general problems of the 2021 Hyundai Sonata - part 1

The internal core of the exhaust heat recovery system (ehrs), part of the center muffler/front pipe assembly (#28600-l5210), suffered a catastrophic failure. This allowed approximately 9 gallons of engine coolant to leak directly into the hot exhaust stream. Safety risk: this failure creates a severe visibility hazard. During acceleration from stop lights and stop signs, the vehicle emits massive, thick clouds of white glycol smoke. The smoke is so dense that it completely obscures the driver's view of trailing vehicles and prevents following drivers from seeing the roadway or my vehicle's brake lights, creating a high risk of rear-end collisions. Additionally, the rapid loss of coolant caused the engine to overheat and lose power while in motion, nearly causing a stall in active traffic. Confirmation: the failure was confirmed by the service department at washington Hyundai (invoice #174281). This is the second failure of this specific component (previously failed in Jan 2025). The manufacturer issued TSB 23-em-009h for this defect, acknowledging it affects 2020-2023 Sonata hybrids, but no safety recall has been issued. Symptoms: the issue was preceded by a "sweet" burning smell and a sudden "engine overheating" warning on the dashboard. The failed component has been replaced by the dealer, but the manufacturer refused to replace the coolant-poisoned oxygen (O2) sensors, leaving the vehicle in a technically compromised state. The failed unit is likely held by the dealer for warranty parts return.

Vehicle suddenly lost heat in 30 degree weather. No warnings, check engine light, or temperature gauge indicators came on. Lucky made it to a parts store and found out I was extremely low on coolant. Bought coolant and put it in. Made it back to the house and was immediately low again. No visible leaking. Oil was completely fine (1 gallon of coolant would have have left some kind indicator). Realized it was more than likely the ehrs. If this happened during the summer, my engine could have blown due to a poor design causing a major accident.

The ehrs coolant system failed and had a leak causing the coolant to be excessively burned off as thick white smoke. This caused me to not be able to see anything behind me and forced others to stop or slow down dramatically to avoid colliding with me. I had my engine overheat and force me to pull over on the side of an unsafe road because the exhaust system burned off my entire tank of coolant in less than a mile. I have taken this to a Hyundai dealership and they confirmed it was the ehrs system failure and told me it was a fairly known issue with the 2020-2023 Sonata hybrids. I was told that even if I get it replaced the possibility of having it happen again are pretty high. This seems extremely unsafe to myself and others.

P0471 code before 55k miles even after repair is made.

On I believe 1/14/26, my check engine light came on. Scheduled appt. For 1/16/26 for diagnostic. Several things were wrong. I decided to come back due to not having the money at the time. Over the wked, I remembered a recall notice I received around November that I asked about in November during my oil change & was told the parts aren't in & they'd give me a call. Upon viewing the recall it seemed some things I was told on 1/16/26 could be a result of the recall. I called my service person linda on 1/20/26, she spoke to her supervisor & they informed me some of the issues seem to stem from the recall. Linda gave me the manufacturer recall contact information. I contacted them on 1/20/26. She explained there was indeed a recall, there wasn't a remedy yet, it was safe to drive & if something changes, to call back. On 1/28/26 around 5:30am I left home for work & my car all of a sudden experienced a loss of power. It wouldn't go past 30mph. I returned back home & called out of work. I called the manufacturer recall & informed them. She made an appt. To take my car in the follow day, 1/29/26. I decided to drop it off that same day, 1/28/26. I had someone follow me being I could only go 30mph on a flat road & 10mph on a slight hill. I found out my service person linda was no longer employeed there. I spoke with another employee. He said they would have to do another diagnostic. I left my car. I called the dealership on 1/29/26 for an update, they had not looked at my car. I called the manufacturer recall, they assigned a case manger to my case. Jay from the nca, called me on 1/30/26 I believe. We've communicated several times without me receiving a adequate update. He's saying the issue seems to be steamed from the recall, there is now remedy yet, & they are still investigating. I've been without a car since 1/28/26, still making payments, missing work, haven't been offered a loaner & have no idea when or if I will get my car back.

I was driving my 2021 Hyundai Sonata at approximately 3:00 am when the vehicle suddenly began shaking and vibrating. While stopped at a traffic light, the check engine light illuminated, and the engine was shaking severely. I immediately pulled over and shut off the engine. After waiting approximately one hour, I restarted the vehicle, but it was only able to drive very slowly. The following day, the vehicle was towed to a local repair shop. Diagnostic testing showed a cylinder 3 misfire, along with evap system errors and faulty fuel injector issues. This failure occurred without warning and created a potential safety risk while driving. I am concerned this may be related to a defective fuel system.

