2021 Hyundai Sonata Hybrid problems

Filed Sep 18, 2026 · Fuel system · AZ

The vehicle was brought to an authorized Hyundai dealer to have Service Campaign TBH and 94B completed. These campaigns were explicitly designed to prevent known mechanical defects (cracked EHRS assemblies and high-voltage battery errors). The software patches failed to protect the vehicle. The physical hardware has now catastrophically failed exactly as predicted by the campaign, resulting in extreme engine overheating and a physically swollen high-voltage battery pack. Hyundai is refusing to cover the cascading physical damage caused by their own failed campaign remedy, leaving me with an active safety and fire hazard. FUEL/PROPULSION SYSTEM" and explicitly state that the vehicle experienced an unchecked thermal event due to an ineffective corporate software update (Campaign TBH / 94B). All documents I have supporting this will not fit in this upload limit.

Filed Sep 18, 2026 · Fuel system, Transmission · VA

​My Lincoln Nautilus (~9,180 miles) logged 6 "Powertrain Malfunction / Reduced Power" alerts in the [XXX] telematics system between XXX (XXX at 7:59 PM and 8:16 PM; XXX at 1:07 PM and 1:39 PM; XXX at 11:16 PM; and XXX at 10:56 AM). Out of the 6 logged events, I experienced severe loss of motive power during two of them. On XXX, while driving 70 mph on I-95, the vehicle completely lost all propulsion. Coasting without power, I was unable to pull fully onto the shoulder, leaving the car partially stuck in active traffic and narrowly escaping a high-speed collision. Once stopped, the vehicle failed to recognize that it was in Park, causing the electronic parking brake to lock without releasing, which severely delayed towing recovery. The vehicle was towed to a Lincoln dealership in [XXX], whose service department was closed. Upon arrival, the vehicle suffered a complete electrical blackout; the key fob would not unlock the doors, requiring physical key entry. A sales representative provided a jump box, allowing me to start the car, drive back to [XXX], and deliver it to Cavalier Lincoln Ford in [XXX] between 5:00 PM and 7:00 PM on XXX. Cavalier Lincoln Ford stated they could not reproduce the malfunction. The vehicle and its electronic records remain available for inspection upon request. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Aug 5, 2026 · Electrical, Engine · MI

The vehicle experiences sudden, complete electrical power loss while driving at speed on highways and city streets or on the parking. All digital displays turn off, the engine shuts down, and power-assisted steering and braking are instantly lost without prior warning, presenting an extreme collision risk. The issue first occurred in August 2025 at approximately 48,000 miles and was taken to an authorized Hyundai dealer in Michigan for warranty repair. The dealer held the vehicle for over 30 days but failed to correct the defect. The identical power failure has continued and recently escalated to daily occurrences. A second Hyundai dealer (Pacifico Hyundai, Philadelphia, PA) diagnosed an intermittent open circuit in the engine wiring harness but Hyundai Motor America refuses to repair the vehicle under warranty, claiming 'outside influence' without providing evidence. Driving a hybrid vehicle that randomly cuts all power in live traffic is a life-threatening safety hazard. Hyundai Motor America has failed to rectify this critical safety defect.

Filed Jun 22, 2026 · Electrical · VA

I purchased this vehicle pre-owned approximately two years ago and have since developed concerns about its reliability, particularly related to the electrical and hybrid systems. In hindsight, I suspect these issues may be part of the reason the original owner traded it in to a CarMax dealer. Shortly after purchasing the vehicle, I began experiencing recurring problems with the 12V battery, including frequent instances requiring battery resets. Interestingly, these issues were significantly less frequent during colder weather. More recently, as temperatures have increased, the problem has worsened considerably. For about the past month, the vehicle loses power and dies immediately after each drive once the ignition is turned off. This situation escalated yesterday when the “Check Hybrid System” warning light signalled while I was driving on a busy road. I had not encountered this warning before, but after researching the issue, I discovered that other Hyundai hybrid owners have reported similar problems. In some cases, these issues have led to dangerous situations, including vehicles shutting off unexpectedly while driving at highway speeds. While I cannot determine the extent of this issue across all Hyundai hybrid vehicles, the frequency of similar reports suggests a systemic defect affecting at least a subset of Hyundai Sonata Hybrid models. Regardless of scale, these battery issues present a significant inconvenience and a serious potential safety concern. I am requesting a formal review of this issue and guidance on potential remedies or corrective action.

