Some vehicles may exhibit difficulty starting in cold weather. This bulletin provides the procedure to perform an inspection on the starter magnetic switch for potential freezing and, if necessary, replace the starter magnetic switch (solenoid) assembly.
full bulletin at NHTSA ↗2021 Hyundai Sonata engine problems
severe Owners of the 2021 Hyundai Sonata have filed 19 NHTSA complaints about the engine at roughly $3,100 to repair (U.S. federal records, as of July 2026). Source: NHTSA Office of Defects Investigation. See engine across all vehicles →
Complaints
19
Recalls
0
Avg fix
$3,100
| Model year | engine complaints |
|---|---|
| 2017 Sonata | 292 |
| 2018 Sonata | 138 |
| 2019 Sonata | 68 |
| 2020 Sonata | 11 |
| 2021 Sonata (this page) | 19 |
| 2022 Sonata | 10 |
| 2023 Sonata | 13 |
1crash
When does it fail?
Of the 19 engine complaints filed for the 2021 Hyundai Sonata, here's the actual mileage breakdown — failures cluster heaviest at 0-25,000 mi.
0-25k
25-50k
50-75k
75-100k
100-125k
125-150k
150k+
Each bar shows the share of total complaints filed at that mileage range. Peak failure window highlighted. Some owners report problems earlier; some make it well past 150,000 miles symptom-free. Maintenance habits and driving conditions shift the curve as much as mileage alone.
Is there a fix? Manufacturer service bulletins
The manufacturer has issued service bulletins covering engine on this vehicle — documented repair instructions, service campaigns, or warranty extensions sent to dealers. A TSB isn't a recall (it's not a free safety remedy), but it's the manufacturer acknowledging the issue and how to fix it.
Some Sonata (DN8, DN8A) vehicles may have DTCs P218100, P2181F0, and/or P2181F1 (Cooling System Performance) set in the Engine Control Module, resulting in an illuminated Check Engine warning lamp. Follow the procedure in this TSB to replace the Integrated Thermal Management (ITM) module and update both the Engine Control Module (ECM) and Transmission Control Module (TCM) if applicable. Follow the flowchart in this TSB to update the appropriate modules.
full bulletin at NHTSA ↗Certain Sonata (DN8) and Sonata (DN8A) vehicles may experience issues with the air conditioning due to damaged wiring in the engine room junction box. This bulletin provides instructions to replace the multi-fuse, reroute the damaged wiring using the blower wiring kit, and replace the fuse label.
full bulletin at NHTSA ↗Certain 20-22MY Sonata (DN8a), 21-23MY Santa Fe (TMa), and 22-23MY Tucson (NX4a) vehicles may experience a warning lamp illumination for a diagnostic trouble code P2181 that is related to the Integrated Thermal Management Module (ITM). Follow the service procedure outlined in this bulletin to replace the ITM.
full bulletin at NHTSA ↗This bulletin provides the procedure to update the Engine Control Module (ECM) and/or the Transmission Control Module (TCM) for 2020-2023MY Sonata (DN8/DN8a) vehicles to improve operation of the Idle Stop and Go (ISG) system. Under certain circumstances the vehicle may not restart after the ISG system has engaged and requires a manual restart due to the lack of intake manifold pressure recovery.
full bulletin at NHTSA ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
The failure pattern owners describe
Owners report multiple distinct engine failure modes affecting the 2021 Sonata. The most common complaint involves the Exhaust Heat Recovery System (EHRS)—specifically part #28600-L5210—where the internal heat exchanger fails and allows coolant to leak directly into the exhaust. This creates thick white smoke that blocks visibility, causes rapid coolant loss and engine overheating, and forces power loss during driving. Some owners experience recurring EHRS failures even after TSB 23-EM-009H repair. Hyundai issued a technical service bulletin acknowledging the defect in 2020-2023 Sonata Hybrids but has not issued a safety recall.
Owners also report sudden loss of power during highway acceleration and passing, with engines stalling and requiring complete shutdown to restart. Some vehicles drop into limp mode, restricting speed to 15-30 mph. One owner describes a 2.5L turbo with thermostat housing failure causing turbo boost to drop to zero and oil temperatures running 30-40 degrees above normal despite four service visits where dealers claim the symptoms are normal.
