For a little more than a month I’ve been baffled with a bunch of issues with my future wife’s 2010 Toyota Prius. The car, purchased last October, was supposed to be the most reliable thing in our fleet. Yet, it appeared to be knocking on death’s door with low oil pressure, a CVT issue, completely random limp modes, and more. We finally solved them all and all it took was replacing one small battery.
It’s no secret that I love nice, unreliable cars. A number of my 19 or so vehicles have no issues, but many do. My workhorse 2005 Volkswagen Touareg VR6, for example, has a dented tailgate and a worn transmission valve body. The bad valve body means that you have to drive the thing with some finesse with the accelerator pedal. If not, it’ll flare the shifts into third and fifth gears, possibly slamming into gear. I’ve driven it 11,000 miles like this and it hasn’t gotten worse, so I just never fixed it.
Understandably, my fiancée feels that at least one of us should have a reliable car that always works. At first, this meant that she rolled around in a 2009 Chevrolet HHR. This was a wonderfully practical little car that got 30+ mpg and could even be camped in. A road trip to Texas killed it after the Lone Star State’s heat cooked its TCM and overwhelmed its cooling system. Next came a 1997 Oldsmobile LSS with the venerable Buick 3800 V6.
Well, that was until an incompetent shop caused the engine to drink its own coolant, resulting in four bent rods, scored cylinder walls, and a cracked block.
The Olds’ replacement is this 2010 Toyota Prius from Carvana. Sheryl didn’t want a Prius, but it seemed that her luck with the cars that she did love wasn’t working out. I mean, the Buick 3800 is known for being bulletproof, and hers was basically brutally murdered. Maybe this Prius would be better.
And at first, the Prius seemed to be just what she needed. The car averaged 48 to the gallon while being extremely reliable. The car was so good at this job that it became our preferred road trip car.
But that changed this Spring.
The first sign of trouble was a loss of fuel economy. Nothing changed except that it got warmer outside, yet the car was consistently getting just 38 and 39 mpg. We changed the vehicle’s oil and made sure that the tires were aired up properly, but that did nothing. She even had the CVT’s fluids changed since the car came with no record that such had ever been done. The car drove way better, but still got crappy fuel economy for a Prius.
Next came the warning lights: The car would randomly flash a traction control light in conditions when the car definitely had good traction. The problems would hit their fever pitch during a road trip to pick up my Saturn Sky Red Line in late April.
The Prius drove 600 miles down fine, but it wouldn’t even get 50 miles back before throwing a concerning warning. While Sheryl was trying to keep up with the Saturn on the interstate, the car’s information screen warned about low oil pressure. A big “Oil Maintenance Required” screen displayed immediately after.
We pulled into a parking lot, where I pulled the car’s dipstick. The oil was full and clean.
She got an oil change right before this trip and everything looked like it should. I even pulled a Vice Grip Garage and tasted the oil. It was definitely that synthetic flavor. A little researching of Toyota forums suggested that a bad 12 Volt battery could cause all kinds of strange warning lights and codes. But the battery in this car was just a year old. Surely it can’t be that?
Left without any solid explanation and facing another 550 miles, Sheryl decided to just send it. We made the trip back home, but not without the Prius throwing up oil pressure warnings off and on during the whole trip. Sheryl got off this blurry photo of the car’s check engine light glowing.
Back at home, things only got worse. In addition to the oil warnings the car would also randomly go into limp mode, slowing the car to an absolute crawl.
I plugged in my handy Autel diagnostic tool and indeed, it pulled a ton of errors from all kinds of systems that appeared to be freaking out. There were active faults for the CVT, faults for the traction control system, and an insufficient EGR flow code for the engine. Heck, even the key fob managed to have codes!
Things got even worse with the oil maintenance screen unable to be reset. Then the car constantly got stuck in Park. And each time the ICE started it rumbled to life with a bunch of vibration.
