2015 Hyundai Sonata: misfire or rough idle

Filed Sep 10, 2026 · Engine, Transmission · VA

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.

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 7, 2026 · Engine · CA

Engine misfiring and low compression

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 Sep 22, 2025 · Acceleration, Electrical · GA

The engine light started to come on and go off and when I got the codes ran, it said something along the line of misfire. I had the spark plugs changed and I kept regular maintenance done on oil changes and tune ups. Now my engine is knocking and the vehicle is in limp mode.

Filed Jun 26, 2025 · Engine, Transmission · IA

Our 2015 Sonata has experiencing Engine failure several times due to excessive and irregular oil consumption. Our family’s safety and the safety of others on the roadway were put at risk as the engine slows, shudders and stalls without prior warning and the check engine light does not come on until the vehicle slows and stalls. The vehicle was inspected at a local Hyundai dealership, and they indicated that this is not covered under warranty. Summary of Engine Issues and Failures: 1.May 3, 2022 – 68,671 miles (local Hyundai dealer) Check engine light on, shudder; oil change performed. No cause identified. Paid out-of-pocket. 2.August 23, 2022 – 75,527 miles (retail shop) Car engines failed on highway, towed to service shop. Valve cover gaskets replaced. Paid out-of-pocket in part and extended warranty paid part of the invoice. 3.April 29, 2024 – 109,229 miles (local Hyundai dealer) Excessive oil consumption noted; valve cover gasket replaced again. Paid out-of-pocket. 4.January 22, 2025 – 118,341 miles (local Hyundai dealer) Vehicle stalled en route to airport, towed to dealership; dealership advised oil change. Paid out-of-pocket. 5.May 20, 2025 – 122,000 miles (local Hyundai dealer) Engine codes P0300, P0302, P0303 identified. Dealer diagnosed excessive oil consumption likely due to ring wear or sticking rings, contributing to spark plug misfires. Recommendation: Engine replacement. Despite consistent and timely service, including multiple visits to the Hyundai dealership, the root issue has not been properly addressed. The current diagnosis of internal engine failure is a clear continuation of a pattern of unresolved engine problems (stalling in motion, oil leaks and oil consumption) all of which originated well within Hyundai’s original warranty. The vehicle has been well maintained, and all recalls have been addressed in a timely manner. Hyundai’s failure to acknowledge and take responsibility for this widely documented engine issue is a safety concern.

Filed Jun 20, 2025 · Brakes, Electrical · CA

The car has had an electrical issue ever since taking to to get a recall around may of 2023. It will randomly brake and shift the transmission badly while downshifting. I feel as if my make and model falls under the theta II campaign they had to replace certain engines for having a knocking rod be fault and release shaving into the engine causing it to misfire. Not only that but the electrical issue is completely random it happens atleast once or twice a week. It had began ever since I took it for a recall, and when I took it back they found no issue and left food in the back of my car and the chairs leaned back. This was the Fontana Hyundai dealership

Filed Feb 15, 2025 · Engine · CA

In 8-2021 the original engine locked up due to a crankshaft bearing lock up. The dealer replaced the entire engine with a rebuilt. It locked up within 10 seconds after I drove from the dealer due to a massive external oil leak from the engine front area. The dealer could not determine where the leak was coming from and prepared a report to reflect this. The dealer then replaced this first replaced engine with another rebuilt engine. I drove it and within 5 minutes of driving the radiator plastic side tank exploded open and lost coolant. The engine then misfired and began to smoke out the tailpipe. and engine areas. The dealer demanded I pay $1,100 for a replacement radiator and then they would confirm that the head gasket was leaking from the combustion chamber into the cooling system that exploded the radiator side tank due to overpressurization from exhaust gas. Another dealer saw that the combustion gas had a large leak that was coming out of the broken radiator plastic side tank and advised repalcing the engine with another engine and radiator. The engine locked up while driving it as a result of overheating and/or coolant inside the cylinder that has the head gasket leak. The dealer and factory refuses to repair the engine that is still under two different kinds of warranties. The warranties expire on 10-12-2025

Filed Dec 23, 2024 · Engine, Fuel system · OH

Approximately five weeks ago, my 2015 Hyundai Sonata showed a check engine light. I took it into the dealer and paid a diagnostic fee which revealed the third cylinder misfire in the engine. I paid to have the engine cleaned yet the light continues to stay on and the car has been Running low on oil every time it gets checked the dealer states that the engine needs to be replaced

Filed Sep 22, 2024 · Brakes, Electrical · CA

I took the car for 4 recalls it had 2 of which were physical and the other two were software according to them. Took the car back to drop someone off, turned it off and then on; it began losing and breaking on its own at slow rpm’s slamming on the breaks. a minute later after having turned the corner I turned on my hazards and it had continued to randomly happen to the car. It is not consistent it is completely random and I have had a mechanic only inspect it while it happened once because I’ve only been able to have it happen while being inspected out of luck . I’ve gotten several error codes to the car since from p04 misfires. Evap leaks etc. the car was in pitch perfect condition and after that day it has since stopped working properly . I have photos of the mechanics that day even leaving food in the back of my car as if they just relaxed and didn’t do their job as professional as it could’ve have been . They denied anything is wrong with the car and have offered me discounted inspections after claiming nothing was wrong they gave me one free inspection and I haven’t gone back . My engine or censors are messed up. It puts my health and others at safety because it slams on the breaks unknowingly and randomly at low RPMs. The manufacturer has inspected my car and claimed it was okay although they unprofessionally left food and ate breakfast and left trash in the back. (With photo proof) . Last there was NO issues whatsoever with my car until that day. Never had a misfire . Never had a engine light . Never had a popped tire . It all began they DAY I got my car back not even an hour later. I could not return that day because it was near closing time of the dealership and the day after I went they denied it has been tampered. This happened around the beginning of July 1-8th 2023.

Filed Feb 28, 2023 · Engine · OH

Ports internal to valve cover were blocked. Oil blowing out of valve cover jacket, filling spark plug wells and causing misfiring. Concerned about fire hazard for all leaks.

Filed Nov 15, 2022 · Acceleration, Engine · NC

told the Hyundai dealer 2 years(March 2021) ago that I was concerned about my oil light flashing periodically between scheduled oil changes. No action other than oil changes and one time they added a couple of quarts "no charge" as it again was low. Continued to change oil more often than necessary and the frequency increased. Multiple other car repairs have been happening and the oil now has to be added weekly to maintain proper amounts. Had to change spark plugs 2 times with in 5 months and now another engine light came on today 11/15, and when I check the code at a parts store I was told is was a P03001 and P03002 which was something to do again with the cylinders misfiring. Everyone I have spoke to says this is an engine issue and it is under recall. I did place a claim with Hyundai Care USA after being told by the dealer that it would be better if I did this instead of them. The assistant manager also confirmed that the engine is covered 100%. I did this in September after the second repairs. The Regional Manager finally called me back and indicated he agreed about the problem needing to be resolved and would call me after he spoke to the dealer in a day or two. It has been over a week and no one has called. I keep leaving messages. I now have the same error codes, it is November 15 and the spark plugs were all changed less than 2 months ago for the exact same reason. I have been stranded and at times when I accelerate onto traffic the car will not respond. I do not use the interstate anymore as I cannot predict when the car will slow down and not get enough speed and cause an accident. I only drive to work and back right now. I was given this website by the employee at the parts store along with some information concerning P1326 codes and they are engine related. I will upload the most recent repair receipt.