2021 HYUNDAI SONATA HYBRID Electrical System Problems

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.

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...

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...

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.

12v battery dying randomly

the car randomly goes into dead or limp mode and unable to start. need to jump start it to come alive. No codes shown once its jumstarted. it has happened at random on several occasions.

When the vehicle is turned off the 12v Lithium battery will die. This is a intermittent occurrence that has happened approximately 7 times since [XXX]. Today is December 12, 2024. The car is currently at All Start Hyundai dealership in Pittsburg, CA. This dealership initially denied the car had a problem because they could not duplicate it in a 24 hour period and told me "the car is operating as designed". When I insisted they check the health of the battery, the service department would not do this until they received technical advise from Hyundai headquarters (HQ). It is a multistep process to get to the battery and requires removing the back seat. When HQ advised the battery check, the service department found the battery was swollen and needs to be replaced. I have found information on chat boards and YouTube where other car owners having the same issue. Why...

The BMS module within my cars hybrid system failed causing a parasitic drain on the hybrid battery. The dealership where the work was performed would have to be contacted for pictures. The hybrid battery system swole to a dangerously inflated level and did not produce any codes for an OBD reader to pickup. This has caused the dealership to turn my car away multiple times before finally performing the in depth inspecting required to verify battery swelling. This is a known problem throughout the internet I searched "2021 hyundai sonata hybrid battery dying every day" reddit has plenty of user with the same issues. I am not aware of who has inspected my battery besides the dealership. There was no warnings at all the only reason my battery was finally looked at is because of my persistence.

The contact owns a 2021 Hyundai Sonata Hybrid. The contact stated that the key fob was inoperable and after using the key to manually open the door. The contact stated that the vehicle failed to start while pressing the START/STOP button. The vehicle was towed to the local dealer, but the cause of the failure was not determined. The contact was advised that when the failure occurred, to start the vehicle, the battery reset button should be pressed before pressing the START/STOP button. The manufacturer was not contacted regarding the failure. The failure mileage was 24,000.

On three separate occasions over the last two months, while driving, an alert comes on that says check hybrid system then the vehicle powers off. When this happens, you lose the ability to accelerate break steer, and I have been lucky each of those three times and that I was in a situation where there was not much traffic. I am not able to drive the vehicle at this time. I have reported the problem to Hyundai and they want me to drive the vehicle to the dealership for another check of it. They have looked at it once before and have not been able to diagnose a problem. It is unsafe to drive and they are not willing to assist in getting the vehicle to the dealership without me getting it over there.

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...

My battery has died twice, so dead that I can’t even unlock to car with the remote. The first time I had it jumped and took it to the dealership where they were unable to find anything wrong with it and they told me if it happened again to have it towed in so they could diagnose it while the battery was dead. So that happened again and I had it towed in to the dealership in early April. It’s now July and they still have my car and don’t have a diagnosis yet. They have had their field engineers out to run all sorts of tests, but nothing yet. Today they told me they have 3 Sonata hybrids there with the same issue as mine.

Randomly the car will get a message when driving starting “ Check Hybrid system. Turn engine Off” and the car isn’t able to accelerate when this happens. When you cut the engine off the car is unable to start again until it is jumped. I’ve confirmed the battery isn’t the issue however something with the vehicle is wrong. There are many accounts of people online dealing with the same issue.

Driving on the freeway when we got a notice on the dash that we needed to pull over and the vehicle shut down due to a fuse,/battery issue.

My car will power off randomly, or will seem as though there is no power. I have to revert back to the manual key to enter the vehicle and hit the 12vlt reset to power it back on. This happened at least 3 times. Once while operating the vehicle, and twice while the vehicle was left parked. This is not a low battery issue as, the car will only do this occasionally, and not every time I enter and turn on the vehicle. There is no error code to follow this mishap as all power goes out and the dealer maintenance has nothing to work with.

Integrated 12v battery in hybrid system keep draining out. I have to manually open the car and reset it every time in order to be able to drive.

The Battery dies randomly and requires the physical key to unlock the door. It is a hybrid, so it has a 12 volt battery button that jumpstarts the car. While driving the vehicle, the battery meter on the dashboard will show a near-full battery and then a near-empty battery within a few minutes. This vehicle was bought brand new from a Hyundai dealership and for the first 2 years, there wasn't an issue. The past few months, the battery issue started.

the car keeps randomly dying (not during driving "yet") it happens at least once or twice a week of where i go to ride my car and it is completely dead, i have to unlock the door using the key fob manually and push the "Reset 12v battery button" inside the car. i have tried to have Hyundai service repair the issue or at least tell me what's wrong but no hope as they can never replicate the problem. I am seeing alot of users posting online on numerous web forms (reddit,facebook..etc) that they are having the same exact issue as me for the same exact model of my car, With also no help from the dealer on the matter. This must be a defect at some point and would greatly appreciate if NHTSA can help push this issue to the dealer

The Battery dies randomly (like I have to open the car with they physical key to access the car dead) there isn't a pattern. I have taken it to the dealership and they can't diagnose it because they cant replicate the issue and say nothing is wrong. Sometimes the car dies while I'm INSIDE and just having lunch while the car is off.

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...

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...

On Wednesday, October 6th, I was driving full speed (65mph) on a major highway. Multiple lights on the dashboard came on. The LCD display screen for music, apps, etc. went black. More lights came on and others went off on the dash display. I let off the accelerator and steered the car. The fuel efficiency was wilding jumping back and forth. Soon enough, all the lights went back off, but the mileage gauge (fuel efficiency) continued to jump wildly. The brakes seemed to respond differently- almost as if there was a delay between me pressing the brake and the brakes catching. When I needed to accelerate, the car seemed to be having trouble switching between the electric and gas motors. I was able to drive to a safe location and shut the car off. This was terrifying, as the car's computer system or electrical system clearly failed, even if temporarily....