2015 Hyundai Sonata: hesitation when accelerating

Filed Oct 7, 2026 · Engine · FL

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.

Filed Oct 1, 2026 · Engine · CT

"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."

Filed Aug 6, 2026 · Engine · MD

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

Filed Jul 4, 2026 · Transmission · MD

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.

Filed Feb 19, 2026 · Engine · GA

Engine has knocking sound. Sudden loss of power and hesitation when accelerating

Filed Nov 24, 2025 · Transmission · NY

The engine/powertrain on my 2015 Hyundai Sonata (VIN: [XXX] ) has failed due to extremely low compression in all four cylinders, causing severe misfires, hard starting, loss of power, and intermittent rattling noises, and the vehicle is currently available for inspection at the Hyundai dealership. This failure created a safety risk because the engine hesitates, struggles to start, and can stall or lose power during driving, which could lead to a loss of control or an inability to accelerate in traffic. The problem has been confirmed by both an independent mechanic and the Hyundai dealership, who documented low compression across all cylinders. The vehicle has been fully inspected by the dealership on Hyundai’s behalf after I opened a case with the manufacturer. Prior to the complete failure, the car showed warning symptoms such as repeated cylinder 4 misfires, rough starting, reduced power, rattling noises on startup, and the check engine light appearing several times beginning earlier this year. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed May 15, 2024 · Engine · GA

Engine cylinder malfunction. Loss of power and choking, hesitation in moving forward. Could cause accident or traffic flow. Not confirm by dealer. But automobile is repair shop to determine problem.no warning signs are displayed.

Filed Oct 2, 2023 · Acceleration, Engine · MO

I am 86 years old. I bought the car brand new so I am the original owner. I have kept the car perfectly maintained and garaged from the day I bought it. My wife is also 86. She and I are the only ones that drive the car. To date, it has 73,822 miles on it. The main issue I am having is random, unpredictable stalling and hesitation when trying to accelerate. We have also had unintended acceleration. This always happens at the worst times which causes grave concern for our safety. We have taken the care to the dealership here in Cape Girardeau, MO called Chris Auffenberg Hyundai. They've charged me $130 only to tell me nothing is wrong. I have continued to try to work with them and they now have decided a new fuel pump will fix this which is $730. I have noticed there are already hundreds of complaints on the 2015 that all say they have the same exact issues I am having but this dealership doesn't seem to care. Here is what I have read. "The most common issue in the 2015 Sonata lies with its faulty throttle control system, which can cause stalling, hesitation, and even unintended acceleration. Currently, there is no fix from Hyundai." My dealership will not acknowledge this even though it is public information. I feel like they are going to keep replacing parts and are taking advantage of me. [XXX] is the Service Manager at this dealership and I am not happy how he is handling this. Please let me know if there is any additional information I can provide. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Aug 22, 2023 · Acceleration, Transmission · 95,000 miles · TX

The contact’s daughter owns a 2015 Hyundai Sonata. The contact stated that while the vehicle was idling, the vehicle hesitated. The contact stated that his daughter had to depress the accelerator pedal to rev the engine. The contact then stated that on a separate occasion while driving at an undisclosed speed, the vehicle hesitated and stalled. Additionally, the contact stated that on another separate occasion while his daughter was driving at an undisclosed speed, the vehicle unintendedly accelerated. The contact’s daughter was able to regain control of the vehicle and depressed the brake pedal to stop the vehicle. The check engine warning light was illuminated. The vehicle was towed to an independent mechanic where the vehicle remained. The cause of the failure was not yet determined. The vehicle was not repaired. The manufacturer was not notified of the failure. The failure mileage was approximately 95,000.

Filed May 16, 2023 · Engine · CA

Engine hesitation ( after throttle applied Engine acceleration ( w/no throttle applied Engine stalled ( with no code ) Dealer said because its intermittent & can not recreate & no codes found, there was nothing they could do. Icarus has stalled in the middle of intersection

Filed Feb 27, 2023 · Electrical, Engine · TX

A Aknocking noise from the engine that increases in frequency as the engine rpm increases. A Reduced power and/or hesitation and vibration. A Illumination of the "check engine" light in the instrument cluster.

Filed Sep 6, 2022 · Electrical, Engine · 80,000 miles · IL

The contact owns a 2015 Hyundai Sonata. The contact stated that after having her vehicle serviced under the federal safety agency Campaign Number: 21V749000 (Exterior Lighting, Electrical System) the exterior and interior lights would turn off while driving at various speeds, with the check engine and oil warning lights illuminated. The contact also stated that upon using the turn signals, the headlights would intermittently turn off; however, the headlights would turn on upon toggling the light switch. The contact had initially taken the vehicle back to the dealer where she was given a diagnostic fee to determine the cause of the failure. The vehicle was then taken to an independent mechanic where she was informed that the E-CVVT actuator was defective. In addition, the contact also stated that the vehicle would hesitate upon depression of the accelerator pedal or lunge forward upon depression of the brake pedal. The independent mechanic linked the failure to the E-CVVT actuator. The manufacturer was not notified of the failure. The vehicle was not repaired. The failure mileage was approximately 80,000.