2021 Hyundai Sonata Hybrid Problems

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.

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.

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.

See attached document for complaint.

While driving, engine alerted that it was overheating. Pulled over and coolant was very low, so I refilled it and then while driving to my family's garage to use the lift, saw white exhaust smoke. Took it to an independent mechanic, and in the ~10 mile trip there, over a quart of coolant had been burned off. He was able to reproduce the issue. No issues with the engine operation, it runs well and efficient, no check engine light. Mechanic found that a coolant line runs to the middle of the exhaust system and that this seems to be the issue. Other owners seem to have reported this same issue with this same model and roughly the same year, in which the muffler assembly needs replaced due to coolant leaking into the exhaust. Only prior issue was less warm air out of the vents for the previous week or so, but no other issues or warnings.

My 2021 Sonata Hybrid Limited has been in the shop for over 3 months. At least 4 times while driving on city streets, I'd receive an error stating problem with hybrid system please turn off vehicle. Car would go into limp mode giving me just enough power to pull off to the side of the road (if possible), then completely shutdown. Fix action is to hit jumpstart button to get the power back to the vehicle in order to power it on again. After those issues battery constantly died and I had to use the physical key to open the door and hit the jumpstart button to get power. Dealer (Hyundai Jim Click East, Tucson, AZ) couldn't find an issue initially stating they could not replicate what I was experiencing. But eventually my patience ran thin and they finally identified a voltage error while in the service department. The rep informed me that the issue lies with the 12v battery which is integrated into the hybrid battery (stupid design). Service tech had to order a 12v battery from Korea (after dismantling the hybrid battery and sending the pics to Hyundai for approval). This was [XXX]. Still waiting on the parts, no updates at this time. There was another sonata hybrid limited like mine also at the dealership for the same issue. This vehicle had been there since June. They were able to get a new battery for that vehicle, however after a week the same issues reoccurred. I've noticed on Reddit forums that many 2021-2022 sonata hybrid limited owners have been experiencing the same issue, with the same long wait times from Hyundai HQ regarding a solution. At this point I believe it'd be best to open an investigation as there it's been difficult for the dealership and the owners to get any answers from Hyundai regarding this issue. I'd also suggest a recall for this vehicle as it's clearly a widespread problem and hopefully that will give Hyundai the kick in the ass needed to actually take this seriously. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

On three separate occasions, while going very fast (60-78 mph), the automatic emergency braking system turns on. The warning lights flash and there is some type of warning noise. I don't even know if it starts to break because it scares me so much, I just press the gas. It turns off within a couple of seconds, but that is not the point. If I didn't react so fast, I am unsure of what could actually happen.

The vehicle has been turning completely off after use for over a year now. At first it would happen every now and then at the beginning and all you'd have to do was restart the car manually. Now every time the car is turned off it needs to be restarted manually now. The car will also shut itself off while you are driving. It will tell you something is wrong and then won't let you get over 15-20 MPH. If you are on a neighborhood, it's less dangerous for this to happen where you can pull over and turn off the car and restart it. But I have seen other post that they've started to malfunction on the freeway and highways before. My car is a 2021, but recently I've seen 2023 models are doing this as well. I know some people on the internet have gotten their car fixed by replacing a back logged battery. It took some people over a year to get it diagnosed correctly and 6 more months to get a new battery. I assume this is also what is wrong with my vehicle. It is in the shop right now, but we have not gotten an answer back even htough it's been there for 10 days. The car app has also indicated that the car has not been turned on since we left it there.

Battery keeps dying randomly. Approximately once every other week and I drive 12k miles a year… dealership reassures me it’s find. Found numerous reports of other Sonota Hybrid users experiencing a similar issue.

When I arrived in the parking lot and selected the R (reverse), the vehicle stayed in the D (Drive) although that it was moving backwards and was able to park it. The shift selector was stuck in DRIVE (Drive) leaving the vehicle on but not operational. After several attempts to allow the vehicle to cool and the battery to reset, (30 minutes_ later), the car started and took the vehicle to be serviced. The vehicle technician said they had a difficult time diagnosing the vehicle because it was giving different codes. They said that while testing they found the Transmission Shift Selector Module was damaged. Not physically but electronically damaged. They also stated that the car could have other problems but that they needed to replace the module first because it could be the cause of the other errors.

The vehicle, after parking, is nonresponsive to the key fob, nor will it start. This can happen at anytime and anywhere. Dealer said "It is possible the integrated 12v battery into the hybrid battery may be faulty. No codes or tests can confirm the issue. The dealer said the key fobs tested ok." My wife works late at night in a dark area, this has happened 2 times at her place of work and we are concerned for her safety as she has to wait outside for a tow truck to tow it to the dealer. The first 3 times it occured, this issue started around march of 2024, and repeated every 30-45 days. Now it has happened 2 more times in the last week. No warning lamps or indications of problems. The windshield has distortion within the glass and is not a clear view. It is as though you are looking through the heat of a jet engine trying to focus on what is on the other side. This is a major distraction while driving, reading the heads up display in the car, reading street signs and general navigation of pedestrian and other vehicle traffic. There is no aftermarket film or materials on the windshield. The door handle on the drivers side has a cover plate over the hole where a manual key could be inserted. As a construction worker I have very strong hands and I have a difficult time removing the cover plate. The last time I removed the plate I cut my hand on the interior part of the handle as the cover plate popped off. That is how hard the plate is to remove. My wife cannot remove the cover plate on her own. This system is in place for the manual use of the hidden key inside the key fob to be able to open the door in the event of a power failure of the vehicle. which has now happened randomly 5 times.

215/55R17 94V BSW. . Contacted Michelin about two (2) of the four (4) tires DO Not have the date of manufacture on side wall. These tires are direction specific. They should known that. Maybe the date of manufacture is on the inside wall but they should known the the tire is DIRECTIONAL and be on Both sides. I am not going to jack up my vehicle and remove the tire to check the code (IF it is only on one sidewall). Will Return tires to Costco where purchased. Michelin has not responded to my emails...

The vehicle, after parking, is nonresponsive to the key fob, nor will it start. This can happen at anytime and anywhere. Dealer said "It is possible the integrated 12v battery into the hybrid battery may be faulty. No codes or tests can confirm the issue. The dealer said the key fobs tested ok." My wife works late at night in a dark area, this has happened 2 times at her place of work and we are concerned for her safety as she has to wait outside for a tow truck to tow it to the dealer. The first 3 times it occured, this issue started around march of 2024, and repeated every 30-45 days. Now it has happened 2 more times in the last week. No warning lamps or indications of problems. The windshield has distortion within the glass and is not a clear view. It is as though you are looking through the heat of a jet engine trying to focus on what is on the other side. This is a major distraction while driving, reading the heads up display in the car, reading street signs and general navigation of pedestrian and other vehicle traffic. There is no aftermarket film or materials on the windshield. The door handle on the drivers side has a cover plate over the hole where a manual key could be inserted. As a construction worker I have very strong hands and I have a difficult time removing the cover plate. The last time I removed the plate I cut my hand on the interior part of the handle as the cover plate popped off. That is how hard the plate is to remove. My wife cannot remove the cover plate on her own. This system is in place for the manual use of the hidden key inside the key fob to be able to open the door in the event of a power failure of the vehicle. which has now happened randomly 5 times.