2018 Hyundai Sonata: hesitation when accelerating

Filed Aug 25, 2026 · Engine · NC

Since I had Service Campaign 9C2 completed, the car hesitates to start, does a mini-lurch upon cold start and runs rough. Two weeks ago, it was put in park, lurched backwards, then died. The starter and battery have been replaced but this has not helped. The car ran fine before this update was done.

Filed Aug 16, 2026 · Engine, Transmission · TX

I recently had the 9C2 Emissions recall update performed on my car, and since the update my car drives like total garbage after a cold start. It hesitates to accelerate, it bucks when trying to accelerate, and it’s to the point the engine is about to stall. I took it back to the Hyundai dealership and they said they are aware of the issue, but there is no fix from Hyundai at this time. This is a major safety concern, as the car barely wants to accelerate after a cold start. Please have Hyundai fix this safety issue.

Filed Jun 11, 2026 · Engine, Transmission · IL

Following completion of Service Campaign 9C2 (ECU software update, TSB 25-01-087H) at a Hyundai dealership, my 2018 Sonata immediately exhibited drivability changes that were not present before the service. Symptoms include altered shift timing, hesitation, and rougher throttle response — particularly noticeable during the first several minutes of driving. These symptoms began on the first drive after the recall update was applied and have been consistent since. The vehicle was returned to the dealership for inspection. No underlying mechanical issue was found, confirming the drivability change is directly attributable to the ECU software update. The vehicle has been maintained strictly per Hyundai's manufacturer-recommended schedule and had no prior drivability issues. I am aware that numerous other owners of Theta II-equipped vehicles (Sonata, Santa Fe, Tucson) have reported identical symptoms following 9C2. At least one dealership has reportedly acknowledged this as a known post-update issue that Hyundai is working to resolve. The altered throttle and shift behavior poses a safety concern, as unexpected hesitation during acceleration affects predictable vehicle control in traffic. The vehicle is available for inspection upon request.

Filed May 6, 2026 · Engine, Fuel system · TX

I am submitting this complaint to report a serious and ongoing safety defect involving the engine of my 2018 Hyundai Sonata Sport equipped with the 2.4L Theta II engine. The vehicle has been officially tested and documented by Hyundai as consuming more than two (2) quarts of engine oil per 1,000 miles, which Hyundai has acknowledged following completion of its oil consumption test procedure. Despite this confirmation, Hyundai has declined to fully correct the defect. As the condition has progressed, the engine now fouls spark plugs every 350–500 miles, resulting in: •Engine misfires •Loss of power during operation •Rough running and hesitation •Risk of sudden engine stalls while driving This condition occurs without warning and requires repeated roadside or emergency repairs simply to keep the vehicle operable. The condition has deteriorated further, requiring replacement of fouled spark plugs every 350-500 miles. Loss of power and engine shaking can occur at any time, presenting a safety hazard for me and other drivers.

Filed Jan 9, 2026 · Engine · 138,000 miles · MS

The contact owns a 2018 Hyundai Sonata. The contact stated that while driving approximately 60 MPH, the vehicle started to vibrate roughly. The contact felt the vibration in the steering wheel. The check engine warning light was illuminated. The contact slowed down and pulled off the roadway. The contact turned off and restarted the vehicle and was able to shift to drive(D); however, the vehicle was hesitating and failed to accelerate as needed. The contact drove the vehicle to an independent mechanic at speeds no greater than 40 MPH. The mechanic scanned the vehicle and retrieved codes for a misfire in the engine. The mechanic advised the contact to take the vehicle to a dealer for assistance. The vehicle was towed to the local dealer. The vehicle was not yet diagnosed or repaired. The manufacturer was informed of the failure. The contact requested an engine replacement that was denied by the manufacturer. The failure mileage was approximately 138,000.