Additional failures include complete oil loss and engine seizure three days after an oil change, a persistent engine knock that worsens over two years before culminating in catastrophic mechanical failure with oil splatter, and a cylinder 3 misfire with EVAP errors causing severe shaking. One owner's engine at 14,000 miles required complete replacement while still under factory warranty. Dealers frequently cannot replicate issues, return vehicles undiagnosed, or claim problems are normal operation.
Same Hyundai Sonata engine reports on nearby years: 2018 · 2019 · 2023
Failure modes owners describe
Exhaust Heat Recovery System (EHRS) coolant leak
The internal core of the EHRS (part #28600-L5210) fails, allowing coolant to leak into the exhaust stream. This creates dense white smoke that obscures visibility and causes rapid coolant loss, engine overheating, and loss of power.
When: Between 35,000 and 90,000+ miles; some failures recur after TSB repair at 35k, recurring at 71k
Symptoms owners cite: Dense white glycol smoke from exhaust, completely obscuring driver visibility; Sweet burning smell; Engine overheating warning on dashboard; Rapid coolant loss and consumption; Loss of power and near-stall in traffic; High engine oil temperatures (30-40 degrees above normal)
Codes mentioned: Engine Overheating warning
Repairs/costs cited: Failed component replaced by dealer (TSB 23-EM-009H repair confirmed at multiple dealerships). One invoice #174281 from Washington Hyundai noted second failure of same component. Owner reported dealer cost estimate of ~$3,000 for full system replacement out of warranty; coolant-poisoned O2 sensors were not replaced by manufacturer.
Recalls/TSBs owners mention: Hyundai Technical Service Bulletin 23-EM-009H issued for 2020-2023 Sonata Hybrids; no safety recall issued despite acknowledged defect. Parts availability inconsistent—some dealers report parts in stock, others report unavailability.
Loss of power and engine stalling under acceleration
Engine suddenly loses power, limits RPM, and stalls during highway acceleration or passing, requiring complete vehicle shutdown and restart to clear the limp mode. Multiple occurrences across different driving scenarios.
When: Throughout ownership, multiple incidents reported; one at 35k miles, others undisclosed
Symptoms owners cite: Sudden loss of acceleration power on highway on-ramps and passing maneuvers; RPMs jump to maximum (8000+) then engine loses all power; Vehicle enters limp mode, limiting speed to 15-30 mph; Engine light may flash or stay on; Requires full engine shutdown to reset; Occurs repeatedly even after dealer visits
Codes mentioned: Check Engine Light (flashing or steady), Misfire codes (Cylinder 3 misfire noted in at least one case)
Repairs/costs cited: Dealerships have replaced fuel injectors, catalytic converter, and performed diagnostics without fully resolving the issue. One owner reported three invoices pending repairs. Dealers occasionally report 'mis-fire cleared on its own' or 'no code found' despite recurring stalling.
Recalls/TSBs owners mention: Multiple owner complaints state they are not part of existing engine recalls despite similar symptoms to recalled vehicles. Hyundai has open cases with some owners but no definitive root cause or remedy provided.
Intake Thermostat Housing Unit (ITMS) failure causing loss of boost and overheating
Thermostat housing unit in the turbo 2.5L engine fails, causing turbo boost to drop to zero and engine overheating warnings. Chronic oil temperature elevation and fan running constantly despite repairs.
When: Multiple incidents throughout ownership; one during highway entry
Symptoms owners cite: Sudden loss of acceleration and turbo boost dropping to 0 psi; Engine overheating warning on dashboard; Oil temperatures running 30-40 degrees higher than normal; Fans running at full blast continuously, even after engine shut off; Loss of boost during passing, nearly causing accidents; Issue recurring despite four service center visits
Codes mentioned: Engine Overheating warning
Repairs/costs cited: Service center unable to 'replicate the issue' on four separate visits. Dealers claim fan and oil temperature issues are 'normal' despite owner's assertion they are not.
Recalls/TSBs owners mention: Owner reports this is a 'well-known' issue across DN8 platform (2.5L turbo DCT engine) affecting 'hundreds if not thousands' of people, citing Car and Driver article coverage, but no official recall or TSB mentioned.
