2015 Hyundai Sonata Owner Complaints

After receiving the Hyundai Service Campaign 9C2 update on my 2015 Hyundai Sonata on XXX, I have started having jerky acceleration when the car is first started and am driving. Also, while driving at highway speed (~65 mph)) and I take my foot off the accelerator to coast, the engine RPM drops suddenly, anywhere from 250 rpm to 750 rpm, then recovers abruptly to where it was at prior to the drop (typically around 2000 rpm). The engine rpm also drops while driving at slower speeds and recovers but is not as noticeable as it is at highway speeds. It was not doing this prior to the Service Campaign. There are no check engine lights or pending codes. I brought it back to the Hyundai dealer and discussed the issue with them on XXX. They acknowledged it was likely due to the Service Campaign and they did not want to keep the car to look at it and said no damage was being done and it was safe to drive. They said a fix was in the works but did not know how long until it was released and I should receive information in the mail on it. Video link [XXX] INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA ID

11763571

Incident

Aug 17, 2026

In March 2026 Hyundai did an emissions update Campaign 9C2. Since that update my 2015 Hyundai Sonata SE has run rough and shifted hard. Hyundai stopped doing the update in May 2026. Hyundai has not provided any update to fix the problem they created. I am worried the update is damaging the motor and transmission of a car that was running just fine prior to the update.

NHTSA ID

11763289

Incident

Mar 12, 2026

The engine failed due to the known recall defect, dealer confirmed loss of compression in cylinders 2 & 4. I am a federal employee stationed overseas on official duty orders, and Hyundai Motor America is delaying safety recall remedies and buyback negotiations since June 9th.

NHTSA ID

11761235

Incident

Apr 27, 2026

Engine locked up, crank bearing failure, found out there is known failures with this problem and Hyundai had a class action suit against them in the past and issued lifetime warranty for this engine due to this problem. Took car to local dealer, Clay Cooley in Sherman TX, they have been great but Hyundai corporate has denied the claim stating lack of maintenance records. Car has 175,000 miles on it, I have only owned it for about 5-6,000 miles. I have changed the oil in it twice myself I was able to prove one of those with a receipt but I don't have the other receipt and have been unable to get it. The dealer has records of oil changes up to 150k miles then I was able to find additional proof of other oil changes through car fax at smaller lube shops. The previous owner before me changed their own oil also and did not keep receipts I reached out to them with no luck. Ultimately there is only about a 10k mile gap of unprovable maintenance, this engine model has a known issue, it did not make it to 175k miles without proper maintenance, I can't control what previous owners did with their receipts but lifetime warranty should be lifetime not only if you can prove every detail from people you can't control.

NHTSA ID

11759964

Incident

Jul 28, 2026

I bought this car new in 2015, when I was at 97000 miles they had to replace the motor and turbo, I am now at 155844 and they are telling me that basically all 4 cylinders have low compression, cylinder 3 is the worst. They are telling me that this car has to have a new motor. I have not done anything to this vehicle to cause no compression. They want me to pay around 8800.00 to get this fixed.

NHTSA ID

11759071

Incident

Jul 21, 2026

Issue- fuel pump/supply line causing fuel to leak and fuel smell around the outside of the car. This can cause a major fire, explosion, death for myself and others around me. Problem has been confirmed by auto repair shop. No warning messages on car dash board, just strong smell of gas. Replaced gas cap and smell is still there.

NHTSA ID

11757985

Incident

Aug 3, 2026

Brake lights not working properly.

NHTSA ID

11757315

Incident

Aug 16, 2026

My Hyundai Sonata engine stalled out while driving on the highway. I had it towed to a dealership with the hope they would fix the issue because it was supposed to be covered under warranty from a recall. The dealership said the engine replacement would be covered as long as they got approval from Hyundai. Hyundai apparently only asked that specific dealership for the service records that they had, didn’t even reach out to me or try to find any other service records on the vehicle and denied the claim for “neglect of maintenance” because that dealership only had records from 0-90,000 miles. The dealership got back to me and told me the news and I told them that I will get all service records from 0 miles to current. I got all those records together and sent them to the dealer. A week later they called and said Hyundai was again going to deny my request because of the same “neglect of maintenance” which isn’t true based on the records I have and they have. I have driven the vehicle less than 10,000 miles and there has been nothing wrong with it. No check engine lights ever and regular oil changes.

