2015 Hyundai Sonata electrical system problems

“On Wednesday, October 21, 2026, our 2015 Hyundai Sonata with the 2.4L Theta II GDI engine suffered a sudden, complete engine seizure while traveling about 75 mph on I-25 Southbound near Castle Rock, CO. A family member was driving. Warning lights across the car began flashing, the engine made a loud grinding noise, and the brakes stopped working. Over a long distance, the driver was able to get the car onto the shoulder and bring it to a stop, then engage the parking brake. There was no collision and no injuries, only because traffic was light. The car was towed to a repair shop, then transferred to a second shop, which determined the engine had seized and requires full replacement. This vehicle is covered by Hyundai's Theta II GDI engine campaigns for connecting rod bearing failure. On October 26, 2026, Hyundai told us the Knock Sensor Detection System software update (Campaign 953) was never completed on this vehicle and declined coverage. Neither we nor the prior owners, who are family members, recall receiving any notice of this campaign. All previous check engine lights were diagnosed and repaired at independent shops, including an intake manifold…”

“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…”

“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.”

“Odometer Fraud. The contact purchased a 2015 Hyundai Sonata. The vehicle was a private sale. The vehicle was purchased on March 1, 2026. The mileage at the time of the purchase was 41,486. The vehicle was taken to the dealer, where the contact was informed that the odometer mileage was last reported at 223,718. The seller was not made aware of the discrepancy.”

“I was driving on the highway and the engine shut off but everything else remained on. I drifted to the breakdown lane and turned the car off. It would not start again and the car began acting up by turning lights on and off, telling me to check the tire pressure, and not unlocking the doors. I then saw some very light smoke from the engine compartment. I popped the hood and looked and saw a glow on the bottom side of the engine area. Then the car just went up in flames.”

“My 2015 Sonata will stall out dropping speeds to 12-24 when i slightly merge, when I turn ect. Then it won’t accelerate for what seems like 10 minutes realistically 2 minutes maybe 3 Then will slowly regain speed. I’ve almost wrecked twice Share care with daughter and she’s been victim to it way way more. This is scary and Hyundai won’t stay behind their product Local dealership won’t fix recalls so we have to go over 120 miles for repairs. The recall isn’t even for transmission engine”