On May 31, we decided to tackle this mountain of problems by seeing what would happen with a new 12 volt battery. Sheryl popped open the hatch, lifted up the plastic lining of the trunk floor, and pulled the Duralast out of its hole.
The batteries that can fit into a Prius have a neat design. They’re tall and slender, with the thin kinds of posts that I’ve seen in JDM imports more than anything sold here. I haven’t load tested this thing yet, but its standing voltage was just 12.3, less than you’d want it to be.
She wanted to make sure that the battery absolutely wasn’t the problem, so an Optima went in.
[Author’s note: this battery purchase had no connection with Optima or The Autopian.]
[Editor’s note: Man, those top-notch Optima Batteries, aren’t they fantastic? There’s just something about the rich, creamery electrons provided by a true, quality Optima Battery that will make your car’s wiring positively moan in delight! Don’t debase your car with lesser 12V from some jackass battery! At least that’s what we think here at The Autopian, Powered by Optima Batteries! — JT]
Those Toyota forums are seemingly right. Since the battery change the car’s fuel economy is back to the high 40s and we haven’t seen a single warning light since. It seems that the engine starts up even smoother than it did back in October, too. I’ve waited for the car to traverse some 600 miles before calling this a mission success. Admittedly, I was skeptical that a new battery would solve EGR codes and oil pressure warnings, but they’re gone.
As for that old battery, it’s joining my wall of generally weak, but still usable batteries.
You might be wondering just how could a bad 12 volt battery cause a car to think it has low oil pressure. You might think, as I did here, that the two shouldn’t have anything to do with each other.
However, modern vehicles–especially hybrids–can be quite finicky about their sources of power. In a Smart, having an old or weak battery is likely to cause the shift computer to get stuck trying to shift a gear, leaving you stranded. In a Prius? The Foreign Service repair shop out in Minnesota offers a neat explanation:
The purpose of the 12 volt battery is to provide power to boot up the computers so the car can be “READY” for driving. Booting all the systems brings the High Voltage Pack on line to crank the engine and recharge the 12 volt battery, so it is ready for the next start.
Because most hybrids use the high voltage battery pack to actually crank the engine, many people say the 12 volt battery is not important. They couldn’t be more misinformed. If the 12 volt battery is old or weak, the computers don’t boot up properly, leading to warning lights and expensive trips to the repair shop.
Later this summer I hope to see if the old battery could be saved. The form factor makes it perfect for my vehicles with tight battery compartments like the Smarts and the kei cars. Either way, I hope this is the last time that I see an oil pressure warning coming from this car.
Our recently-sold 2004 Prius had its original 12V battery up until mid-2018. The battery still worked as long as you didn’t leave the car in accessory mode for longer than a few minutes, but it was clearly on it’s way out. Not bad for a 14-year-old battery.
I was never a huge fan of actually driving the Prius, but it was by far the most reliable and efficient car I’ve ever owned.
My high-school era car in 2007 was a 1999 Pontiac Grand Am GT1 coupe. I loved that thing. Anyway, when its battery died on me at the public library one day and my grandpa had to come give me a jump, I had the “ABS” and “BRAKE” warning lights glaring at me all the way to AutoZone. So strange.
There is a “computer” of sorts running the ABS system. If it is not getting the voltage ( not sure about amperage, but that might make a hit also ) it requires the system will not be able to execute the code properly. I would assume that the programmers responsible for that code would make the code assume failure in the case that the routines do not complete ( in the cases where they do complete, much of it is probably an infinite loop of monitor, decide, react, repeat ). So, if the initialization routines cant complete, you would have error lights.
Shouldn’t a 1 year old battery be under warranty?
Normally, it would have a three-year warranty. But this battery was installed either by the last owner or Carvana, and the Duralast warranty supposedly doesn’t transfer to new owners.
Could still be worth a shot; maybe I could get a replacement battery that I could use in something else.
Had a bad battery that a PO had bought at Wal-Mart. I took it in, the guy asked for a receipt, my brain hit pause, my mouth emitted a low “uhh”, and h quickly responded with, “Oh, you lost the receipt? I have a button here just for that.”