Engine knock, hesitation, and catastrophic mechanical failure
Persistent loud knocking noise from engine during idling and acceleration, accompanied by hesitation. Knocking worsens over time and culminates in sudden RPM spike, complete loss of power on highway acceleration, and oil splatter from engine bay.
When: Since new (2021 model); critical failure at ~44,000 miles on highway
Symptoms owners cite: Loud knocking noise from engine when in park and during acceleration; Hesitation during acceleration; Knocking noise worsens significantly over ~2 years of ownership; Sudden RPM spike to maximum during highway acceleration; Complete loss of power on highway on-ramp; Oil splatter visible on fender and under hood after critical event; Engine appears seized or requires extended restart time
Codes mentioned: Check Engine Light (not always illuminated before failure)
Repairs/costs cited: Dealership felt and heard the knocking multiple times but assured owner it was normal and acceptable. No repairs performed despite repeated complaints over nearly 2 years.
Recalls/TSBs owners mention: None documented; dealership dismissed concerns without diagnosis or repair.
Complete loss of oil, engine seizure, and power loss
Engine loses all oil between scheduled services, causing oil starvation, seizure, and complete loss of motive power. Vehicle cannot restart and requires towing.
When: At 44,000 miles; three days after scheduled oil change
Symptoms owners cite: Complete loss of motive power while driving at 45 mph on roadway; Engine fails to restart; No warning lights illuminated before failure; Dealer diagnosis: no oil in engine; Oil change performed three days before failure
Repairs/costs cited: Confirmed by two separate dealers. Vehicle not repaired; case opened with manufacturer.
Recalls/TSBs owners mention: Case opened with Hyundai; no details on root cause or resolution provided.
Cylinder misfire, fuel system, and EVAP errors
Engine develops cylinder 3 misfire along with EVAP system and fuel injector faults, causing severe shaking, vibration, and check engine light at low speeds.
When: At approximately 3:00 AM during routine driving
Symptoms owners cite: Vehicle suddenly shaking and vibrating while driving; Check Engine Light illuminated; Engine shaking severely while stopped at traffic light; Vehicle can only drive very slowly after incident; No warning before failure occurred
Codes mentioned: Cylinder 3 misfire, EVAP system errors, Faulty fuel injector code
Repairs/costs cited: Diagnostic performed at local repair shop confirmed three separate faults.
Recalls/TSBs owners mention: None documented.
Sudden oil pressure loss and limp mode activation during acceleration
During sudden acceleration or passing, engine experiences abrupt loss of oil pressure and enters fail-safe limp mode, severely restricting power. Oil pressure warning light illuminates. Issue recurs repeatedly and requires full engine shutdown to reset.
When: Recurring issue at approximately 50,000 miles
Symptoms owners cite: Sudden loss of power and oil pressure during acceleration or highway on-ramps; Fail-safe mode limits acceleration; Sudden decrease in speed and velocity; Oil pressure warning light illuminates; Requires complete vehicle shutdown to reset; Problem returns with next sudden acceleration; Clicking noise reported in engine
Codes mentioned: Oil Pressure warning light
Repairs/costs cited: Owner states engine burns all oil, requiring top-ups; oil was changed 3 weeks before one failure. Multiple open claims with Hyundai Customer Care.
Recalls/TSBs owners mention: Owner states Hyundai has similar recall on comparable models but VIN not listed in current recall.
Transmission fluid leak from engine area
Transmission fluid leaks from the engine area while vehicle is parked for routine maintenance. Mechanic identifies the fluid as flammable transmission fluid.
When: At 5,600 miles, discovered during oil change service
Symptoms owners cite: Transmission fluid visible leaking from engine area
Repairs/costs cited: Independent mechanic diagnosed; dealership informed but reported inability to diagnose for approximately three weeks due to backlog.
Recalls/TSBs owners mention: Case opened with manufacturer; no further details on diagnosis or remedy provided.
Sudden engine shutdown in traffic with no warning lights
Engine loses all power and fails to restart while driving at low speed on roadway. No warning lights illuminate before or during failure. Vehicle becomes immobilized in traffic.
