general problems of the 2015 Hyundai Sonata - part 1

Am seeking assistance regarding a sudden and unexpected engine failure with my vehicle. The Sonata only had approximately 80,000 miles on it when the engine failed. Prior to this happening, I had never experienced any problems with the vehicle. There were no warning lights or other indications that there was an issue with the engine, and the vehicle had passed inspection. The engine failure happened completely out of the blue. I have also kept up with the vehicle’s maintenance, including regular oil changes. I recently replaced the battery and tires as well. Hyundai previously denied my claim, stating that the vehicle’s salvage title was the reason for the denial. However, I would like the circumstances of the engine failure and my maintenance history to be fully considered. The vehicle had relatively low mileage, was maintained, passed inspection, and showed no warning signs before the engine suddenly failed. I can provide maintenance records, receipts, inspection records, photographs, repair records, and any other documentation needed to support my claim.

A franchise dealership performed a federally mandated safety recall service (ecm software update) and a knock sensor replacement on this 2015 Hyundai Sonata 2. 0l turbo. To perform these specific repairs, the technician had to work directly around the intake and turbocharger assembly workspace. Immediately after picking up the vehicle, it suffered a sudden and dangerous loss of power and refused to accelerate normally on the highway, creating a severe traffic hazard. Upon an immediate emergency inspection by the same service center 5 days later, the dealership documented in writing that the turbocharger intercooler hose clamps were completely off/unfastened. Because the technician left the clamps disconnected, the turbo lost sealed pressure, failed completely, and began dumping high-pressure engine oil backward through the air filter intake box. The service center is now refusing to take responsibility for the mechanical safety failure directly caused by their technician's recall repair negligence.

Ever since the 9c2 software update was completed on 94/26, the car is experiencing hesitations not only in the first few minutes of driving but after the engine is hot. It was driving perfectly before this update.

"I am filing a complaint regarding severe vehicle jerking, engine surging, and rough transmission shifting immediately following the completion of Hyundai service campaign 9c2 (TSB 26-01-013h-1) on my 2015 Hyundai Sonata. The vehicle exhibits dangerous hesitation and lurching during cold starts. This behavior creates a traffic hazard when pulling out of driveways or into intersections during the first 3 minutes of operation. The manufacturer has acknowledged this cold-start defect in an internal 'drivability information' memo but has not provided a permanent remedy to repair the software logic. ".

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).

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).

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.

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.

I am filing this complaint regarding transmission and drivability problems with my 2015 Hyundai Sonata 2. 4l following Hyundai campaign 9c-2. My vehicle was running and driving perfectly before this update. I have always maintained it on time, followed proper maintenance schedules, and have records documenting its maintenance history. I never experienced these transmission issues before the update. The problems began immediately after the campaign was performed. In fact, I noticed the abnormal shifting before I even left the dealership after picking up my vehicle. Since the update, the vehicle has experienced poor and abnormal shifting behavior. I contacted the dealership to report the problem and also filed a complaint directly with Hyundai corporate. I was told that Hyundai is aware of the issue, yet my complaint remains unresolved. I also located a document online indicating that Hyundai is aware of this problem. Additionally, I have seen numerous reports from other Hyundai owners describing similar transmission problems after receiving this same update. My vehicle has approximately 82,000 miles. The engine was replaced approximately one year before this complaint. Given the vehicle's excellent operation before the update, my documented maintenance history, and the immediate onset of the problems at the dealership, I am seriously concerned that campaign 9c-2 caused or contributed to these transmission issues. I am requesting that NHTSA investigate whether this software update causes or worsens transmission shifting problems in affected Hyundai vehicles. Hyundai's awareness of the reported issue and the apparent number of similar owner complaints make this especially concerning. I believe this issue deserves investigation to determine its cause, assess any potential safety risks, and establish whether corrective action.

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.

Engine misfiring and low compression.

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.

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.

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.

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.

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.

Hyundai motor America is explicitly refusing to honor the mandatory safety recall and lifetime warranty extension for a catastrophic rod bearing failure on my 2015 Hyundai Sonata (VIN [xxx]). The engine suffered a sudden internal connecting rod bearing seizure while operating, causing a complete loss of motive power and creating an immediate hazard. Hyundai corporate escalations issued a blanket denial solely because the vehicle carries a rebuilt title. However, the vehicle's official Hyundai portal confirms that service campaign 953 (the knock sensor detection system software update) was successfully completed on xxx. The engine failure matches the exact factory manufacturing defect (internal oil starvation from manufacturing debris) that is the subject of the in Hyundai and kia engine litigation. The external collision history that led to a structural/rebuilt brand has absolutely zero mechanical correlation to a sealed, internal crankshaft block defect. Hyundai is acting in bad faith by using an unrelated title status to evade a federal safety recall mandate and escape liability for a dangerous, stalling powertrain defect. Information redacted pursuant to the freedom of information act (foia), 5 u. S. C. 552(b)(6).

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.

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).

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.

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.

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.

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.

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.

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!.

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.

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.

Car stopped on the road last week 4/6/26 could not start had to get towed mechanic says no oil in engine received oil change last month.

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.

My engine is a class action lawsuit and Hyundai refuses to honor their extended warranty because my title has a brand on it. (odometer issues) my car has been a the dealer for a month and Hyundai refuses even though it's a safety issue and a defect in their design. I want a new engine. The car is perfect otherwise.

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.

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.

Rod bearing failure.

The contact’s daughter owns a 2015 Hyundai Sonata. While driving and coming to a stop, the vehicle lost motive power. There was no warning light illuminated. The vehicle was towed to the dealer where it was diagnosed with engine failure. The contact was informed that the engine needed to be replaced. The vehicle was not repaired. The dealer informed the owner that the failure would not be covered under warranty due to a lack of engine maintenance on the vehicle. The owner provided the maintenance records. The manufacturer was made aware of the failure, and a case was opened. The failure mileage was approximately 124,000.

Check engine light is flashing on dashboard. Reduced vehicle speed. Car will not drive beyond 62 miles. Lost of power during acceleration.