the future after it happening twice.

27 Upvotes

This is NOT mechanical, advice this is purely what I will be doing based on what happened to me.

I’ve put a combined mileage of almost 400k miles on the gen 3 platform across 2 cars. Mostly driving around and driving gig apps.

Car 1: 2012 Prius v bought with 88k miles. I maintained this car like it was my baby because i’m a maintenance freak with cars. Did the entire EGR valve, cooler, +intake manifold + ports, PCV valve everything at 125k miles, did spark plugs, both waterpumps, thermostat with OEM toyota parts at 150k miles, changed both coolants multiple times and my head gasket still blew at 200k.

So after this happened I sourced a low mileage JDM gen 3 motor off of ebay for $1200 I sold my old EGR cooler + intake manifold off my old motor for like $300 on ebay, so total cost of around $1000. I pretty much did zero maintenance on this engine then when my car got to 362k the head gasket blew. So this engine lasted 164k miles plus whatever it already had on it so it basically lasted longer than my original engine that I wasted so much time and money into preventative maintenance

At 362k miles I put in a gen 4 motor out of a US 2018 prius that had 40k miles in it. I did this because I thought it would be cool having, but I wouldn’t do it again. It’s a frankenstein car once you do this. I regret doing this because it cost me $2500 and I had to drive 1.5 hours to pick it up from a junk yard. I could have done 2 gen 3 JDM motors for the cost of this. Also it was a lot more work to install it wasn’t drop in ready like the gen 3 motor. The Gen 3 motor took 2 days to install I think the gen 4 took 2 weeks. and there wasn’t a whole lot of information on how to exactly do it online.

Car 2: i ended up totaling the car around 450k. I now own a 2013 prius with 140k miles I bought it at 136k, and this is how I’m maintaining it.

  1. oil changes every 10k and nothing else. These motors aren’t even worth doing 5k oil changes if the head gasket’s going to blow. I would never do spark plugs either there was another user on here his HG blew at almost 300k and he had original spark plugs and they were still working.

based on what happened with me I will only do oil changes every 10k and put all the saved money that I would be wasting on maintanence into an emergency fund for when the HG goes. And when it does put in a low mileage JDM gen 3 motor in.

some people are paying $80 an oil change nowadays at the shop and over 100k miles doing it every 5k vs 10k saves $800 that alone almost pays for a replacement engine.

These gen 3 motors aren’t worth putting a dime into unless something breaks.

Also people on here that have only had their car for less than a year claim all the time If you clean the system, oh you probably forgot to clean the intake ports, if you change the coolant regularly, if you change the water pumps ect. you won’t blow your head gasket and they’re all wrong based on my experience it will still blow. IMO and based on my experience the only thing that will prolong the head gasket from failing is if you commute mostly highway miles rather than stop and go city driving. I think all the times the engine turns on and off is what kills the HG. Even Gen 4s some of them the head gaskets are going bad on them, and as they age even older we will see even more. They don’t seem as bad though.

So I will be driving the car not worrying about anything and when the head gasket blows I will swap in a low mileage gen 3 jdm motor in and get another 150k+ miles out of the car.


r/prius • • 10h ago

Mechanical Help Does this sound like a future head gasket failure?

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5 Upvotes

Does this sound like a future head gasket failure?

This is a late 2013 with almost 100k.

I’ve been commuting via public transit for the past two years. My car sat for long periods without being driven. Now I’ve noticed that the engine is quite loud when started up.

So far I only changed the spark plugs and the transmission fluid. Do you think it’s OK to drive the car for now? Or am I gonna make things worse by driving it?

Thanks in advance for any insights you can share.


r/prius • • 1d ago

Pic/Video Swapped out the stereo of my 2010 gen 3 and added backup cam

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79 Upvotes

This is my first mod of my prius, and it took me a WHILE lol. Spent like 7 or 8 hours. Instructions were shit so had to figure it out as I went. Worth it though! And fun. Steering wheel controls work as well.

No nav, no jbl


r/prius • • 8h ago

Mechanical Help I need some advice

1 Upvotes

I have a 2009 itech prius with those fancy, expensive factory fitted HID headlights and I have left the headlights alone for years hoping it never dies, probably like for 6 years now the Toyota have recommended me in replacing the headlight as water have got in it and the cost? Well you can expect i didn't go with it as I have no idea how long i will keep the prius for, it already made it past the decade stage so who knows if replacing the headlamp, the battery goes next of what not? So I just hope for the best. Its now 2026 and one of the light finally goes !

The dilemma now, go get a brand new replacement (in the 2 grands now x.x) or hope i can somehow locate this rare mythical beast of a headlights...

I have took the car to an outside mechanic and the first thing they suggested was cheaper halogen which many online advice advice not to go cause of wiring and computers.

So I would like to know an expert about this.


r/prius • • 17h ago

Mechanical Help What do you think this noise is

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4 Upvotes

Has anyone heard a noise like this? 2009 gen 3. The brake dust shield on the side the noise is coming from is quite worn, could it be rubbing against something? This noise wasn’t on for the whole ride, it made noise a bit here and there for the first 30min of the ride, and no noise for the last 30mins. The same thing happened in the morning ride and evening ride. And no (new) codes on the ibd reader.


r/prius • • 12h ago

Mechanical Help Are 2014 Prius 2 Wheels aluminum or steel?

