2021 Hyundai Sonata engine problems

ENGINE

Going down the road driving the car lost power and went in limp mode with no warnings on the dash at all!

NHTSA complaint #11754136 — an unverified report by a vehicle owner.

ENGINE

At approximately 130,000 miles, vehicle developed and internal coolant leak caused by a failed Exhaust Heat Recovery System (EHRS) in the center muffler assembly, matching TSB 23-EM-009H - a known manufacturing defect documented by Hyundai. Coolant has been slowly leaking internally into the exhaust system. The authorized Hyundai dealership initially failed to diagnose the internal leak and told me there was no leak and wanted to send me home. After pushing back, the internal leak was confirmed. If not caught, this defect could result in engine overheating or complete engine failure without warning. Hyundai Motor America has denied goodwill coverage despite this being a documented manufacturing defect.

NHTSA complaint #11746137 — an unverified report by a vehicle owner.

ENGINE

The car will idle high around 1200 rpms. The car will most of the times fix the issue when you turn the car off and back on but it will start again after driving. This is a known issue with the car. I have had the egr valve replaced since it will pop up the codes P240F and P049 for egr slow response and control position exceeded learning limit but the problem came back within two days. I did find a forum that deals with the joint connector repair but this needs to be a recall as I have come across many people who have this problem and paying out of pocket to fix it.

NHTSA complaint #11741201 — an unverified report by a vehicle owner.

ENGINE

The contact owns a 2021 Hyundai Sonata. The contact stated while driving at an undisclosed speed, the engine shuddered and the engine stalled. In addition, the engine seized. No warning lights were illuminated. The contact stated that the vehicle was seized in the middle of the road. The contact stated that while attempting to start the vehicle, the vehicle started. The failure reoccurred. The vehicle was towed to the residence. The vehicle was not diagnosed or repaired by an independent mechanic or dealer. The manufacturer was made aware of the failure. The failure mileage was approximately 140,000.

NHTSA complaint #11738864 — an unverified report by a vehicle owner.

ENGINE

The Exhaust Heat Recovery System (EHRS) has failed for the second time on this vehicle. The first failure occurred at approximately 35,000 miles and was repaired under Hyundai Technical Service Bulletin 23-EM-009H, which Hyundai issued to address this exact defect across 2020-2023 Sonata Hybrid models. The vehicle has now reached 71,000 miles and is experiencing the identical symptoms: coolant loss, overheating, and white exhaust smoke. The EHRS shares a coolant loop with the hybrid battery thermal management system. Coolant loss from this failure puts the hybrid battery and power electronics at risk of overheating, creating a potential fire and safety hazard. The recurring nature of this failure following an official TSB repair suggests the root cause has not been adequately addressed by Hyundai's current repair protocol.

NHTSA complaint #11730992 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11727380 — an unverified report by a vehicle owner.

ENGINE

Hyundai technical service bulletin 23-EM-009H (EHRS COOLANT LEAK) - AKA a faulty heat exchange that causes the coolant to leak into the exhaust and burn away. Resulting in a very hard to diagnose coolant disappearance. This should be a recall. They have literally already acknowledged a manufacturer defect with the service bulletin. The problem is that in most cases, it occurs out of the 60k or 100k warranty. The dealer seems to have discretion as to which of the mileage limits apply. One dealer in NC told me 60k and my local in SC told me 100k. My problem started at ~90k, but was just topped off on fluid and repaired as "normal evaporation". Now 12k later at 102k, they acknowledged the TSB but claimed I was out of warranty. With me being out of warranty, they claimed that Hyundai would not send them tsb parts and that I would need to replace the whole system with the normal skus around $3k.

NHTSA complaint #11725107 — an unverified report by a vehicle owner.

ENGINE

P0471 code before 55k miles even after repair is made

NHTSA complaint #11721861 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11719681 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11719316 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11718194 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11709821 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11709919 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11698349 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11676441 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11645969 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11642341 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11628830 — an unverified report by a vehicle owner.

