Turbocharging can be a lot of fun. An efficient replacement for displacement that uses spent exhaust gases to make horsepower, it can unlock serious horsepower and hilarious noises. However, as anyone with an older turbocharged car knows, boost isn’t so fun when it’s leaking out of its intended tract. Indeed, Hyundai just recalled more than 85,000 Sonata sedans because a boost leak of sorts might rupture the fuel tank.
According to the official recall document, models with the 1.6-liter turbocharged four-cylinder engine are being recalled because of a potential fuel leak risk. However, if you read a couple lines down, you get to a line rarely said in the history of the English language: “The purge control system check valve may gradually wear and malfunction, allowing a backflow of compressed air from the turbocharger to enter the fuel tank.”
That might seem like a mind-boggling failure mode, but let’s break it down. The fuel tank purge system in a modern car is plumbed into the air intake to keep air from fuel vapors that end up in the charcoal canister as part of a closed system. As such, it incorporates a little check valve so that vapor can flow into the engine air intake but air can’t flow back through the charcoal canister and into the fuel tank.
The issue Hyundai has been having is that these check valves have been failing to operate as one-way valves, and with the air in the charge pipes and manifold of a turbocharged engine being compressed and pressurized, a leaky check valve could mean pressurized air enters the fuel tank. Unsurprisingly, plastic fuel tanks can expand when fed pressurized air, and a pressurized Sonata gas tank could make contact with a sharp shield panel or the exhaust system with predictable results. Indeed, the potential symptoms listed in the recall document include:
A. “Pop” noise from the vehicle rear
B. Illumination of the MIL
C. Vehicle will not start
D. Fuel odor
Needless to say, fuel tanks aren’t meant to go pop. Also, fuel leaking onto a hot exhaust pipe is a great way to start a fire. Right now, Hyundai is aware of seven fuel tank leaks in 2020 to 2023 Sonatas across the U.S. and Canada equipped with the 1.6-liter turbocharged four-cylinder engine, which is enough to warrant recalling 85,043 examples in America and another 5,616 units in Canada. Unsurprisingly, the fix includes an updated purge control system check valve, but it also comes with a software update to monitor pressure in the fuel tank.
As far as problems go, this is one of the more bizarre ones out there, but it’s not unprecedented. The Sonata’s Kia K5 platform mate also suffers from the same issue, with 250,547 2021 to 2025 examples being recalled in the U.S. and another 2,737 units recalled in Canada.
On the plus side, Hyundai has a fix, and owners can expect a letter in the post come January urging them to take their Sonatas in for the free fix. In the meantime, it should still be safe to drive your Sonata, as the risk of a fire is rather small. Just, maybe keep an ear out for a popping noise?
Top graphic image: Hyundai
The Porsche 909 “Bergspyder” used a pressurized fuel tank instead of a fuel pump to save weight. Maybe Hyundai is just trying to replicate that.
“I like you deeply as a car and I’m going to choose not to even respond to that. *inflates your fuel tank making you big and round*”
Another reason why the base NA 2.5L is the engine to have. More power (198 hp to the 1.6T’s 180), nearly as fuel efficient (I saw 40 hwy), and probably more reliable now that the Theta issues have been ironed out (it’s technically not a Theta).
Nearly had the reverse problem on my lawnmower. I’ve heard of gas tanks collapsing due to a failure of the vent system to let air in to the gas tank. Mower would die like it was out of gas with plenty of fuel in the tank. Finally figured it out when I removed the fuel cap, heard a big “psshhhhh” and it started up again. I spent so much time cranking it with starting fluid, I’m lucky mine didn’t collapse too.
Lawnmowers—at least riding mowers—have a check valve to allow air in but prevent fuel from leaking out the vent in the event of a rollover. It appears that is what failed.
GM had a similar problem with the 1.4L turbo in the Cruze and Sonics. Only it was a failing PCV valve built into the plastic intake manifold that would fail. Then the turbo would back-flow and pressurize the plastic valve cover and blow out the valve cover seals, causing oil to leak out onto the exhaust and also into the spark plug valley under the ignition module.
In true GM fashion, they refused to issue a recall. If you were one of the fortunate ones who had one of these fail while under the factory warranty, they would replace the intake manifold, but would not warranty the replacement for another 3 years or 36K miles.
So there are a lot of Cruzes and Sonics out there with oil leaks.
Stuff like this is why we went with the 100,000-mile CarMax warranty when we bought a used Kia minivan. I still don’t fully trust it.
Maybe if they hadn’t made the gas cap sealed it could purge air and gases once it hits a certain level like a radiator cap.
EPA might have some thoughts on that.
Jokes aside, the fuel cap does have a safety vent that will open above a certain pressure. But I believe that is just to deal with a failure of the evap system. It probably can’t vent gas fast enough to deal with something like the turbocharger pressurizing the system.
Good to know thanks
And people wonder why others are skittish about buying a Hyundai.
All they need is a strategically placed and shaped exit valve, with an automatic piezzo electronic spark, and you would have jet power!
So after it blowed up real good, it would blow up real good?
One of my most fun days at work was when a manager went rogue and decided that instead of testing the fuel tank to three times it’s safe working pressure we should keep pumping it up until it failed. For science.
