2015 Hyundai Sonata Engine Problems

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

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

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

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

On October 2024,I brought the car in to RickCase Hyundai for maintenance and to address an oil leaking issue. I texted the service advisor, “Please do not do the oil change till you find out where the oil is leaking”, I’m replacing it frequentlyWhen I picked up the car and inquired about the leaking, the he told me that there was not an issue. January 2025, the car was driving rough again, noticed the oil low and filled it up. February 2025 driving on 595, The car stopped. I had it towed to Rick Case, they told me I needed to replace the piston. I said no this has to do with the oil consumption issue that I brought the car in October that you never addressed. The four new spark plugs that were put in were burnt on the tips. They went through the warranty issue to get the engine repaired and it was denied. I said this is not a warranty issue. This was a mistake on your part because you never address the oil consumption issue in October 2024. As of June 12,2026, the dealership still has my car. When I call and ask, What’s going on with my car. The only response I get is we are trying something else it’s going to take some time. Last summer, the service advisor told me he was going to fix my car, wanted me to come pick it up and drive it for 1000 miles and bring it back. They couldn’t fix the car. They never offered a loaner. The vehicle suffered a catastrophic engine failure and completely stalled in the middle of a live road, creating an immediate highway safety hazard. the vehicle is still being held at Rick Case Hyundai Weston for over a year regarding excessive oil consumption issues, which the dealer failed to resolve. The vehicle has 85,000 miles and a complete maintenance history. Hyundai Corporate is currently denying a replacement engine under the active engine settlement framework, leaving a known stalling safety hazard unresolved."

NHTSA ID

11743649

Incident

Feb 14, 2025

The contact owns a 2015 Hyundai Sonata. The contact stated that while idling at a stop light the vehicle suddenly stalled. The engine did not restart and the vehicle was pushed to a nearby parking space. During the failure no warning lights or messages had displayed. The cause of the failure was not yet determined. The manufacturer and local dealer were not yet contacted regarding the failure. The failure mileage was 123,000.

NHTSA ID

11742036

Incident

Jun 4, 2026

Mileage

123,000 mi

2015 Hyundai Sonata 2.4L Theta II GDI engine experienced complete failure due to connecting rod bearing defect. Vehicle was taken to a Hyundai dealership prior to failure to report engine knock symptoms. Dealer confirmed KSDS (Service Campaign 953) was installed but performed no inspection and provided no repair order. Engine subsequently failed with no warning light activation despite KSDS being installed. This is a known defect covered under the Theta II class action settlement lifetime warranty. Warranty repair has not been provided and no loner car has been provided.

NHTSA ID

11741060

Incident

Apr 30, 2026

The contact owns a 2015 Hyundai Sonata. The contact stated while driving at various speeds, the vehicle skipped and failed to exceed 35 MPH. The contact received notification of Hyundai Service Campaign Number: 9C2 (ECU SOFTWARE UPDATE FOR THETA II EMISSIONS IMPROVEMENT), and the vehicle was towed to the dealer, where it was diagnosed and determined that the catalytic converter was clogged and needed to be replaced at the owner's expense. The vehicle was not yet repaired. The contact's son, who was an independent mechanic, determined that the ECU might have sent erroneous signals to the O2 sensors, who then sent excessive fuel into the catalytic converter, causing a catalytic converter clog. The manufacturer was notified of the failure and was informed of the Service Campaign notification, but the manufacturer denied assistance due to the mileage and lack of warranty coverage. The failure mileage was approximately 140,000.

NHTSA ID

11740388

Incident

May 6, 2026

Mileage

140,000 mi

Was driving the vehicle up Berthoud Pass on [XXX] . Was a few miles past Berthoud Falls and realized that the vehicle power diminished, noticed smoke coming from the engine. Pulled over and noticed leaking underneath the engine. It appears that a bolt came loose and punctured the engine block. After further research, it appears that this engine recall should have applied to my vehicle, but did not: [XXX] INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA ID

11740144

Incident

May 25, 2026

In August 2025, my car went into "limp mode" (go no faster than 40 MPH and it was lurching and speed dropping) on the freeway, which was scary and dangerous. Once home, I called a certified mechanic. When this mechanic tried to start the car, it made a terrible clacking noise. He told me it sounded like the main bearings were going out. He discovered that there was a recall on this particular vehicle because the main bearings would fail. The local dealer confirmed that the car was subject to the recall and requested that the car be brought in. Because I am on limited income, I could not afford to have the car towed until November 2025. Once there, the dealership verified that the main bearings went out. A claim was made to the manufacturer. The claim was denied claiming "outside influence." I provided service records to the manufacturer, but before they had all the maintenance records, they closed my case and will no longer take documents or even speak to me or the dealer. I have been without a car for almost 10 months. I have seen documented cases that trying to start the car could lead to dangerous engine fires.

