2015 Hyundai Sonata

Engine misfiring and low compression

Oil consumption

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.

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.

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."

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.

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 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.

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)

The contact owns a 2015 Hyundai Sonata. The contact stated that while driving at lower speeds, the steering wheel became difficult to steer in either the left or right direction. The Traction Control, Power Steering, and the high-beam warning lights were illuminated. The vehicle was taken to a local independent service center, where it was diagnosed with error codes: C167286, C126008, C136008, C126002, and C168808. The vehicle was not repaired. 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 195,000.

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.

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.

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.

Car stopped in the middle of the road , with warning beeps and warning messages on the dashboard saying "Check Charging System" .Engine was still running but even though I did accelerate - car did not move . I put on the emergency lights and turned off the car . Turned on the car few seconds later and was able to drive then but the check engine light was on. Slowly drove back to the home as I was less than a mile from the home. It happened on a local road with speed limit of 35 MPH and thankfully vehicles behind me stopped until I pulled over. Me and and 7 year old kid was in the car at the time of this incident

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!

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.

My infotainment unit stoped working after an update that was pushed to the car by Hyundai. My battery was beginning to show signs that it needed replacing (not cranking in the cold temps or needing a few tries to start), so I went to Advance Auto to have the battery replaced. Once back in the car, everything was working fine (radio with sirius XM, back up camera, Navigation, Android and Apple car plan, the clock, everything). When I went to reset the clock, the car showed a software update was availabe and needed to be downloaded. Never before, had I seen this. So, I selected update. After 30 minutes of seeing it say downloading, it then started to say install. It gets to where it says, the radio needs to be restarted to complete the update and then gives error code 604. Now the telematics or infotainment works. I reached out to mapit, Hyundia and Bluelink who all say, "to bad for you, buy a new one for $1600". I did not ask for the update, I did not go looking for the update and I did not push the update to my vehicle, Hyundia did and me and the other 2000 owners who are going through this should not have to pay that kind of money to have it repaired. If they new they were shutting down 3G service, then don't push the update to my car. Hyundia has admitted the issue for Hyundia Tusons and a few other vehicles but not for 2015 model Sonata's. So for Tusons they send out 3 SD cards to fix the issue, but refuse to do so for all the cars they pushed an update to that as they called it Bricked the head of the unit. I am looking for help to get this fix without me paying $1600. If Hyundia recognizes the problem in some cars and not others thats an issue. One that we the public would love help addressing.

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