NHTSA ID

11756074

Incident

May 16, 2026

The contact owns a 2015 Hyundai Sonata. The contact stated that while driving on several occasions at various speeds, the vehicle lost power, and the check engine warning light was illuminated. The vehicle was taken to a dealer where it was diagnosed that the engine had failed and needed to be replaced. The vehicle was repaired, but the failure reoccurred within a year. The vehicle was taken back to the same dealer where it was diagnosed and determined that a software update was needed. The vehicle was repaired, but the failure persisted. The vehicle was then taken back to the same dealer, and there was oil on the pistons and a tune-up was needed. The vehicle was repaired, but the failure persisted. The vehicle was taken back to the dealer, where it was advised that an oil consumption test could not be provided until the pistons had failed. The manufacturer was notified of the failure, and a complaint was filed. The failure mileage was approximately 88,000.

NHTSA ID

11755866

Incident

Jun 29, 2019

Mileage

88,000 mi

Vehicle: 2015 Hyundai Sonata VIN: [XXX] Mileage: ~85,000 Description of the Problem: While driving, the vehicle suddenly began producing thick smoke from under the hood without warning. I safely maneuvered to the shoulder to avoid an accident. The engine subsequently seized completely and became inoperable. My mechanic diagnosed this as a known internal manufacturing defect in the Theta II engine (connecting rod bearing failure), a widely documented issue for this model and production year. Oil and coolant levels were confirmed normal with no leaks, ruling out maintenance neglect. I initially paid for an unnecessary starter replacement before this diagnosis was confirmed. This is a serious safety hazard that could cause loss of engine power and control while driving, posing a risk to myself and other drivers on the road. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA ID

11755594

Incident

Aug 6, 2026

1.) Following Hyundai's 9C2 Campaign update for the ECU that was completed back on May 27th, 2026, my 2015 Sonata went into limp mode [solid check engine light present] while I was accelerating up an on-ramp on the 2nd drive cycle since the update was performed. I was already far away from the dealership so I was forced to limp it to my local shop that I regularly use to have it checked out. It was confirmed that the code on the vehicle was P200A for intake manifold runners. Since the update was for smog regulation, the code was cleared in order to see if it would come back. Since then, it has not, however the vehicle continues to have one persistent problem. The RPMs will dramatically dip and then surge back upwards while the car is coasting (no gas and no brake applied). 70% of the time, you can feel the car violently jerk as it appears to try and correct itself. 2.) I've brought this car to multiple dealerships, have a case open with corporate and have also found that this is a systemic issue with this specific update in these cars. All and all, nothing has been done. I'm repeatedly turned away over and over again because their techs are only permitted to look into it once they have hard evidence of a fault. In this case, that would be a dashboard light. I'm told that I may only return if the check engine light comes back, which as I mentioned previously, posed a HUGE safety risk to myself the first time it appeared. If I can only go 55mph down the highway, I am at risk of being rear-ended or struck in some way. 3.) The problem has not been reproduced by the dealer as they will not test drive it to see the dip and spike. However, the code was still pending for awhile in the vehicle before it cleared it on its own, so that was acknowledged by at least one place. 4.) Vehicle has not been inspected by anyone but a dealership and local mechanic. 5.) No other signs prior to the vehicle limping out on me other than some acceleration concerns on May 27th, 2026.

NHTSA ID

11755317

Incident

May 27, 2026

Since the 9C2 update on June 24, 2026, my vehicle has not driven the same. I'm experiencing clunky or harsh gear changes at low speeds, especially during stop-and-go driving. When I slow down and then accelerate again, the vehicle sputters or hesitates before responding. While driving at lower speeds, I also feel intermittent skips or small surges, almost like bubbles or brief misfires. These symptoms were not present before the 9C2 update, and they have noticeably affected the drivability of the vehicle. It was suggested the transmission needed time to "relearn" driving patterns, but it has been several weeks with no change