Filed May 22, 2026 · Electrical · OH

The vehicle’s 12-volt electrical system repeatedly loses power within about 1 hour of sitting. The car becomes completely unresponsive (cannot unlock or start) and requires use of the built-in 12V battery reset button to restore power. This occurs frequently and makes the vehicle unreliable and potentially unsafe, as the car may become inoperable without warning. This appears to be an electrical system defect or parasitic power drain. The issue has been ongoing.

Filed Apr 9, 2026 · Engine · FL

See attached document for complaint.

Filed Aug 11, 2025 · Electrical · SC

Owned car since 09/2024 with 64K miles. Battery system (12V/hybrid system) has shut down and died 47 times since 04/2025 - no shut downs before then. Car with ~69K miles at that time. Dealer had car six weeks (05/17 to 07/05/2025) and it died “a number” of times and report that Hyundai claims this is “what the car is supposed to do.” Since 07/05 it has died 12 times just sitting in my driveway or the lot at work. This is NOT normal. Internet blogs show DOZENS of other Hyundai hybrid owners reporting the exact same issue. Car now with 75K miles and under warranty. Dealer will not replace battery system.

Filed Jul 28, 2025 · Electrical · DE

This is on my 2021 Hyundai Sonata Hybrid Limited - for the 7th time the vehicle has been completely dead and unresponsive. I have had to gain entry to the vehicle using the manual key and press the "jump" button to get the vehicle to start. The Hyundai dealership ran a bunch of battery updates to the 12 volt battery several weeks ago and said that should hopefully fix the issue. Several weeks later on 07/19/2025 the vehicle was dead again. I had to use the key to manually gain entry and jump the car again. The dealership said that the 12 volt battery may need to be replaced and said that it is fully integrated with the hybrid battery system which is covered for 10 years/100K miles whichever comes first. I am still within the warranty period so hopefully Hyundai will fix the issue. From an online search, it appears this is not an uncommon issue with the Hyundai Sonata Hybrid. I am waiting on Hyundai for a fix and for .

Filed Jul 10, 2025 · Electrical · GA

What component or system failed or malfunctioned, and is it available for inspection upon request? RANDOM TOTAL ELECTRICAL FAILURE (DOORS WON'T UNLOCK, CAR UNRESPONSIVE) How was your safety or the safety of others put at risk? DIFFICULT TO GAIN MANUAL ENTRY TO CAR, PARTICULARLY IN DARK SITUATIONS Has the problem been reproduced or confirmed by a dealer or independent service center? NO, I HAVE TAKEN THE CAR IN FOR SERVICE TWICE AND THE ISSUE HAS NOT BEEN CORRECTED. THE CAR IS BACK AT THE DEALERSHIP NOW FOR A THIRD ATTEMPT. Has the vehicle or component been inspected by the manufacturer, police, insurance representatives or others? YES Were there any warning lamps, messages or other symptoms of the problem prior to the failure, and when did they first appear? NO As a reference: [XXX] Key Takeaways from the Thread: Several 2021 Hyundai Sonata Hybrid owners (and a few Ioniq and Elantra Hybrid owners) are reporting the exact same symptoms: Random total electrical failure (doors won’t unlock, car unresponsive) Requires manual key to enter 12V battery reset button inside vehicle restores power No error codes or permanent fixes from dealerships Issue occurs sporadically, making it difficult to replicate or diagnose Some dealers have replaced the 12V battery or DC-DC converter, but results are mixed No formal recall exists yet, despite growing reports INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Jun 30, 2025 · Electrical · CA

Every day the car is dead, have to take the manual key out pop door cover off unlock car manually push the 12v reset button and hold fob to start/stop button for car to work again. Happens daily.