We had a little hand pump and we were using water to pressurise it so it wouldn’t properly explode, but we still had the tank outside and we had safety screens. After we’d all taken turns pumping and were all knackered we had this stainless steel tank that was obviously inflated, with a bunch of spot welds that had failed, but still no leak.
We kept pumping, then suddenly there’s a bang, and a splash. We looked out and the fuel pump wasn’t there any more.
We all started looking for it and then a few seconds later there was another bang when it landed.
Water isn’t very compressible, but steel is quite elastic,
In the early days of the automobile before they had fuel pumps, they would pressurize the gas tank to get the fuel to flow faster. The early Indianapolis race cars had a riding mechanic who among other things things would keep pumping air into the gas tank Google Spider Matlock.
So it’s sort of coming full circle. Well it’s not, but it’s a great opportunity to mention Spider Matlock.
“Turbo made the gas tank blow up” is some of the most Hyundai shit imaginable.
But a great song title.
Their offices need a version of those “accident” signs: It has been “0” days since our last major serious recall.
20052010201520202025 “This isn’t the same Hyundai of 5 years ago, you know.”Still far from Ford Frequently Ordering Recall Delivery
Three of three family members with new Hyukias in the last ten years have needed engines and an ex had an Elantra practically fall apart around her like the worst domestic small cars of the malaise era built thirty years before. I had two Fords. The total recalls for both were for a potential missing washer on the wiper arm (I checked and it was there), some software update for the manual transmission that I had done, and a reprogram for the hatch button so that it wouldn’t allow it to open over ten mph or something (also didn’t bother). Fords have a lot of problems and while I would be hesitant to buy one if they actually made something I wanted, Hyukias are another level of trash. They’re junk, have always been junk, and likely always will be since company culture tends to get worse and I would contend that the enshitification of everything has accelerated this even more from historical trends. And all that for what—an ugly sedan or CUV?
I did manage to put 117,000 miles on a 2022 Ioniq without any problems, but I suppose as a hybrid, each half of the powertrain only had to do a portion of those miles
Also, I went a bit over recommendations on preventative maintenence, and it did end up needing shocks and struts at 100k
That’s also very quick mileage, which is easier, and not that high of a total. I talked to a guy who swore his Lamborghini Espada was perfectly reliable—just follow the maintenance schedule and actually drive it, that most people’s issues were down to the cars sitting too much. I think that was the guy who put NOS on it, too, but that could have been a different guy.
I was literally just thinking of my sister’s 2009 Sonata that always needed something and had an interior that turned into cracked plastic trash despite her taking good care of it. And the numerous alternators I’ve replaced on 2014 Sorentos. And and and…
Well that’s mildly terrifying
Round and round the purge control valve
The monkey chased Sonata
The monkey thought it all in fun
Pop goes Sonata
Eventually Hyundai will run out of ways to fail. Right?
“Oh come on, this doesn’t even cause a fire.” – Jeep.
How long is a month of Hyundais? About that long.
At least it’s not engines full of aluminum chips like brand T, no not that brand T, the other brand T.
This is precisely why fuel tanks should be supercharged, not turbocharged.
In my KV Mini 1 some of the output of the engine cooling fan is directed into both the top of the fuel tank and the top of the sight glass to assist with what is otherwise a gravity-fed fuel delivery system:
https://live.staticflickr.com/5088/5731724122_d1f23555a3_b.jpg
The car is 45 years old and the tank hasn’t ruptured yet.
This is wild to me since turbos have been using purge control valves for years and I have never heard of it happening. I really do not understand how this even gets to this point.
Apologies to Jeff Goldblum, but “Hyundai, uh, finds a way.”
Engineer, “this is where the purge control valve goes. We can use the same one from our XXX model”…
Accountant, “We can save .001 cents per unit by using this new plastic material in the valve construction”…
Management, “I can get a pretty good bonus by bringing costs down”…
I’m thinking use the butts of already smoked cigarettes. Recycle Reuse and regret
If you unscrew the gas cap and pressure is released OR air is sucked in (I have had both problems over the years), it’s a pretty good sign something is wrong with the evap system in general. But most don’t have any way to build enough pressure to inflate the tank – yikes!
Evap on my Fiesta is problematic (car won’t idle right after filling gas tank), but it’s a capless fuel filler!
Modern caps aren’t vented whether that sort of thing or an actual cap. Something is amiss with your tank venting or charcoal canister/purge valve, etc. But on the other hand if it isn’t setting a CEL, is it REALLY a problem?
Yea I looked it up and seemed like a PITA to address. It’s been this way for at least 5 years/60k miles. I just goose the throttle to keep the idle steady for a few miles. Only caused a CEL once (and is the only CEL the car has ever had in 109k miles) and is completely avoidable if I don’t fill the tank 100%
My dad’s F150 had this issue and it was the purge valve. Inexpensive and easy fix. Well easy on the F150, no idea on a Fiesta.
But this issue is already solved by a radiator cap.
The whole point of modern sealed fuel systems is to eliminate evaporative emissions by keeping fuel vapors contained, and burning them off in the engine. Not even remotely comparable to a radiator cap.
A car with an unsealed fuel system and no PCV system like my Spitfire pollutes more sitting in the garage with the engine off than a modern car does hurtling down the highway.