NHTSA ID

11755188

Incident

Jun 24, 2026

Engine / Short block assembly / Connecting rod bearing seizure. The engine suffered a sudden, catastrophic seizure while I was actively driving on a steep incline mountain road with a cliff on one side and forest on other. The vehicle experienced an immediate, total loss of motive power, forcing an emergency maneuver onto the shoulder in 5 seconds with no power steering or power brakes, creating an extreme collision hazard on a high-speed incline. The rod bearing melted due to a manufacture defect and could have also possible caught fire in heavy fire country. The fuel pump was also leaking recently and just replaced. They are nearly $1800 for a new pump because of price gauging because they are in "high demand". The Check Engine Light was solid (not flashing) for a thermostat code (P0128) due to extreme internal friction/heat from the failing bearings. There were no flashing KSDS warnings or physical signs of engine overheating. My car was denied a new engine under a Federally Mandated Warranty explicitly stating the exact symptoms of internal engine defect that happened in my car under "owner neglect" even though I have changed my oil regularly and even before the manufacture recommended time frames to do so. I've changed the valve covers, 02 sensors, thermostats, and plenty more on this car than any other car I have ever owned proving I'm actually an exceptional owner. I remained nice to all corporate staff during this process while they denied my car proper care under a Federal Mandate. I bought this car to believe that Hyundai was a superior company in regards to warranties, price, and function as opposed to the more expensive counterparts of the same class. Which in the end has cost me way more, and almost my life. This car is dangerous and the company has done everything in their power to try to cover it up while placing blame on the very consumers that are believing in them to do better.

NHTSA ID

11755077

Incident

Jul 3, 2026

Driving vehicle at slow speed crossing an intersection and engine completely shut down. The engine has completely seized and needs replaced due to a known recall. I have only owned the vehicle for 7 months. Hyundai is refusing to pay for engine replacement claiming a previous recall prior to me owning the vehicle should have been completed. I only drove the vehicle 1,000 miles in that time at nothing over 50 mph. There was no notification to me about this recall.

NHTSA ID

11754029

Incident

Jul 15, 2026

I was driving my 2015 Hyundai Sonata approximately 35 mph after leaving the Hyundai dealership following an engine replacement when the hood unexpectedly flew completely open without warning. The hood struck the windshield, completely obstructing my forward visibility and creating an extremely dangerous situation. I was able to safely pull over without causing a collision, but the vehicle sustained extensive damage and was declared a total loss by my insurance company. During the same service visit in which the engine was replaced, the dealership recommended replacing the hood latches, but I declined that repair. Hyundai later informed me that the hood latching system was functioning properly after the engine replacement and that the vehicle passed its post-repair inspection and road test. Approximately one mile after leaving the dealership following the engine replacement, the hood unexpectedly opened while I was driving. There were no hood-ajar warnings, warning lights, or other indications that the hood was not properly secured before the incident. The sudden loss of visibility created a serious risk of a crash that could have resulted in severe injury or death. I am submitting this complaint because I believe this incident represents a significant vehicle safety issue that should be investigated.

NHTSA ID

11753510

Incident

Jun 29, 2026

We are the sole owners of the 2015 Hyundai Sonata. Over the years the dashboard has deteriorated and developed cracks along the entire length, including over the area of the passenger airbag. We are currently concerned as to what would happen in the event of an accident that would trigger the air bag causing the dashboard to explode and send splinters all over the place, possibly causing severe damage to the passenger. I took the vehicle to Lehman Hyundai and they could not give me a definitive answer as to whether this was a dangerous situation or not. They gave me an oral estimate of $3,500 just for the part, and who knows what the labor costs would be. Whether I end up donating, gifting or selling the car, I am truly concerned about the safety of this vehicle and the condition it is in.

NHTSA ID

11753166

Incident

Jan 1, 2026

This vehicle had a recall, 201, for the smart junction box. This was due to the blinkers not working properly. The software update was performed, however, the problem still exists. This was due to the smart junction box. Now, aside from the blinker issue, the ac stays on when the engine is turned off, lights come on by themselves, the media screen goes randomly into night mode, daylight running lights are constantly in night mode, smart junction box failure. I have not taken this to a mechanic as of yet, the dealership is aware, and I opened a case with Hyundai case #42940056, however, I have not received a call from my service advisor or Hyundai. They offered to do diagnostics, but, if these problems are not about the safety recall, I would have to pay $350 for diagnostics, unless I get the problem fixed by them. This car has 66k miles with a new engine installed at 59400 miles! At this point, I have the car parked, battery disconnected, and looking for the most efficient way to fix the problem, which must be performed by specialized equipment.

