2021 Hyundai Sonata Hybrid Engine 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.

NHTSA ID

11755133

Incident

Aug 5, 2026

See attached document for complaint.

NHTSA ID

11730136

Incident

Jan 26, 2026

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

NHTSA ID

11656895

Incident

Apr 15, 2025

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.

NHTSA ID

11647194

Incident

Feb 12, 2025

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.

NHTSA ID

11646538

Incident

Jan 22, 2025

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)

NHTSA ID

11636925

Incident

Jan 19, 2025

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)

NHTSA ID

11635700

Incident

Jan 13, 2025

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.

NHTSA ID

11612394

Incident

Aug 27, 2024

Coolant leak acting like blown head gasket. Coolant was leaking into the exhaust system. Defective EHRS system

NHTSA ID

11609725

Incident

Feb 20, 2023

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.

NHTSA ID

11595049

Incident

Jun 16, 2024

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.

NHTSA ID

11592346

Incident

Jun 3, 2024

Initially had loss of cabin heat. Later, vehicle randomly overheated. Repair shop replaced EGR due to finding confidant buildup of water/coolant mix. Within one week, problem returned. Dealer notified me that while replacing another part they found a TSB for coolant leakage into exhaust that was consistent with my issue. After research, it is clear that this is a widespread failure and should be a recall.

NHTSA ID

11571605

Incident

Jan 9, 2024

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.

NHTSA ID

11565750

Incident

Dec 20, 2023

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.

NHTSA ID

11562721

Incident

Dec 26, 2023

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.

NHTSA ID

11560898

Incident

Dec 18, 2023

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.

NHTSA ID

11558373

Incident

Nov 25, 2023

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

NHTSA ID

11556589

Incident

Jun 15, 2023

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.

NHTSA ID

11548049

Incident

Sep 26, 2023

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

NHTSA ID

11536792

Incident

Jul 31, 2023

The contact owns a 2021 Hyundai Sonata. The contact stated that while driving at an undisclosed speed, he received an alert indicating that the engine was overheating and to pull over. No warning lights were illuminated. The contact then veered to the side of the road and waited approximately 15 minutes before restarting the vehicle. The vehicle was then taken to the dealer where the vehicle remained. The vehicle was diagnosed, and it was determined that the engine coolant bypass valve needed to be replaced. The vehicle had not yet been repaired. The manufacturer was not notified of the failure. The failure mileage was approximately 32,547.

NHTSA ID

11521686

Incident

Apr 12, 2023

Mileage

32,547 mi

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.

NHTSA ID

11518107

Incident

Apr 10, 2023

The cabin heater started blowing cold air in February. One shop said the car was low on coolant and topped it off. I made an appointment to take the car to a dealer because it's still under warranty (<37k miles). I had to wait 3 weeks. A few days before my appointment, the cabin heater started blowing cold air, again. There is no indicator that the coolant is low. The engine temperature is one of a dozen gauges one can scroll thru, but the "engine overheating" warning started flashing before I thought to check the temperature guage. Smoke came out of the exhaust and, once stopped, from under the hood. There was a risk of an engine fire and/or permanent damage to the engine.

NHTSA ID

11515318

Incident

Mar 14, 2023

Engine oil plug backed out while driving causing loss of all engine oil in the mountains. Drive time was one hour when oil lamp turned on as we reached our destination. Oil check stick had no oil on it and the whole undercarriage and rear of the car was covered in engine oil. Made an attempt to refill oil and plug fell all the way out and poured the new oil onto the ground. The oil plug is not visible or accessible due to a plastic cover on the underside of the car. The vehicle was towed to Elk Grove Hyundai dealership for service since they were the last hands on the car for regular maintenance. It was confirmed by the dealership the oil plug backed out on it's own. My family's safety was compromised as we were driving at night in steep mountains during high traffic time. There would be nowhere to go if the engine ceased and would cause an accident on HWY 50 in California. Also a full six quarts of oil was leaking on the back roads, highway, and residential roads, and eventually in a high school parking lot was were the bulk of the oil was spilled. The is an environmental hazard at public school Eldorado High School.

NHTSA ID

11509128

Incident

Jan 26, 2023

Very loud car alarms sounded, e.g., it sounded like a something like a red alert in an old Star Trek episode. warning light indicated engine overheated, extreme exhaust/smoke bellowed out from rear of car while decelerating on highway exit ramp. My wife and I were inside the car during this event. This event happened on 5 pm EST December 9 at Hamilton Avenue exit on Ohio 126 Cross County Highway (Ronald Reagan Highway) in the Cincinnati metropolitan area. Had to park car within one mile. I had the car towed to the nearest dealer after it had cooled for 1 +hour. I was afraid the engine was going to explode or catch fire as I was decelerating. The dealer suggests the heat exchanger needed replacement. However, after 45 days, Hyundai has not shipped the heat exchanger that I have been made aware. I am concerned this event may be likely to reoccur and with resulting potential injuries to the occupants inside.

NHTSA ID

11503289

Incident

Dec 9, 2022