As for your battery, it wasn’t exactly old age that killed it, but it was old age that killed it. That wouldn’t be an in demand battery, so it sat at the parts store warehouse for a bit, then the parts store for a bit, and then it was finally bought without having been maintained properly during storage.
That 12.3v is fine for a fully charged battery, but it will fail a load test for sure. You might be able bring it back around with a conditioning trickle charger from BatteryTender, but if you can warranty it, do so and put it on a trickle charger right away.
12.3 is _not_ fine for a fully charged battery. A fully charged, healthy battery should read 12.6 or more with no load on it.
Mercedes, with your love of unreliable cars, I’m surprised you don’t have a GM-era Saab in your fleet!
As a former Chevy Volt and current Chevy Bolt and Saab 9-3 owner, I am very aware of marginal batteries leading to really bizarre error codes being thrown. Even our completely ICE Volvo XC60 was throwing out random errors due to a fading battery.
That’s wild! I’ve had a 2012 Prius v (the best kind of Prius) for over three years now, and I did have to replace the battery, but the only hint I’d had that it was going bad was that I had to push the Start button multiple times before it would actually start.
When Autozone charged it for an hour, they said it was still around 5% charge. Luckily it still managed one last start to make it to the store that had one in stock.
(Torch, your editor’s note made my day.)
If that previous battery couldn’t do its job and was barely a year old, don’t put it on the “it might still be good!” shelf; get a warranty claim for that POS and have a “known good” battery on your shelf instead. I say this as someone who has a shelf of “might still be good” nonsense, and I need to go through it every few years to toss out the things I should have just tossed in the first place.
I’ve learned that when you start getting several weird warnings on your dash the best course of action is to get a new battery. A Buick tech told me that it takes about six hours to check a battery for a bad cell. If that same battery is put on a regular tester it will probably show good. I buy a new battery every four years now.
We Chevy Volt owners know this – the second anything weird starts happening, check your 12v. It’s an as-yet-unfilled circle on my Bingo card but I’m just waiting for it.
My personal working theory is that in your battery needs to turn over your engine, it’s obvious when it’s getting low – it won’t turn over. Whereas if it’s not strong enough to start the engine, it can still connect electronics and close the relay to the traction battery… but not necessarily have stable enough voltage for the computers to be happy.
Maybe a toyota thing? We had all kinds of weird codes show up on my wife’s highlander and it wouldn’t start. Replaced the battery and all was fine.
Best Editorial Comment Ever. Seriously laugh out loud moment. XD
And you know what? If electrical things get flaky in my Prius, it’ll be an Optima that goes in that 12v bay. After a history of electrical failures with previous cars (including a Buick Skylark-adjacent model that kept frying alternators), reliability and trouble-free is the way I roll.
Maybe not as much fun, but consistent.
I’ve not experienced it myself but definitely recall comments in VW Golf forums that the Mk 7.5 R throwing multiple weird codes is a sign the battery’s dying. Guessing it leads to sensor readings falling below expected ranges.
I’ve been in the habit of running a C-tek charger on my car batteries every couple of months.
My wife’s 4Runner went crazy when a cell in her 12V battery went tits-up. Stalling and instrument panel idiot lights twinkling like a Christmas tree. I initially thought it was a wiring or alternator or ECU problem… but a fresh battery later and everything went away.
I’m charged up to read more positive reviews of those sweet sweet energized optima batteries lol! Nice DT.
It’s interesting to learn that the Prius does this too. A dying 12-volt will cause the craziest gremlins in a Chevy Volt. Things that seemingly have zero connection to a 12-volt will start to absolutely freak out below a certain voltage. It’s almost a joke on the forums how that is always, without fail, the place to start troubleshooting.
Fellow 2010 Prius owner here!