Filed Nov 22, 2025 · Engine, Fuel system · OH

I am submitting a formal complaint regarding ongoing and severe engine issues with my 2018 Hyundai Sonata SE. Despite proper maintenance, the vehicle has developed extreme oil consumption and misfire problems that have made the car unreliable, unsafe, and financially burdensome. Beginning around 118,000 miles, the vehicle started consuming oil so rapidly that I was forced to completely replace the oil every 1–2 weeks because it would run dangerously low or nearly empty. This level of oil loss is not normal, acceptable, or sustainable. I have detailed documentation, receipts, mileage logs, and maintenance history supporting this. In addition to oil consumption, the vehicle has repeatedly misfired, produced diagnostic trouble codes, and fouled spark plugs with oil. I have been forced to replace spark plugs approximately every two weeks, which is clearly abnormal for any modern vehicle. On multiple occasions, the vehicle has experienced violent knocking noises, severe loss of power, hesitation during acceleration, and near-stalling. One incident was so loud and aggressive that it felt like the engine was going to come out of the hood. These symptoms pose a serious safety risk while driving. I brought the car to a Hyundai dealership at approximately 118,000 miles for an oil-consumption test. The vehicle failed that test, clearly confirming excessive oil consumption. Despite this, Hyundai refused to provide repair, internal engine cleaning, or engine replacement, claiming the vehicle was already over 100,000 miles I have maintained this vehicle responsibly and have documentation of regular oil changes, spark-plug replacements, inspections, and diagnostic reports. Despite my efforts, the issue continues to worsen, and the vehicle remains unsafe and unreliable. This ongoing problem has caused significant financial strain, emotional stress, lost time, and fear of engine failure while driving. Based on countless similar complaints from other Hyundai owners, this appear

Filed Aug 24, 2025 · Engine · NC

My 2018 Sonata has had an oil consumption problem since 2023. We initially thought it was the oil change garage issues. Had an oil consumption study conducted by Hyundai between July -September 2024. We were replacing 1,0 -1.5 qt oil every 700 - 1,300 miles. After the study, Hyundai told me I did not have an oil consumption problem. (Seriously?!?!) We had to replace the starter and now the spark plugs. Photo enclosed of how burnt the spark plugs were. Our mechanic was so mad that Hyundai was not honoring their warranty but allowing my engine and connected parts to just burn up. Hyundai told me to come in for another check tomorrow, 8/25/25. I called the Hyundai Consumer line on 8/18/25 (4th new case number in 13 months) and the person who answered the phone asked if I contacted a lawyer. I asked her if I needed to contact a ? I’ve been reading online about this problem today and found information about the federal safety agency and decided to file a complaint. This is dangerous because when the engine blows, I may be accelerating on the interstate and merging. That could be a fatal problem with this car. Traveling on the interstate on 8/10/2025 my Sonata stuttered and hesitated upon acceleration. We took back roads and limped home. My mechanic replaced the severely burnt spark plugs and told us our very nice car would be worthless soon if Hyundai did not fix this oil consumption problem. He called our Hyundai dealer on our behalf.

Filed Oct 27, 2024 · Acceleration, Engine · OH

My car is part of a campaign due to rod-bearing failure where the engine experiences problems such as complete failure, vibrating, hesitating, engine light on, and oil light on. I've been communicating with Hyundai who is not helping me with this issue. I was advised by them to continue driving the car "until the engine seizes", or I hear "a loud knocking noise". Upon inspection, three local Hyundai employees "agreed 100%" I need a new engine. However, per these employees Hyundai Corporate will not approve the replacement even though the vehicle is constantly experiencing the above symptoms above, simply because there is not a "loud knocking noise" coming from the engine. Even though ALL the other issues are present. This is very unsafe. I have a minor child I take to school daily, for an advisor to advise to drive the vehicle until "the engine seizes" is extremely dangerous, especially when they are aware my VIN is associated with engine replacement. My car exhibits symptoms of a rod-bearing failure and this multi-billion dollar company is taking advantage of hard-working urban mothers, by turning a blind eye and trying to require me to pay thousands of dollars up front for a problem THEY created by selling a vehicle with faulty engine. Again, the technicians indicated i in fact do need the engine replaced, but that Hyundai Corporate will require me to pay for a diagnostic test, rod-bearing test, and engine compression test because Corporate does not take their word for it. The fact a auto manufacturer is advising people to drive in such an unsafe manner is disheartening. If my child and I get injured in an accident by following their advice, our blood will be on their hands!

