2017 Hyundai Sonata Plug-In Hybrid Engine Problems

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)

NHTSA ID

11734703

Incident

Apr 11, 2026

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

NHTSA ID

11725213

Incident

Dec 7, 2025

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.

NHTSA ID

11648675

Incident

Oct 23, 2024

Vehicle lost power in freeway. Complete power failure. Early crashed into. Vehicle coasted to off ramp and towed away.

NHTSA ID

11567254

Incident

Nov 27, 2023

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).

NHTSA ID

11520782

Incident

Apr 13, 2023

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.

NHTSA ID

11516024

Incident

Dec 22, 2021

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.

NHTSA ID

11454311

Incident

Aug 5, 2021

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.

NHTSA ID

11451054

Incident

Feb 7, 2022

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.

NHTSA ID

11450701

Incident

Feb 6, 2022

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.

NHTSA ID

11434553

Incident

Sep 23, 2021

Mileage

76,000 mi

On August 31st 2021, While driving my 2017 Hyundai Sonata PHEV on interstate 95 the check engine and hybrid system warning lights came on and the car simultaneously lost power for 3-4 seconds, which caused a decrease in speed from 65 to approximately 50 mph. There was a tractor trailer behind me but thankfully it braked to avoid striking my car. The car regained partial power and I was able to drive it home. I took the car to the dealership to have it repaired. The dealer diagnosed a faulty battery management system, and replaced this component after 17 days. On September 25, while driving on a street the car once again lost power for 3-4 seconds, with the check engine and hybrid system lights simultaneously illuminated. There was a recall on my vehicle several years ago to prevent this dangerous problem. I had the car repaired at that time but clearly the problem was not fixed as my car has subsequently lost power on two separate occasions, in a manner that could have easily caused a crash.

NHTSA ID

11434360

Incident

Aug 31, 2021

TL* THE CONTACT OWNS A 2017 HYUNDAI SONATA PLUGIN HYBRID. THE CONTACT STATED WHILE DRIVING 50 MPH, SHE HEARD AN ABNORMAL SOUND. THE CONTACT STATED THAT THERE WAS NO WARNING LIGHT ILLUMINATED. THE CONTACT DROVE TO HER RESIDENCE. THE CONTACT STATED SHE HAD THE VEHICLE TOWED TO HARRISONBURG FORD, INC. (3155 S MAIN ST, HARRISONBURG, VA 22801; (540) 434-0700), WHERE IT WAS DIAGNOSED WITH NEEDING THE ENGINE TO BE REPLACED. THE VEHICLE WAS REPAIRED. THE MANUFACTURER HAD NOT BEEN INFORMED OF FAILURE. THE FAILURE MILEAGE WAS APPROXIMATELY 75,000.*DT

NHTSA ID

11377893

Incident

Sep 4, 2020

Mileage

75,000 mi

I WAS DRIVING MY HYUNDAI 2017 SONATA PLUGIN HYBRID ON THE HIGH WAY IN HEV MODE AND SUDDENLY I FELT SEVERE VIBRATION IN MY CAR. THEN I CHANGED MY ENGINE TO EV MODE AND IT WAS FINE. ENGINE LIGHT CAME ON. EVERY TIME THE GAS ENGINE CAME ON THE CAR STARTED VIBRATING AND NON RESPONSIVE TO GAS. I DROVE ABOUT 10 MORE KM TOWARDS HOME ON ELECTRIC ONLY ENGINE AND THEN GOT IT TOWED TO THE DEALERSHIP. IT FELT LIKE ENGINE LOST ITS POWER. I RECENTLY CHANGED THE VOLTAGE PROTECTION DEVICE ON THE CAR AS A RECALL. ALL SERVICES WERE DONE ON TIME AND CAR HAD ONLY 33000 KM.