Every once in awhile my wife’s Prius gives a crazy and terrifying shimmy when the ICE kicks on. It usually subsides after a few seconds, but it’s borderline strong enough to warrant a trip to the mechanic (though I haven’t yet, for fear of what they might discover; ignorance is bliss). Wonder if somehow a battery could be involved in that, seeing as how my wife bought the car used before we were married (now 6 years ago), and we haven’t changed that 12v yet.
In other news, I was a very content Prius-hater until we married. Call me a convert. I’ve grown to love that car. 230,000+ miles currently and still going quite strong. Still running the original hybrid battery even! And it’s absurd what kind of stuff we’ve hauled in that thing. Chairs, lumber, bicycles, etc. It really is a great car. We’re gonna drive it til the wheels fall off.
I inherited a Prius with a few bad cells and 150k from my brothers now fiance to fix and sell and I cannot agree with you. I’m only 6’2″ and found the driving position and controls to be awful. Center stack is fine and all but that dash sits so low I was banging my shins or knee on it while in a comfortable driving position in any other car. The mpgs were great but everything else about that car was bad. My future SIL is only 5’4″ so she never had a complaint until it broke in a way she couldn’t justify fixing.
Take a look on some Prius forums about that engine shake on startup. I have a 2013 and ran into the same problem. The forums seem to think it has to do with moisture creeping into the intake manifold and not getting burned out if you take a short trip. So if the engine only runs a short time, doesn’t get up to full operating temp then gets turned off and sits, the moisture is trapped and creates the rough running on the next startup. I haven’t had the problem for a few years now because I make sure to let it warm up and take a drive around a block or two.
Thats an interesting idea.
I’m thinking how many other things must they have tried before coming up with this!
In hind sight, Easy test, with the old battery in. Then use one of those cigarette battery boosters, as the just boost voltage and not amperage. See is the problem goes away.
The Autopian scores a coup! David Tracy’s Spirit Car Hoarder has come over from the dark side! Hallelujah!
Glad to see you are hitting the ground running with articles. Always welcome a familiar voice here (along with ones I have not heard).
Another thing to add to my “Why the heck did it do that?” list. I have seen other parts cause a slew of errors but not a 12v battery. Granted that is much cheaper than the battery pack.
I was just driving my girlfriend’s 06 Equinox as the alternator tanked and the battery voltage was dropping. It was flashing every kind of weird error as the dash display dropped from 11.5 to about about 7.5 when the instrument panel went out.
Modern batteries, at least those you buy from the chain stores, seem awful these days. I’ve had more than one fail within a year of purchase. Last time, I bought a Motorcraft from a Ford dealer for the Taurus. It was competitively priced with similar units from O’Reilly’s and Autozone, and three years on, it’s still performing like new (knock on wood).
Next time I may get an Optima.
The same manufacturer makes Duralast, Die Hard, Optima, and several other battery brands, Clarios LLC. Used to be made by Johnson Controls but they sold off their battery division in 2019.
So they’re all garbage, got it.
You’re just going to want to check carefully. Then again the Mopar battery that was in my Jeep is what was on its way out after 4 years and they’re a different manufacturer. Hoping Interstate does better.
Optimas are built differently.
Instead of horizonal cells built of stacked plates, an Optima is a spiral cell that should be much more durable.
https://www.autobatteries.com/en-us/battery-technology-types/optima-spiralcell-battery
They’re a premium product with a very premium design. They’re what I’ve bought for any convertible with a power top. That’s also what I’d buy for an offroader, or any RV that you’re likely to use out in the backwoods.
I wish I could find Optima batteries for motorcycles. (They’re not shown on Optima’s website.)
Agreed. They’re junk.
Weak batteries making cars throw other odd codes and behaviors seems to be becoming more common. There’s been quite a few threads I’ve seen on Wrangler JL forums about folks having their Jeeps freak out on them while driving and it turns out it’s because the aux battery is getting weak and needs replacement.
It also seems like they’re not lasting as long either, 3 years, 4 if you’re lucky.