Engine makes rattling and knocking noises. Transmission hesitates and jerks suspension front struts and rear shocks are bad. Possible the isolators. Having horrible back pain when riding in car. Starter intermittently doesn't work lane keep assistance goes over small bump in road will make car drive in opposite lane into on coming traffic. Took car to tameron Hyundai in birmingham on the 29th of December 2025. Told them everything thats going on with the car. They did nothing about any of the issues. Car has 55,000 miles on it as that is when all problems have incurred. 60000 mile warranty expires in February of this year.

The vehicle's hvac (heating) system failed. It stopped producing heat on one side of the vehicle. My mechanic/dealer diagnosed the issue as a broken component within the hvac case under the dashboard, requiring full dashboard removal and a repair estimated at over $3,000. This failure prevents the defroster from working properly, which is a major safety hazard as it cannot clear fog or frost from the windshield. A search of online forums and owner communities shows this is a widespread complaint from many other Hyundai owners, often identified as a failed blend door or blend door actuator, which requires the same expensive dashboard removal to repair.

After initial startup and drive for a short time, I come to a stop. Then after vehicle doesn’t want to accelerate as it normally would. Vehicle struggles to gain speed but, the engine revs excessively. I pull off the road and come to a stop and try to accelerate again and the same thing happens. I shut the vehicle off and wait a few minutes,then restart and the vehicle accelerates normally again. There were no check engine lights the when this has happened.

Air flow check engine light alerted and source was faulty fuel injector which required replacement of 4 fuel injectors.

The contact owns a 2021 Hyundai Sonata. The contact stated while pulling out of a parking lot, the vehicle failed to accelerate as intended and started shaking abnormally. The check engine warning light was illuminated. The vehicle was taken to the residence. The vehicle was towed to an independent mechanic where it was diagnosed that the fuel injector needed to be replaced. The vehicle was towed to a dealer where it was diagnosed that all four fuel injectors needed to be replaced. The vehicle was repaired. The manufacturer was not notified of the failure. The failure mileage was 47,000.

Overheated engine alarm came on while I was on the freeway on a rainy day. Vehicle was towed to Hyundai dealership in which service technician found that the part preventing water from leaking into the muffler was broken. Hyundai dealership has ordered replacement part but it is on backorder. The broken part that needed replacement has been on backorder for close to a month and there is not an eta of when the part will be received. Prior to the overheated engine alarm going off, cold air was blowing out of the vents even when the heat option was selected.

On 5 separate occasions the car has shut itself off while driving. After the first 2 times the car was taken to the dealership where they found nothing wrong and told us to replace the battery. The battery was replaced by the dealer and within the next two weeks the car shut itself off while driving 3 more times. The car will always start back up again right away. This is a very dangerous situation.

Coolant system leaks in to the engine or exhaust system, which is evident in white smoke exhaust and coolant level dropping. In my situation, I required an entire container of coolant to perform a daily commute, and the reservoir was empty by the time I made it to the dealership. Car is rendered undrivable due lack of coolant and engine overheating. My car was in the dealership repair facility for 6 weeks awaiting parts on back order due to nationwide shortage. A technical service bulletin has been issued for this manufacturer defect (23-em-009h). Cost of repairs was roughly $2,300.

My 2021 Hyundai Sonata hybrid seems to be leaking coolant into the exhaust system. Various reports online indicate that this is a consistent issue with 2020-2022 Hyundai Sonata hybrid models. A lot of the reports indicate that owners have tried getting theirs cars repaired for the same issue I have a various dealerships all across the us, but either haven't had any luck or have had a temporary fix for the issue, which proceeded to occur again every couple of months. I personally have had my car inspected by my personal dealership and they have confirmed the issue and have mentioned that other owners have brought theirs in to be checked out, but haven't really had luck. I believe that Hyundai should take responsibility for this and issue a recall on the affected models. I bought the car in good faith hoping for reliability but haven't had it for even 6 months now and this problem is here. For safety or myself and others on the road, this models of the Sonatas need to be recalled and repaired immediately. For reference, here is a reference for the complaints people have made online regarding the vehicle: 1. [xxx] 2. [xxx] . (the responses here are very detailed) [xxx] information redacted pursuant to the freedom of information act (foia), 5 u. S. C. 552(b)(6).