NHTSA ID

11210126

Incident

May 26, 2019

Mileage

33,250 mi

THIS IS MY FIRST TIME BUYING A BRAND NEW CAR IN MY MID 40'S. I PURCHASED THE CAR (PLUG IN HYBRID) WITH ONLY 25 MILES ON MARCH 15, 2018 AND AFTER 7 DAYS AND 353 MILES LATER, UPON DRIVING AND COMING TO A STOP IN THE CITY OF PHILADELPHIA, PA, THE CAR STALLED AND LOST POWER. WARNING MESSAGE "CHECK HYBRID SYSTEM." I HAD TO STEP ON THE GAS PEDAL ALL THE WAY DOWN TO THE FLOOR AND WAITED A SECOND OR TWO IN ORDER FOR IT TO MOVE AT A TURTLE'S PACE. FORTUNATELY, I WAS ABLE TO FIND A SAFE SPOT TO PARK THE CAR. IT WAS TOWED TO A LOCAL HYUNDAI DEALERSHIP NEAR ME AND AS OF YESTERDAY, 3/27, NO DIAGNOSTIC FINDINGS. I HAVE NOTIFIED HYUNDAI MOTOR AMERICA AND THEY HAVE OPENED A CASE#. I HAVE ALSO REACHED OUT TO THE SELLING DEALER TO HELP ME WITH THIS MATTER. THIS IS EXTREMELY UPSETTING AND DISAPPOINTING, ESPECIALLY FOR ME AS NEW CAR BUYER!!!

NHTSA ID

11081789

Incident

Mar 22, 2018

Mileage

353 mi

14 MARCH 2018 10:30 AM, 70 MPH ON US 101 TO SAN FRANCISCO, HEV MODE, RAINY WEATHER, 4 PASSENGERS FOR A BUSINESS MEETING. CAR STEERING SHUDDERED AS IF THE TIRES SLIPPED AND SPUN ON THE WET PAVEMENT. ESC, BRAKE, AND AUTO HOLD LIGHTS TURNED YELLOW. WAS ABLE TO DRIVE THE CAR NORMALLY TO REACH DESTINATION, PARKED, ATTENDED MEETING, AND STARTED DRIVING BACK HOME WITH MY PASSENGERS AT 3PM. ESC, BRAKE, AND AUTO HOLD LIGHTS WERE STILL ON. HEV MODE. 30 MINUTES LATER, I-280 AT 65+ MPH, ENGINE POWER DRASTICALLY REDUCED ABRUPTLY, CAR STARTED TO SLOW DOWN AND BECAME UNRESPONSIVE TO THE GAS. TURNED ON EMERGENCY FLASHERS AND WITH GREAT DIFFICULTY IN THE EVENING RUSH HOUR COMMUTE TRAFFIC, MANAGED TO SHIFT RIGHT THREE LANES AND TAKE THE NEXT EXIT, WENT INTO A PARKING LOT AND STOPPED THE CAR. CONSULTED MANUAL FOR ANY MEANINGFUL ACTIONS. STARTED CAR BACK UP. MIL LIGHT ALSO CAME ON ALONG WITH MESSAGE TO TAKE CAR TO DEALER. RAN VEHICLE DIAGNOSTICS AND GOT 'A POSSIBLE CONDITION WITH THE ECS HAS BEEN DETECTED AND A FULL SYSTEM CHECK IS RECOMMENDED SOON'. STARTED DRIVING CAR AGAIN. SAME LACK OF ENGINE POWER. DROVE THROUGH LOCAL ROADS AND COUNTLESS MANY TRAFFIC LIGHTS AND REACHED HOME AFTER 4 HOURS (NORMAL = 1 1/2 HOURS). AT HOME, PLUGGED CAR IN FOR CHARGING. CHARGING STARTED NORMALLY. AROUND 10PM, WANTED TO TAKE A PICTURE OF ALL THE LIGHTS, SO PULLED CHARGING CABLE OUT AND STARTED CAR. ALL LIGHTS WERE OFF EXCEPT MIL! DECIDED TO TEST DRIVE AND FOUND NO LOSS OF POWER. TOOK IT TO NEARBY FREEWAY, FLOORED GAS PEDAL. CAR RESPONDED WITH FULL POWER! NEXT DAY MORNING, DRIVING CAR TO DEALER, HEV LIGHT AND CONTINUOUS WARNING BEEP CAME ON, JUST A MILE AWAY FROM HOME.