ENGINE

2021 Hyundai Sonata 59,850 miles RPM jumps to around 1,300 at zero miles on occasion. If I am stopped, at a red light or behind other stopped autos, the vehicle jumps forward when I take my foot off the brake. Because this happens quite often, I am aware of this and keep my foot on the brake until other vehicles are out of the way to avoid bumping into them. When this happens, I can cruise at 30 miles per hour without having my foot on the accelerator, I can slow down or stop by applying the brakes but the engine RPM stays at 1,300. If I stop and shut off the vehicle and restart, the operation goes back to normal but occurs again later. The Hyundai dealer has had the vehicle back 9 times but the issue continues. The first few times, they could not find an issue, I returned to the shop when this was happening and the service manager and a technician observed this condition, the EGR valve was replaced. Was OK for a bit but condition returned, the computer was then replaced. Condition continued. Brought the vehicle back and a scan was done and system “re-learned. After a short time the condition returned. Went back to the service center and they did another scan and another re-learn. Condition returned 4-5 days later. Problem still not resolved. Have 59,850 miles on the vehicle, warranty expires at 60,00 miles. This started around July 1, Now October 5. Waiting for a loaner so the service center can drive it around until the situation occurs and they can bring it in immediately for diagnosis. This is the same issue as reported for the same year vehicle in July 2022.

NHTSA complaint #11618313 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11615411 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11603481 — an unverified report by a vehicle owner.

ENGINE AND ENGINE COOLING

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 who 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 was 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.

NHTSA complaint #11590388 — an unverified report by a vehicle owner.

ENGINE

faulty engine thermostat

NHTSA complaint #11579000 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11559246 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11551474 — an unverified report by a vehicle owner.

ENGINE

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.

NHTSA complaint #11546386 — an unverified report by a vehicle owner.

ENGINE

The issue is well known across the DN8 platform, hundreds if not thousands of people have this problem.Car and driver even did an article on a car with this same 2.5L turbo DCT engine having the same problem! The problem is the ITMS or thermostat housing unit. I first experienced this getting on to a highway, I lost all acceleration, the turbo dropped to 0 pSI and I received an engine overheating warning on the dash. After pulling over the car resumed normal driving, but with oil temps running 30-40 degrees higher than normal. Since then, I have had loss of boost and acceleration when passing around cars which has almost caused accidents, oil temps constantly running very high and fans constantly running on full blast even after car is off. I have been to the service center 4 times, and they have failed to "replicate" the issue and stated the fan and oil problem is "normal" which it is not. This problem needs to be addressed before somebody gets seriously hurt due to loss of power unexpectedly while driving. PLEASE help! Thank you for your time.

NHTSA complaint #11526848 — an unverified report by a vehicle owner.

ENGINE

When attempting to pass other vehicles or under quick acceleration such as an on ramp to the highway, the vehicle will experience a sudden loss of power and oil pressure resulting in a fail safe mode which limits your acceleration and causes a sudden decrease in speed and velocity. The issue results in the oil pressure light illuminating and requires the vehicle to be stopped and completely turned off to reset then once turned back on, the problem is “gone” until a sudden acceleration occurs again, which results in the same issue happening. There is a current recall out for similar models but my vin is not listed. I have approximately 50k miles on the car, and am the first owner.

NHTSA complaint #11525992 — an unverified report by a vehicle owner.

ENGINE

My 2021 Sonata has 32,000 miles & it broke down in the middle of the road. My safety & my daughters safety were at risk. We could have been hit or killed. There were no warning lights. It had to be towed. Repair shop reports the transmission is no good. This vehicle should not have transmission issues. Hyundai will not even cover a rental car. The dealership can’t even work on it for 1-2 weeks. I work & have kids. I need a vehicle. The car breaking down in the middle of the road with no warning is dangerous.

NHTSA complaint #11511312 — an unverified report by a vehicle owner.