Filed Sep 15, 2023 · Engine, Transmission · PA

My car is misfiring, hesitating accelerating, severely shaking and vibrating which you can feel in the pedals and steering wheel, and the check engine light is on. This issue has been ongoing for over a week already. When the engine light first came on on 9/7, i pulled over on the side of the road and had a mobile mechanic check it out. The code was coming up as a bad ignition coil in cylinder 1. When he took out the coil and spark plugs, he saw scoring on the spark plug from oil as well as oil being consumed in the cylinder itself which has been causing my vehicle to misfire. The mobile mechanic stated on his invoice that I need a new engine. I took my car to Faulkner Hyundai on 9/11 and they said the best they can do is an oil consumption test even though they personally know I need an engine as well. I have not been able to drive the vehicle due to the ongoing issues, I am afraid for my life and safety that god forbid the car stalls out on the highway while I am traveling to or from work I could get into a major accident. They are putting my life in jeopardy.

Filed May 19, 2019 · Engine, Lights · 2,134 miles · CA

I purchased the 2018 hyundai sonata 2.0t on 8/27/18. After we were able to experience different driving conditions and situations, my husband and I noticed that (1) at night, while driving on the highway, the windshield appeared very dark as if it was heavily tinted,and making it difficult to see the road. (2) when driving on highway or road, with normal beam headlights, we noticed that the line of demarcation from headlight to dark road was very close to the front of the car. The reason given by the maintenance dept was that this was so cars in front wouldn't be blinded by the headlight. To us, it seemed that the headlights were aimed too low. I should be able to see more than 20 feet in front of my car. We were told that nothing could be done. Also, when making a turn, the area opposite the direction of the turn is completely dark because of the way the headlights work on a turn. This is extremely dangerous-should someone decide to walk there or if there is an animal, I will not be able to see anything. Again I was told there was nothing they could do. (3) my husband put rain-x on all the windows of the car. It worked on every window except the windshield. We thought there was some sort of coating placed by the manufacturer. I was told no there was not. They could not understand why the rain-x didn't take. They told me that they spent quite a bit of time "scraping the windshield", but nothing came off. We still do not know why it should do that. (4) I noticed. Whether I was driving in smart or sport mode, their is an annoying hesitation when I step on the gas. When the stoplight turns green, it takes several seconds before the car is able to move at normal speed. We were told that they received lots of complaints about that, but no offer for a fix.

Filed Apr 23, 2019 · Electrical, Engine · 11,000 miles · LA

On 03/23/2019, when I was leaving a parking lot my car started to hesitate and would not rev up. I just turned out the parking lot when this happened. Message came on stated it need to be serviced. At the same time the engine light came on. I was not able to press the accelerator because it would jump like crazy. I was able to get back to the parking lot safely. I have been in a rental for a month now and as of 04/23/2019 I was told the part is on back order. The wiring harness and the computer has to be replaced, but the tech stated since the car went into limp mode the engine will need to be replaced. I was told the part will be in about 3 to 6 months. If the wiring harness does not work god only know how many more months it will take for a new engine to arrive. This car was only 9 months old but now 10 months old with one of the months being in the shop waiting for repairs.

Filed Apr 17, 2019 · Engine · 8,087 miles · NY

Tl* the contact owns a 2018 hyundai sonata. The contact took the vehicle to fuccillo hyundai of syracuse (2601 erie blvd e, syracuse, ny 13224, (315) 445-7900) for a 4,000 and 8,000 mile check up. The dealer performed a computer check on the vehicle. The following day, the vehicle began hesitating and sputtering. The contact managed to drive vehicle home with the check engine indicator illuminating. The vehicle was taken back to the dealer and a loaner vehicle was provided. The dealer diagnosed that the vehicle may need a new engine and was waiting to hear back from the manufacturer. A month passed and the contact called the manufacturer. The manufacturer stated that the delay was caused by a large amount of people having the same failure. The contact researched the failure online and requested a buy back. After a few days, the manufacturer called back and offered a repurchase review and promised to call back. The contact received a call back and was informed that a repurchase review would take another month to review. The manufacturer stated that they needed to conduct research to see if it fell under the repurchase review or lemon law. The contact was still waiting to hear back and contacted his state's attorney general's office. The failure mileage was 8,087.