I had to replace the 12V battery in my Volvo V60 this year. It started throwing weird errors with the blind spot monitoring system, but it did tell me that the battery voltage was low, so diagnosis was dead easy. Oddly enough, the battery I could find that was the correct form factor and everything was also a Motorcraft from Rockauto (who don’t charge a core on batteries, oddly enough).
I thought that was odd that you said they didn’t have a core charge, but I see for some V60s that a performance AGM might have no core charge. Otherwise most other batteries do have a core charge with RockAuto. Luckily you can arrange to ship the old battery to them to get the core charge refunded.
I had a 1992 BMW 525 for a while where the previous owner had mis-routed the serpentine belt.
The car would start fine and run for a surprisingly long time, but would eventually die.
The instrument panel would start to light up odd things just before it would die.
I recall the ABS light would come on just before the absolute end.
The computers, really, were pretty robust, but once the voltage got too low, they would misbehave.
If you know how the chips in a computer work, it isnt terribly surprising.
It makes sense if that’s actually the case. With all the types of electronics in newer and newer cars, you’d think power conditioning is likely becoming more of a factor.
And people wonder why I’m not worried about the coming rise of the machines. Our future cybernetic overlords will be just as susceptible to unexpected irrational behaviors from unreliable power sources… actually, that would explain the last 6 years.
Yup yup. My Fiat 500E hasn’t had any problems yet, but I’ve read lots of posts about all the weird and wacky problems that can be “caused” by a low-voltage situation with the 12V battery, which all magically disappear after replacing said battery.
You get an upvote for having a 500E.
Exact same thing happens on Volts. As soon as the 12v battery takes on step towards its grave, all sorts of weird symptoms. That, and you may only have a matter of a few days from the onset of symptoms to the battery dying completely.
I have a feeling it’s due to the 12v never seeing a starter load, so it gets lazy and out of shape without showing a significant voltage drop.
Exactly the same with the BMW i3. Alarmingly, one of the main ghost error messages will tell you that the ABS is malfunctioning and you should stop the car immediately.
Not an expert here, but would it be that complicated to have a “low 12v battery” error programmed into the computer? Most importantly for cars like hybrids and EVs, when the owners might not be aware that there is still a regular 12v battery under the hood.
I don’t think the lack of load is a problem. It’s that the 12V system doesn’t power the starter. That is, a plain ICE car with a dying 12V will totally fail to start, so it doesn’t even have the opportunity to check sensors. Even the stuff that’s checked before ignition becomes quickly moot because the cranking attempt drops voltage to the point that the computers just give up and shut off.
With a hybrid, a dying 12V can get a lot weaker and still power the little contactor, but drag down the whole 12V system. So, you get gremlins instead of a failure to crank.
A fellow VGG fan? I’ll be dipped!
Indeed! We watch every upload!
A guy really loves VGG, and I ain’t kiddin’ ya.
I appreciate the Prius for the unique, ground-breaking beast that it is. However, I drove one a few times (same generation as yours) and wanted to send it off the cliff after multiple arguments with the shifter, which seemed to want to ignore my commands.
I feel you, there. One time, we got stuck at a gas station after getting fuel. Hit the “start” button, move the shifter into D, then the car gets mad and tells me to hit the P button. It eventually got out of park after trying over and over for about 30 minutes.
I wonder what the heck that battery has been put through to get so bad after just a single year.
Probably unrelated, but I noticed hanging anything off the shifter knob in my 2012 would make it want to reset to Neutral from any other gear, possibly from vibration or any vehicle movement. Very frustrating! I wonder if the switch sensor is overly sensitive.
Haven’t had that happen on the 2022 Prius yet, but it’s only holding a couple of spare hair ties. 🙂
Bad grounding on the 12V system? I’m pretty sure I have a bad ground on my Matrix, but the battery keeps on even though it starts weak and the car is mostly old tech.
It sucks. I had to replace my 12V on my Prius, and in going through the forums, the 12V seemed to be a continued problem in the cars. Any drop in voltage caused a lot of problems in the cars especially with the MFD (display).