NHTSA ID

11738837

Incident

Aug 10, 2025

My vehicle has a lifetime warranty that is currently not being honored. It is currently in limp mode and showing a code P1326 which is an engine failure and possible fire hazard. The dealership has had my car for three weeks and have made no attempts to repair my vehicle which they are required to do by law under the Theta II Settlement. I was lied to by both dealerships. One stated my vehicle was branded as junk which was false. And now they are denying me due to mileage which shouldn’t be factor since the warranty is a lifetime warranty.

NHTSA ID

11737676

Incident

Mar 25, 2026

The contact's son owns a 2015 Hyundai Sonata. The contact stated that while the vehicle was being driven at 40-50 MPH, the vehicle began to jerk. The check engine light was illuminated. The vehicle was taken to an independent mechanic who determined the failure was related to the engine. The local dealer was not contacted. The vehicle was not diagnosed or repaired. The manufacturer was not made aware of the failure. The failure mileage was approximately 102,198.

NHTSA ID

11736934

Incident

May 3, 2026

Mileage

102,198 mi

On 5/27/2026 I was driving home from work. Had just gotten off the frwy , was driving around 35-40mph, all of a sudden , engine turned off, after coming to a stop, holding up traffic, i put in park, and nothing, not crancking, a new battery was imstalled, 3 weeks prior, have recoreds of all maintenance! Checked oil level was good, radiator, had fluid, and fas tank was 1/2 full! Pushed to a side street ,Uberd, back home, later that evening , had car towed approx 5 miles to my house. Checked all fuses, ignition, and starter! Spoke with Local Hundai Dealership, scheduled a maintenance diagnostic to be performed! Could have been an accident, first time, ever experienced, such an issue!

NHTSA ID

11735716

Incident

Apr 27, 2026

I have the 2015 Hyundai sonata with the 2.5 GDI engine that eventually will seize due to internal damaged caused by manufacture design flaws. My Hyundai threw a P0010 code which causes my car to idle high and causing low vacuum affecting my brakes. I had a diagnostic test done at a Hyundai dealership that told me it was a cvvt cam sprocket issue and that it was the beginning of the end of the engine, They quoted me 3700.00 but the engine was to far gone and this repair would only accelerate the engine to seize. They said since the engine isn't seize Hyundai will not cover the cost to repair or exchange the engine, I contacted the Hyundai customer service who stated since the repair that is needed wasn't the root cause of the problems associated with the engine swap warranty they were not going to help me even though I explained to them that the cars high accelerating and the braking system been jeopardized and been told the engine is beyond repairs I feel Hyundai should reconsider their decision and help a loyal customer. I have purchased 12 Brand New Hyundaj since 2001. The customer Representative was Extremely un Professional even suggesting I scrap my car, Also I contacted My Hyundai service Technician who said Hyundai customer service never contacted them about my car, When they said they spoke with the technician. Also I received an Extended warranty on the 2.4 GDI engine from Hyundai who many Hyundai customers are or have dealt with.I also purchased an Extended warranty Which I believe should have been extended as well Thank You

NHTSA ID

11735056

Incident

Apr 17, 2026

Engine – connecting rod bearing failure. Theta II engine. Hyundai confirmed the defect via Bearing Clearance Test (BCT) on October 3, 2025. The engine can seize without warning, causing sudden loss of power while driving – a clear safety risk. The problem has been confirmed by an authorized Hyundai dealership (Hertrich Hyundai of New Castle). The manufacturer issued Technical Service Bulletin 22‑EM‑001H (TXXI lifetime warranty) covering this exact defect. Despite confirming the failure, the manufacturer has refused to repair the engine. The vehicle is available for inspection upon request. No crash, fire, or injury occurred. Warning signs included engine noise and illumination of check engine light before failure.

NHTSA ID

11735022

Incident

Oct 3, 2025

since i have owned this car they have replaced the knock sensor twice. there is a recall on the engine for crank bearing wear, my car now is burning through 5 quarts of oil every 2 weeks with no oil leak spots on the ground. i would like them to replace the engine as per the recall. the knock sensor should be an indication of the bearings going bad. i have been getting the run around from the dealer in Salem, Oregon. so, i would like some assistance with this problem thank you for your time.

NHTSA ID

11732447

Incident

Apr 14, 2026