When: At 32,000 miles, middle of road during normal driving
Symptoms owners cite: Sudden complete loss of engine power; Engine fails to restart; No warning lights illuminated before or during event; Vehicle becomes immobilized in traffic
Repairs/costs cited: Vehicle towed; independent repair shop diagnoses transmission failure (note: complaint narrative states 'repair shop reports the transmission is no good,' but failure mechanism unclear).
Recalls/TSBs owners mention: Hyundai refused to cover rental vehicle; dealership unable to schedule service for 1-2 weeks.
Gasoline consumption and internal coolant routing malfunction
Vehicle consumes abnormal amounts of gasoline and develops a gasoline odor. Rear seat level becomes elevated during driving. Diagnostic test result undisclosed by dealer.
When: At 87,000 miles
Symptoms owners cite: Abnormal gasoline consumption; Gasoline odor from engine area; Passenger side rear seat becomes elevated during driving; No warning lights illuminated
Repairs/costs cited: Vehicle taken to dealer; diagnostic results undisclosed. Dealer unsure how to service vehicle; not repaired.
Recalls/TSBs owners mention: Manufacturer notified; no details on response provided.
Catastrophic internal engine deterioration requiring full engine replacement
Engine develops internal component deterioration requiring complete engine replacement. Vehicle still under factory warranty with only 14,000 miles. Dealer has vehicle for extended period; no new engine received despite being held for 134 days.
When: Identified at 14,000 miles during routine maintenance
Symptoms owners cite: Catastrophic engine failure identified during routine maintenance
Repairs/costs cited: Full engine replacement required. Dealer held vehicle for 134 days without receiving replacement engine or providing timeline for delivery.
Recalls/TSBs owners mention: Case opened with Hyundai; dealership and manufacturer have not provided helpful information or timeline for engine availability.
Synthesized from 19 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 3 most recent
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…
The contact owns a 2021 Hyundai Sonata. The contact stated that while the vehicle was at an independent mechanic for an oil change, the mechanic diagnosed the vehicle with transmission fluid leaking from the engine. The mechanic informed the contact that the transmission fluid leakage was flammable. The dealer was made aware of the failure but informed the contact that they were backed up with…
Oct 12: Engine stalled exiting I95 in Kittery Maine. Engine light flashed but did not stay on. Was able to get to safe place but car would not go more than 15mph. Hampton Huyndai reported mis-fire but stated it cleared on its own. Oct 17th: Engine stalled on highway ramp to I495, nearly causing me to be rear ended by other vehicles. Car would not go more than 15 mph. Engine light stayed on.…
Had engine trouble with your 2021 Hyundai Sonata?
File a complaint with NHTSA → It's free, official, and how every report above got here — owner filings are the federal safety record this page is built on.
Common questions
How serious is the engine problem on the 2021 Hyundai Sonata?
It's a meaningful issue. 19 complaints have been filed and the failure mode causes operational problems for owners. Repairs average $3,100.
At what mileage does the engine typically fail?
Based on the 19 complaints filed, engine issues most often appear around 45,533 miles. Some report problems earlier; some make it well past 150,000 with no symptoms. Maintenance habits matter — vehicles that received timely fluid services and were not regularly overworked tend to last longer.
What does it cost to fix?
Independent shops typically charge around $3,100 for engine repairs on this vehicle. Dealer pricing tends to run 20-40% higher. The exact figure depends on the specific failure mode, parts availability, and your local labor rates. If you're outside factory warranty, an extended service contract often covers this category.
Are there any recalls related to engine?
No active recalls currently cover engine issues on this vehicle. The complaints filed represent owner-reported failures that haven't risen to the level of a manufacturer-issued recall — but they're still worth knowing about before you buy or budget for repairs.
Related
Complaint and recall data sourced from the National Highway Traffic Safety Administration (NHTSA)
public records database. Verify the raw federal record at
nhtsa.gov/vehicle/2021/Hyundai/Sonata.
Severity ratings are derived from reported crashes, fires, injuries, and fatalities. Repair cost estimates are
independent-shop national averages and may differ in your area. Some links on this page are affiliate links.