2017 Hyundai Sonata PLUG-IN Hybrid

I am reporting a serious safety issue involving a 2017 Hyundai Sonata Plug-in Hybrid (VIN: [XXX] ), originally purchased in California. While driving at approximately 70 mph on a highway, the vehicle suddenly lost all propulsion without warning and rapidly decelerated. This created a dangerous situation with surrounding traffic and put me and my family at risk. I had to quickly maneuver to the shoulder to avoid a potential collision. The vehicle was towed to an authorized Hyundai dealership in Utah, where it was diagnosed with a failure of the high-voltage battery system. I was informed that the battery requires replacement. This type of sudden loss of propulsion at highway speed is extremely hazardous and could result in a crash, injury, or fatality. There were no prior warnings indicating an imminent failure of this severity. Given the safety risk associated with unexpected loss of propulsion, I am concerned this may represent a broader issue affecting similar vehicles. The vehicle is equipped with an interior camera, and video of the incident can be provided if needed. I respectfully request that this issue be investigated as a potential safety defect. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

To the National Highway Traffic Safety Administration, I am filing this formal safety complaint regarding a dangerous engine failure incident involving my 2017 Hyundai Sonata Plug-in Hybrid. Description of Incident: While traveling on CA-85 near Mountain View, California, at approximately 65 miles per hour, the engine suddenly and without warning lost all power. The vehicle began to slow down involuntarily in active highway traffic, creating an immediate and serious risk of rear-end collision. The driver had no ability to maintain safe highway speed or accelerate out of danger. The vehicle had to be towed from the scene to the dealership. There was no warning light or prior indication that engine failure was imminent. The failure was sudden, complete, and occurred at highway speed in heavy traffic conditions. Safety Risk to the Public: This incident represents a significant and ongoing public safety hazard. A sudden, unpredictable loss of engine power at highway speed — with no prior warning — places the driver, passengers, and surrounding vehicles at serious risk of collision. This is not an isolated mechanical inconvenience; it is a life-threatening failure mode. Known and Documented Defects: The 2017 Hyundai Sonata Plug-in Hybrid has been the subject of multiple recalls and class action litigation related to engine defects. My incident is consistent with the known failure patterns documented in those proceedings. Despite this history, Hyundai Motor America has denied my warranty claim, citing missed services — a characterization I dispute, as the vehicle was serviced exclusively at an authorized Hyundai dealership whenever the onboard system indicated service was due, and no technician ever identified or disclosed any engine damage during those visits. Request to NHTSA: I respectfully request that NHTSA: 1. Open or expand an investigation into engine failure incidents in the 2018 Hyundai Sonata Plug-in Hybrid 2. Investigate whether a recall is warranted

While driving at a high rate of speed propulsion to the vehicle suddenly and without warning ceased, the electric and internal combustion engine were non-responsive (ICE stopped; hybrid motor didn't provide propulsion), the warning light said "Check Hybrid System. Turn off engine" I was put at risk because I was traveling at highway speed and was given no warning before the vehicle shut down. This has occurred nine times, I've reported all to Hyundai, they have had the car in the shop three times, the issue is not fixed. No, despite ODB2 error codes, the car has not shut down while a dealership is driving it. Yes, the vehicle has been inspected multiple times by Hyundai. Yes, always "Check Hybrid System. Turn off engine", in almost all cases the check engine light comes on after that, and in some cases additional lights such as "auto hold". This first occurred in Dec 2023, I was told the car was fixed (it wasn't) and happened again in October 2024. I haven't been able to drive my car since then.

Occurrence: This has been a recurring issue for over a year (over a year, might be closer to two years now) for our PHEV Sonata. It has happened approximately 10 times. Problem: Total engine shutdown when driving the car. "Shut down engine" type error message pops up and cannot accelerate. Steering still works, but it can be hard to pull over due to lack of engine power. The car can be restarted after shutting down, but must first come to a complete stop and into Park. Safety Issue: The car stops working. Obviously, this would be quite dangerous on a busy road, a highway, or if you were taking a left turn, etc. Confirmation: The dealer indicates that the hybrid battery is a problem and should be replaced. However, due to supply chain issues, we have been waiting for over a year for the replacement. **** Reproduction Steps: **** We have found that it is most likely to happen with a fully charged battery and a sudden braking action. I suspect the issue happens when trying to charge the battery but due to its condition, it shuts down instead. It tends to happen: 1) Full Charge: Battery is fully charged overnight or "topped up" to full charge 2) Sudden Braking: Having to brake hard, such as being cut off. We have found that adjusting charging and driving habits has reduced but not eliminated the issue. Suggestion: I would suspect that having some electrical component to prevent a sudden overcharge might eliminate this problem (shunting excess current or turning off regenerative braking for sudden stops). Warning Messages: A warning message is seen, but it happens at the same time the engine is shut down and disappears before you could take a picture of it (as you are busy trying to do an emergency pull over).