Ehrs coolant leak- problem started in [xxx] when engine overheated. The weather in michigan in inclement and being stranded in the intense cold can lead to loss of life. I had it towed to a Hyundai dealership that was unable to find the problem and in attempting to "find a leak" used the incorrect dye, necessitation transferal to another more competent dealership where the problem was diagnosed and was fixed with a replacement part. In December 2023 a TSB 23-em-009h was issued by Hyundai describing this problem and issuing a part (center muffler). I was not informed and the problem recurred. Currently this is the third episode and Hyundai after paying 95% of the previous cost, now only agrees to pay 85% and denies reimbursing me for the car rental. Warning lights appeared with all 3 occurrences. Hyundai should have issued a recall to obviate this. Information redacted pursuant to the freedom of information act (foia), 5 u. S. C. 552(b)(6).

This car has two problems. 2 weeks I was driving on the highway. All the sudden the shutoff and lost all power on the car. Thank god I pulled to the side of the road safely. Turned the car off and turned it back on. The car started to run normal. I took it to mechanic. They scanned the car with their computer. Said the car has no problems. Tested the battery and all other components. No problems found. This happened again yesterday on the highway driving. Car engine shuts off again. The car has engine problems as well. But Hyundai denies to address it.

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.

I have been to the dealership on three separate occasions due to the engine misfiring. Two ignition coils have been replaced so far and I recently returned to the dealership for the same issue. This time however, not only did the engine light come on but I went from a full tank to less than a quarter of a tank and the engine is making backfiring sounds. At that time the dealership said that they could not recreate the issue, I got my oil changed and went home. That was a week ago, I am back at the dealership today for the same thing; fuel dumping and backfiring sounds. While at the dealership today it turns out those backfiring noises were the fuel tank expanding so much so that it kept popping the seat up. They deemed the car unsafe to drive and it is currently at the dealership.

Driving 70 mph, warning lights and alarms "hybrid system failure" "vehicle shutting down" and then it does. No lights, no hazards, no power. Push button battery restart starts it again with no visible issues. Driving 30 mph, warning lights and alarms "hybrid system failure" "vehicle shutting down" and then it does. No lights, no hazards, no power. Push button battery restart starts it again with no visible issues. Driving 58 mph warning lights and alarms "hybrid system failure" "vehicle shutting down" and then it does. No lights, no hazards, no power. Push button battery restart starts it again with no visible issues. ^this is an ongoing issue. It's also been powerless several times while parked.

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.

The contact owns a 2021 Hyundai Sonata. The contact stated while driving 15 mph, the contact noticed that the passenger’s side rear seat level had become elevated. The contact stated that his daughter that was seated in the child seat head had started touching the top of the sunroof. The contact became aware of a gasoline odor coming from the engine. The contact also became aware that the vehicle was consuming an abnormal amount of gasoline. There was no warning light illuminated. The vehicle was taken to the dealer however, the diagnostic test result was undisclosed. The dealer unsure of how to service the vehicle. The vehicle was not repaired. The manufacturer was notified of the failure. The failure mileage was approximately 87,000. The VIN was not included.

I purchased this vehicle brand new. It is still under factory warranty. It has approximately 14k miles on it. I have followed all recommended maintenance procedures. During a routine maintenance appointment at the dealership (vancouver Hyundai 6802 ne 40th street, vancouver wa 98661) they identified a catastrophic engine failure due to internal component deterioration and the engine needs to be replaced. They have had my vehicle in their possession since [xxx] of this year for a total of 134 days. I have a case number at Hyundai # [xxx]. They have not been helpful in providing any information and as of now, I do not know when they even expect to receive a new engine. Information redacted pursuant to the freedom of information act (foia), 5 u. S. C. 552(b)(6).

Faulty engine thermostat.

Antifreeze is coming out of the exhaust. Heater is only blowing cold air. Repair shop said it is a common problem with the Hyundai hybrids. Was told I had to take it back to the dealership. The y repair shop said this is very common and is wondering why a recall has not been issued by the nthsb. Dealership has been unresponsive.

Hyundai 2021 Sonata hybrid. Blown head gasket. Reported 1,000 miles after warranty expired. Car was in the shop for hybrid battery issues. Repair completed. 2 weeks later smoke coming from the exhaust. Hyundai says blown head gasket - will not honor warranty as I was just a few thousand miles over warranty. Seems to be a common problem with the Hyundai not honoring the warranty.

My vehicle's heat stopped working suddenly. A short while later, I received and overheat warning for the engine. I had to stop repeatedly on the shoulder of the highway to allow the car to cool so I could move it to a safe space at the next exit. The dealer has confirmed that the coolant was leaking into the exhaust system and burning up. This resulted in white smoke, inconsistent power, and a stumbling engine when it would switch over from the electric to the gas engine. This problem comes on suddenly and can leave you in a very bad situation since there is no warning to this problem. The dealer reported my car had no coolant left in it which is why it was frequently overheating. I have read about this problem on many online forums and it seems to be very common in this car. Hyundai needs to create a fix.