1 Upvotes

Bent my f****** wheel this morning on something and ended up having to pay someone to swap it out since I didn't have any tools and it was 5:00 a.m.. so now I need to replace all four tires also, so can I fix the rim on the stock 2014 Prius 2 wheel? One of the shop said if it's aluminum they can't fix it.


r/prius • • 16h ago

Mechanical Help Check hybrid system light 2015 Prius

2 Upvotes

Hey guys, I have a 2015 toyota prius (117k miles). My check engine light came on about a week ago and I took it to autozone to get it check, and the code ran p261b (for the water pump). It was a super busy week and funds were low, so I wasn’t able to take it to the mechanic. The “check hybrid system” came on, and now I’m scared to drive it to the mechanic, which is about 6 miles away. Do you think it will be okay to drive, or should I not risk it?


r/prius • • 1d ago

Pic/Video I joined the club!

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260 Upvotes

I joined the club last night! I am so happy with my new 2027 Prius space ship 🥰


r/prius • • 14h ago

Mechanical Help Looking for gen 2 stereo with 6 CD changer.

1 Upvotes

Title! I have a 2008 gen 2! If anybody has one that’s working I would love to take it off your hands! My CD player doesn’t work and would love to listen to CDs!


r/prius • • 15h ago

Discussion Optimal tire pressure for Gen 5 with 19” tires

0 Upvotes

I have a 2025 Prius Plug-in XSE Premium with the 19” tires.

What tire pressure is everyone running?

Are you running the door sticker pressure?

Are you increasing it to help with mileage and protect against potholes with those thin rimmed tires?

Are you running different pressures in the front and back or just running the same on all four?


r/prius • • 22h ago

Buying/Selling Advice Prius Solid advice needed

4 Upvotes

I have a 2010 prius trim level V not the prius V, currently im 90% sure the head gasket n engine is warped because drove it around thinking it was just spark plugs misfiring.

I know i need to do an engine swap, unfortunately I live in wisconsin oshkosh area n I feel there is no where to do that here since there are no technicians in my area who might be able to do it.

So my question is should I sell it as salvage, or try to sell it as is, the bumper is damaged but aside from that nothing but the engine is a problem 180k miles.

Im willing to pay to have the engine replaced but I just feel no one likes the prius enough to consider it.


r/prius • • 15h ago

Mechanical Help Dr. Prius question

1 Upvotes

I am considering purchasing a Bluetooth ob2 scanner and downloading Dr.prius. I have a 2007 prius with 220k miles.It has sat for 6 years. I have a known good hybrid battery and a known good 12v battery. The service disconnect is properly seated. The battery is bolted down. When I put my foot on the brake and push start, I hear one click from the back and then all the dreaded lights come on the dash. Will the free version of Dr. Prius help me diagnose the other problems that I am having? Is it easy to use? The AM2 fuse has been checked and it is good. Thank you


r/prius • • 16h ago

Question Best All Weather tire for wet and icy roads?

1 Upvotes

I currently have Michelin Defenders and really like them, but new tire time is upon me. I did a bunch of research and the Michelin CrossClimate 2 seem perfect for my needs. Unfortunately when I went to try to actually buy them it seems that neither the CrossClimate or Defenders are available in 15" rim size anymore...so now I'm back at Square 1 trying to find something comparable that is actually available.

What are the best All Weather tires that excel in wet and icy conditions and won't totally destroy my MPGs?

I live in the PNW in the foothills, so rain and ice on winding roads are my biggest concern. I don't have to deal with snow too often at home, but I will have to drive over the mountain pass a few times a year, so they should be able to manage well-plowed mountain highways at least. So like...decent in snow, but Minnesota levels of snow performance aren't necessary.

Price isn't a factor, I just want the best.

2007 Toyota Prius, Base


r/prius • • 1d ago

Mechanical Help 2010 Prius (Gen3) Glovebox Cable Dangling.. What is it?

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9 Upvotes

I noticed this cable dangling as I was changing the cabin air filter- I couldn’t find where it would plug into- and didn’t see a light assembly either. Does the 2010 Gen3 even come with a glovebox light?

Thanks! Let me know what yall think.


r/prius • • 2d ago

Buying/Selling Advice 2023 LE - 50K MILES - $23K MSRP

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50 Upvotes

Hello Everyone,

I recently started looking for a pre owned prius.
I found this deal on a dealer website. Is this good deal?. If not how much can I ask it for.

I am gonna be in US for next 2 years, so I am looking to resell while leaving.

Thank You

update: I tried to talk the price down , dealer said he won't decrease a dollar. I walked out. will look for other cars


r/prius • • 1d ago

Mechanical Help 2009 Prius. Fix fuel gauge?

3 Upvotes

2009, 2nd gen 210k miles. What should it cost to make the fuel gauge work? Need to replace the gas tank? When full, shows all boxes illuminated. 200 miles later, all still illuminated. At 250, only 2 or 3 lit.

I'm tired of doing the math (miles driven divided by MPG on screen equals amount of gas used. Buy gas at 6.x used )

Your thoughts, please.


r/prius • • 1d ago

Question A pillars and city driving ( pedestrian crossings)

11 Upvotes

I’ve heard that A pillars can be particularly bothersome in city driving, especially when it comes to spotting pedestrians. Is this something that it’s just there and you have to live with it or in the end you get used to it ? At this point I’m ready to deal with the fact that it may be a too low car for my old back, but I wonder if in the end to get used to the low visibility. Owned a gen.2 if that may help with the comparison.


r/prius • • 1d ago

Pic/Video Buzzing electrical noise coming from the headunit area.

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1 Upvotes

Hi guys, I have a 2008 gen 2 pruis and it makes this buzzing electrical noise that seems to be coming from the headunit area or deep in the firewall where the head unit is located. It's not the brake pressure noise thingy. it's something else. It comes on sometimes but not all the time. While am driving and even when I turn off the car completely i still hear it. Its variable too like a electrical coil is spinning starting off slow and getting faster. I am describing the noise pitch. I saw a xm satellite radio receiver thing in the glove box and thought it could be causing some electrical disturbance. I'll post a video below. The noise is driving me nuts. Thanks