NHTSA ID

11750940

Incident

Jul 2, 2026

On June 22, my 2015 Hyundai Sonata suddenly lost all electrical power without warning. The vehicle stalled and would not restart. There were no warning signs beforehand. After the incident, the car had no electrical power and was inoperable. Further inspection determined that the engine had failed and required replacement. I maintained the vehicle with regular oil changes and was unaware of Hyundai’s Service Campaign 953 (KSDS update). I was never notified that this campaign needed to be completed, and I believe that failure to receive notice contributed to Hyundai’s denial of my engine replacement claim. I purchased the vehicle December 19, 2019. I was never notified by the dealer or manufacturer

NHTSA ID

11750143

Incident

Jun 22, 2026

I had the Service Campaign 9C2 and TSB 25-01-087H recall emissions update performed. I immediately noticed degraded performance with my vehicle. It's very jumpy/stuttery after I first start driving and feels less responsive. Even after driving for a bit, it feels like it drives and shifts oddly. It is not as smooth as it used to be. My car drove fine prior to the update and immediately felt different after the update. It's now been over a week and it's still like this, so it's not the engine computer adapting or something like that.

NHTSA ID

11749467

Incident

Jun 30, 2026

The contact owns a 2015 Hyundai Sonata. The contact stated that the vehicle was taken to a local dealer who performed an emission software upgrade. Later, while driving, the air conditioner blew hot air, the thermostat increased to high, and an engine overheating warning message was displayed on the instrument panel. The vehicle was taken back to the dealer, who diagnosed that the thermostat had failed and needed to be replaced. The thermostat was replaced, and the failure was remedied. The manufacturer was notified of the failure. The failure mileage was 74,000.

NHTSA ID

11749309

Incident

Jul 2, 2026

Mileage

74,000 mi

The contact owns a 2015 Hyundai Sonata. The contact stated that while operating the vehicle, exhaust fumes were noticed inside the cabin, and the check engine light illuminated before the engine stalled. The vehicle was towed to a local dealer. The cause of the failure was not determined. The manufacturer was notified of the failure. The failure mileage was unknown.

NHTSA ID

11749278

Incident

Jul 9, 2025

Engine misfiring and low compression

NHTSA ID

11748832

Incident

Jul 4, 2026

Oil consumption

NHTSA ID

11748575

Incident

Dec 31, 1969

VEHICLE: 2015 Hyundai Sonata, 2.4L Theta II GDI engine Mileage at time of incident: [ 93k Date update performed: June 2026 Dealer/location where update was performed: Fitzgerald Hyundai Gaithersburg, MD DESCRIPTION OF PROBLEM: After my vehicle received the ECM software update issued under Hyundai Service Campaign 9C2 (ECU Software Update for Theta II Emissions Improvement, TSB 25-01-087H / 26-01-013H-1), the vehicle began exhibiting noticeable jerking/hesitation during acceleration that was not present before. For this vehicle this happens consistently after a cold start then does not happen again.

NHTSA ID

11748280

Incident

Jul 1, 2026

The incident began following a routine maintenance visit on March 16, 2026, and has been a continuous, ongoing safety hazard every single day since. While the vehicle was in for routine brake service and an oil change, the dealership automatically applied an open, manufacturer-mandated ECU S/W Update THETA II (26-01-013H-1) under Service Campaign 9C2 Emissions (Code NP001-SC9C2) without my prior knowledge of its drivability side effects. This software flash directly compromised the vehicle's powertrain logic, creating two notable, daily safety failures. First, within the first 5 minutes of engine startup, and most pronounced on every cold engine startup, the throttle delivery is highly erratic, causing uncommanded low-speed surging. In a specific incident in a parking lot following a cold start, I accelerated to approximately 15 MPH and completely removed my foot from the accelerator pedal to coast. Instead of slowing down, the vehicle unexpectedly lunged and pulled ahead forcefully against my intent. Second, even after reaching full operating temperature, the vehicle completely loses safe and predictable engine braking at greater speeds; when lifting off the gas pedal, engine RPMs aggressively drop, causing the vehicle to coast freely as if in neutral. Re-applying the accelerator causes a violent "phantom shifting" downshift and a hard transmission lockup. My safety and the safety of others are put at risk every time the vehicle is driven. The low-speed throttle surging creates an ongoing risk of hitting pedestrians or cross-traffic, while the permanent loss of predictable engine braking drastically extends stopping distances. No warning lamps or diagnostic trouble codes (DTCs) appeared prior to or during these continuous failures. The vehicle remains available for inspection.

NHTSA ID

11746404

Incident

Mar 16, 2026