2018 Hyundai Sonata Complaints

ENGINE — Filed 07/13/2026

The lower aluminum engine oil pan developed a structural hairline fracture ("micro-crack") directly along the factory casting ridge adjacent to the drain plug. The component failed without any external impact, road hazard, scraping, or underbody damage. The failure was officially confirmed and documented by Eckert Hyundai during a service visit on July 13, 2026 (Case #42971835). Following the dealer oil service, the fracture degraded into an active, worsening oil drip that requires a catch tray under the vehicle to capture leaking fluid. The vehicle is currently available for inspection. Safety Risk: An active engine oil leak poses a significant safety hazard. Rapid or continuous loss of engine oil can cause sudden oil starvation, severe engine seizure, or total power loss without warning while driving at highway speeds, increasing the risk of a crash. Furthermore, dripping oil contacting hot exhaust or engine components presents a potential fire hazard. Prior Symptoms / History: This vehicle has a well-documented history of severe internal engine issues and thermal stress, including excessive oil consumption (running 1.2 quarts low in 1,127 miles), valve cover gasket failure, and severe drivetrain vibrations from failing front axles. The excessive internal crankcase pressure and thermal stress from these underlying defects contributed directly to the material fatigue and structural failure of this aluminum oil pan.

FUEL/PROPULSION SYSTEM — Filed 07/07/2026

Fuel line leak, car is parked, fire hazard, a mechanic has been there to inspect

ENGINE — Filed 06/09/2026

I purchased my vehical at Car Culture in Warren, Oh. The dealer said to only take it there for maintenance, so I did as required. Whenever the check engine light came on I would bring it there and they would say it was a sensor and they fixed it. And one day it started miss firing and the light came on again. When I took it to the dealership, they said it needed oil to bring it in every 2 weeks to top the oil off. And so I did that and finally the car was getting worse at 122,000 miles. When I took it there they said it needed a new motor!!!. They NEVER told me of a recall or a sensor replacement needing done by hyundai. Iam now stuck with a $13,000 loan on a car worth nothing without paying $5,000 on a "possible" fix for their negligence. I have a [XXX] old son, fiancee, morgage and a job im struggling to get to, because I was never notified of a possible recall on my year, make and model of car. Please help me. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

ENGINE — Filed 07/10/2025

Vehicle caught fire after repeatedly taking it to Hyundai for service . I complained about the oil consumption and knocking noises while the vehicle was still under warranty and it was denied.

POWER TRAIN,ENGINE — Filed 06/14/2026

Check engine light solid/engine failure while driving. 2018 Sonata SE purchased new in fall 2018. Around 50,000 miles started noticing oil level drop and had to add more before next scheduled change. Dealership service center said I just had to shorten the mileage between changes which didn't seem appropriate for a vehicle with 50,000 miles but I did. Continued to have oil consumption problem with no signs of leak, no burning oil smell or exhaust issues. Dashboard display would go off and when I immediately checked dipstick there was barely any oil so I'd add more then go in for full change. At 67,000 or so miles in June 2026, without oil display going off the engine light was now solid. Got to reputable service center near my home and oil was under a quart left yet the warning lamp hadn't gone off. They ran the engine error code P0304 and was misfire #4 cylinder and after compression test, #3 was very low and #4 very high. NOT drivable at that point then towed to dealership so yes, available for inspection by NHTSA at the dealership. For now they claim a 'tune up' is needed for spark plug replacement, valve cover gasket replace and fuel induction service that's my cost to incur which seems to just be fixing the damage of an engine oil consumption problem not fixing the issue that caused the damage. The engine seized/stalled without warning while I was driving the vehicle (granted at low speed in my neighborhood when the engine light turned on). I would not say the engine warning lamp occurred prior to the engine fail, it happed at the same time. This should not happen for a vehicle with my mileage and regular maintenance. I looked up NHTSA for potential recall or other helpful information and started to see extremely similar scenarios to mine and wanted to add complaint as well. This is getting very expensive outside of whatever cost the dealer wants as a fix with rental car needed and tow services. Thank you for your consideration of this engine safety issue.

UNKNOWN OR OTHER — Filed 06/09/2026

I was only in the car for about 4 minutes then came to a stop light. Once the light had turned green I pressured down on the gas, my car rolled for a second then died on me, causing it to go into accessory mode. Instantly three lights came on: the check engine light, battery light, and low oil light. The car would take at least 5 seconds to turn back on then would fall back into accessory mode randomly. Tried to jump the car 4 times, issue still remains. What sucks about this is that the mechanic shop can’t even figure out what’s wrong. They thought it was the high pressure fuel pump..turns out it’s not.

POWER TRAIN,ENGINE — Filed 03/14/2026

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.

POWER TRAIN,ENGINE — Filed 05/14/2026

The contact The contact stated that when taken the vehicle for a service campaign repair and shortly after went for recall r The vehicle does not run properly on cold starts, the RPMs increase rapidly and slow down, vehicle jerks forward once beginning to drive.. The vehicle does not have this issue once the vehicle is warm. The manufacturer was not notified of the issue. The approximate. Failure mileage was 47,575.

POWER TRAIN,ENGINE,FUEL/PROPULSION SYSTEM — Filed 04/04/2026

Engine blown out malfunction took two dealer Hyundai Folsom Lake stated rings are bad sludge buildup in engine and stayed at Hyundai motor America denied engine replacement due to knowledge under Theta two engine extended warranty settlement of 150,000 MI 15 years I'm still within warranty but are still being denied had numerous of issues with vehicle oil consumption knock knock sensor replace and other maintenance done since purchase vehicle brand new in 2018

ENGINE,FUEL/PROPULSION SYSTEM — Filed 09/23/2024

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.