Problem began Dec. 2021. Has occurred on 16 occasions since then. Warning light "Check Hybrid System; Turn off Engine" comes on while driving. The car then shuts off the engine and there is a 100% loss of motive power. Sometimes is associated with very rough braking with the car "knocking'." On 3 occasions there has been partial/near complete loss of braking power. All incidents have occurred while under power, so far all while under 45 mph. No accidents yet. Two near collisions from the rear. Hyundai was notified of the problem Dec. 2021/Jan. 2022. After a month of testing they stated the car needed a new plug-in hybrid battery. One was not available and due to "supply chain issues" is still not available 15 months later. Dealership provided a loaner vehicle Jan to Sept. 2022. They requested their car back and Hyundai initially agreed to cover the cost of a rental car. I rented a car for 6 weeks in Sept.-Oct. 2022 at which point a new case manager informed me that Hyundai would not pay for a rental vehicle any longer (note: they did reimburse me the cost of those 6 weeks rental). Hyundai is well aware of the safety issues involved in driving this vehicle. However, they have chosen to ignore them. Their attorney, in a letter to the Ohio Attorney General's Office, blamed the lack of a plug in hybrid battery on supply chain issues (letter was Nov. 2022, at which time the battery was supposed to be available March 2023) and only stated that my vehicle was "drivable." Another warning message "High System Temperature; Switching to Hybrid Mode" has been occurring for a couple of years periodically. Since October 2022, the malfunction indicator lamp is always on and 99% of the time the "Check Hybrid System!" warning light also comes on after about a minute after starting the vehicle. On 3 other occasions the vehicle has entered into "limp home mode" instead of complete shutdown.

The engine started knocking on the freeway and all the lights in the car went off. The engine failed and I barely made it off the freeway. I was almost hit by two cars trying to get to a safe place. The engine has the same issue as the other morsels that have recalled the engine for the same rod failure issue but Hyundai has not extended the recall to the plug in hybrid. This model also bends to be recalled because it is a danger to all owners and other drivers. Hyundai declined to repair the defective engine.

On cold mornings, during the first start of the day, and while going downhill, the internal combustion engine comes on while running on electrical power from the battery. This is understandably to heat up the engine to ideal temperatures. But within a minute, the car gives a hybrid battery error, fully loses power requiring to be stopped immediately. This is obviously dangerous anywhere but particularly downhill. The car requires to be restarted after pulling over 1-3 times until the engine / battery reach ideal temperatures. Then the car runs as expected. The dealership has been unable to diagnose the issue and chalked it up to an unrelated recall - which has been fixed, but the issue still occurs risking the safety of the people inside the car and around.

While driving on surface streets (10-15 MPH) about 5 minutes out from our house, the accelerator stopped working properly and a warning popped up along the lines of "Hybrid HEV warning: Please shut off engine and restart." Since there were no other cars behind us, we were able to thankfully pull over without too much trouble. However, if we had been on a highway this would have been incredibly dangerous, as we would have lost speed quickly and had no safe way to pull over. There were no warnings prior to this happening on that day. The car just sudden stopped working and then lights popped on. Using an OBD reader, the issue code was P0DE7: Hybrid/EV Battery - Cell Voltage High. We are going to the dealer at the earliest appointment to have it looked at, and the car is clearly not safe for anything but surface roads with easy pull-offs. Related Items: A week or so ago, we had an incident where the car was a bit sluggish to accelerate after a right hand turn (e.g., needed to take foot off the gas, then put it back on after a moment to accelerate). However, no check engine light came on and the car ran fine after. A second potential related item was that the expected mileage on battery-only had reduced from about 27 to 23 miles on a full charge. This occurred within the last two months before this issue.

The contact owns a 2017 HYUNDAI Sonata Plug-In Hybrid. The contact stated while driving approximately 35 MPH, the vehicle started making a loud knocking sound. The contact pulled over and noticed an excessive amount of oil underneath the front of the vehicle. The contact took the vehicle to a certified mechanic who diagnosed that there was a hole in the engine block. The mechanic showed the contact a piece of metal that had fractured from the engine. The contact stated that three days later while driving approximately 25 MPH, the vehicle stalled. The vehicle was towed to the dealer who confirmed that the vehicle was not included in NHTSA Campaign Number: 21V727000 (Engine). The vehicle had not been repaired. The manufacturer was made aware of the failure. The approximate failure mileage was 76,000.