NHTSA ID

11079939

Incident

Mar 14, 2018

Mileage

12,470 mi

ON 3/15/2017 AROUND 8AM, I STARTED MY CAR TO LEAVE FOR WORK AND THE CAR SHOWED A WARNING "CHECK HYBRID SYSTEM" AND THE CORRESPONDING WARNING LIGHT CAME ON. THE GASOLINE ENGINE ALSO STARTED RIGHT AWAY AND STAYED ON, EVEN THOUGH THE EV BATTERY WAS FULL. THE ENGINE REMAINED ON THROUGHOUT MY COMMUTE TO WORK AND BACK TO HOME IN THE EVENING. I PLUGGED THE CAR IN MY GARAGE FOR CHARGING OVERNIGHT WITH THE TIMER SET TO START THE CHARGING AT 10PM. AROUND 10:45PM, MY WIFE AND I OPENED THE INTERNAL GARAGE DOOR FROM INSIDE THE HOUSE AND IMMEDIATELY SMELLED EXHAUST FUMES AND HEARD THE ENGINE RUNNING. I OPENED THE GARAGE OVERHEAD DOOR RIGHT AWAY AND UNPLUGGED THE CHARGING CABLE WHICH TURNED THE ENGINE OFF. JUST TO BE SURE, I PLUGGED THE CABLE IN AGAIN AND TURNED OFF THE TIMER TO RESTART THE CHARGING IMMEDIATELY. AS SOON AS THE CHARGING STARTED, THE ENGINE CAME ON AND AFTER A FEW SECONDS STARTED REVVING UP ALSO. I IMMEDIATELY UNPLUGGED THE CHARGING CABLE AND ENGINE STOPPED. I TOOK THE CAR TO THE DEALER TODAY AND AM WAITING TO HEAR BACK FROM THE DEALER. I THINK THIS IS A POTENTIALLY SERIOUS SAFETY ISSUE AND HENCE I AM REPORTING IT.

NHTSA ID

10966358

Incident

Mar 15, 2017

Mileage

2,900 mi

FIRST EXTENDED DRIVE OF NEW CAR, CHECK ENGINE LIGHT CAME ON. TOOK IT TO DEALER FOR SERVICE, WAS TOLD I HAD "BAD FUEL" THAT THEY TESTED A SAMPLE AND FOUND E85 (ETHANOL) IN IT, WHICH IS NOT COVERED BY HYUNDAI NEW CAR WARRANTY FOR PLUG-IN HYBRID ELECTRIC VEHICLES. I PAID $828 TO HAVE FUEL DRAINED AND REPLACED, FUEL INJECTION CLEANING, AND DECARBONIZING AND THROTTLE BODY CLEANING. CHECK ENGINE LIGHT WENT AWAY, BUT TURNED BACK ON A FEW DAYS LATER. AGAIN TOOK IT TO DEALER BUT THEY WERE UNABLE TO GET IT TO TURN ON AFTER I LEFT IT, SO RETURNED THE CAR TO ME, NO CHARGE. I HAD ONLY ADDED 87 OCTANE GASOLINE (PER OWNER'S MANUAL RECOMMENDATION) TO MY CAR 3 TIMES PRIOR TO THE FIRST CHECK ENGINE LIGHT EPISODE, AT STATIONS THAT DID NOT SELL E85. DURING SUBSEQUENT CONVERSATION WITH HYUNDAI REP, WAS TOLD MAYBE WATER WAS IN GAS. BUT ENGINE RAN FINE AND I DROVE 100 MILES AFTER LAST GAS FILLUP SO I SUSPECT THERE MAY BE A PROBLEM WITH THE EMISSIONS SENSOR THAT MANIFESTS AS CHECK ENGINE LIGHT WITH RANDOM (INACCURATE) DIAGNOSTIC CODE. I GOT THIS CAR IN CHICAGO, BUT ILLINOIS IS NOT A LOW EMISSIONS VEHICLE STATE, SO THE PLUG-IN HYBRID IS NOT ALLOCATED TO HYUNDAI DEALERS IN ILLINOIS. THE SONATA HYBRID, HOWEVER, IS SOLD HERE BUT I DON'T KNOW IF IT SHARES THE SAME ENGINE/EMISSIONS SENSING SYSTEM AS MY PLUG-IN HYBRID ELECTRIC. DEALER SERVICE DID CHECK FOR OBVIOUS THINGS: GAS CAP, RESETTING THE ENGINE DIAGNOSTIC CHIP. I UNDERSTAND THE 2016 MODEL PHEV IS SUBSTANTIALLY THE SAME AS MY 2017 MODEL, IN CASE SIMILAR CHECK ENGINE LIGHT ISSUE HAPPENED WITH 2016 CARS.

NHTSA ID

10938754

Incident

Dec 10, 2016

Mileage

1,858 mi