I was on the highway going 60 mph then all of a sudden my vehicles rpm's jumped way up to 8 and completely lost power was on I-45 in conroe thankfully I was in the slow lane. I have attached pictures of my dash so I could get proof this time. I had to wait 7 minutes for the car to do anything. It also burned all of my engine oil. So had to buy oil for my vehicle. I just had my oil change 3 weeks ago. This has happened before on on the frontage road a few months ago. I have claims open with Hyundai customer care. I have been stating that my engine makes a clicking noise, it hesitates, and seizes all the time. I have had this problem since March of 2021 and I bought the car in January 2021. I know I am not a part of the engine recall but I should be. I am scared to drive it. Hyundai doesn't care one bit. Well enough is enough I will be getting rid of this death trap. If you are looking at Hyundai's don't waste your time or money.

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.

I have a 2021 Hyundai Sonata sel with a smartstream 2. 5l engine w/ gdi & mpi. I have have always heard a loud knocking noise coming from my engine since I got the vehicle when in park. When you are accelerating it hesitates and you can hear a knocking noise. I have taken it to the dealership multiple times and they were able to feel and hear what I was talking about but ensured me it was fine. Recently it has been a lot worse. On 10/18/2023 I was getting on to the highway from the feeder. I tried to accelerate to about 50 mph and I heard the same knocking noise and my rpms jumped all the way to the top. Then my car suddenly stopped getting on to the highway. It took it about a minute before I could start driving again. Luckily there was no one behind me because it could've been really bad. I got home and looked under the hood and it looked like oil had sprayed out of the engine. You could to see oil splatter on the fender. No one was hurt thankfully. I have been complaining about the knocking and hesitation while accelerating for almost 2yrs.

Discovered that I had no engine heat to use in the cabin with cooler outside temps. Checked coolant tank. Was nearly bone dry. 2021 hybrid is under warranty with only 35k miles on it and regular scheduled maintenance. Have also noticed puffs of white smoke upon easy acceleration and switching from battery to gas. Refilled engine coolant, but it continues to leak internally with use (no evidence of pooling under car) with short mile trips. Had to leave at dealership for repairs and cannot get a repair date for another month out. Other hybrid owners of 2020 and 2021 report their dealerships discovered the coolant is leaking into the engine and mixing with the exhaust (thus the white smoke). I am adding my car to the list of others who have reported the same problem.

The contact owns a 2021 Hyundai Sonata. The contact stated while driving 45 mph, the vehicle inadvertently lost motive power in the middle of the roadway and failed to restart. The vehicle was pushed to the shoulder of the roadway, where the failure persisted. No warning lights were illuminated. The vehicle was towed to the dealer, who determined that there was no oil in the engine, causing the engine to seize. The vehicle was then towed to another dealer, who confirmed the diagnostic results. The contact stated that an oil change was performed three days prior to the failure. The vehicle was not repaired. The manufacturer was notified of the failure, and a case was opened. The failure mileage was 44,000.

This car is a hybrid the car has a 12v battery reset system which stops the 12v battery from draining to zero voltage. This is a design feature. However, since purchasing this car we have had hybrid engine failure warnings happen 3 times, in 2 months. When this happens the car engine shuts down, no matter at what speed you are driving! the car gives a warning on the dashboard that states - hybrid system failure - and the engine shuts down. The dashboard goes completely bland as all electronics are switched off. This has happened 3 times, 2 of them occurred on the freeway at high speed. Luckily we were able to pull over without being impacted by another vehicle. After a few seconds of stopping we are able to push the 12v battery reset switch and the engine restarts when the start button is depressed. After the first incident the car was given to the local Hyundai dealer and they found nothing wrong with the car. It has happened twice since the car was returned to us and the car is currently in the Hyundai dealership, a different one, for diagnosis. We do not want to drive this car until the fault is determined and corrected.

The contact owns a 2021 Hyundai Sonata. The contact stated while driving at an undisclosed speed, the vehicle lost motive power. Additionally, the forward collision avoidance failed to function as intended. The contact stated that the sensor was braking prematurely. The vehicle was taken to the dealer; however, the failure was not duplicated. The contact stated while driving out of the driveway, the vehicle lost motive power. The vehicle failed to restart. The dealer was contacted and made aware of the failure. The vehicle was not diagnosed or repaired by an independent mechanic or the dealer. The manufacturer was not made aware of the failure. The failure mileage was unknown.

The coolant reservoir has been dropping showing levels below min even after topping it off.