Certain Santa Fe (TMA), Santa Fe Sport (AN), Sonata (LFA), and Tucson (TL) vehicles equipped with Theta II engines may exhibit elevated engine-out emissions. This bulletin provides instructions for updating the Engine Control Module (ECM) to address this condition.
full bulletin at NHTSA ↗2015 Hyundai Sonata engine problems
severe Owners of the 2015 Hyundai Sonata have filed 412 NHTSA complaints about the engine, typically surfacing around 75,000 miles 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 →
Failure mileage
Complaints
412
Recalls
0
Avg fix
$3,100
| Model year | engine complaints |
|---|---|
| 2011 Sonata | 691 |
| 2012 Sonata | 382 |
| 2013 Sonata | 545 |
| 2014 Sonata | 215 |
| 2015 Sonata (this page) | 412 |
| 2016 Sonata | 342 |
| 2017 Sonata | 292 |
| 2018 Sonata | 138 |
| 2019 Sonata | 68 |
2crashes
22fires
When does it fail?
Of the 412 engine complaints filed for the 2015 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.
What stands out
Engine accounts for 37% of every owner complaint on file for this vehicle — the dominant problem area across 12 categories tracked.
Owners have filed 412 engine complaints with NHTSA against this vehicle, but no formal recall covers the issue — the federal record reflects what manufacturers have admitted, not everything owners are reporting.
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.
Certain Santa Fe (TMA), Santa Fe Sport (AN), Sonata (LFA), and Tucson (TL) vehicles equipped with Theta II engines may exhibit elevated engine-out emissions. The California Air Resources Board has determined that these vehicles may be releasing air pollutants which exceed Federal and California standards.
full bulletin at NHTSA ↗Following completion of Service Campaign 9C2 (Theta II Emissions Improvement), certain vehicles may exhibit a brief hesitation or rough shifting condition during cold start operation. If present, this condition is expected to occur only within approximately the first 1-3 minutes after engine start, while the catalyst is reaching its normal operating temperature.
full bulletin at NHTSA ↗Following completion of Service Campaign 9C2 (Theta II Emissions Improvement), certain vehicles may exhibit a brief hesitation or rough shifting condition during cold start operation. If present, this condition is expected to occur only within approximately the first 1-3 minutes after engine start, while the catalyst is reaching its normal operating temperature.
full bulletin at NHTSA ↗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 ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
The failure pattern owners describe
The 2015 Hyundai Sonata's engine—particularly the Theta II 2.0L and 2.4L variants—exhibits a cluster of catastrophic and progressive failures. The most severe is sudden engine seizure while driving, often without warning. Owners describe the engine locking up due to connecting rod bearing failure, sometimes with a loud knocking noise seconds before shutdown. Several report this happening as low as 12,000 miles; others at 60k–165k miles. A few narratives include engine fire.
Excessive oil consumption precedes many seizures. Owners add 1–2 quarts weekly or every 300–500 miles, starting around 30k–100k miles. Dealers perform repeated "oil consumption tests" (owners cite 11–15 visits) but often refuse to authorize engine replacement until catastrophic failure occurs. Interim fixes—gasket replacement, combustion chamber cleaning—fail to address the root cause.
Engine control module failures and limp-mode events (car drops to 20 mph) are common, sometimes recurring after software updates or ECM replacement. Some owners report multiple engine replacements under recall, only to have the replacement fail the same way or experience new failures like head gasket leaks.
Warranty denials are widespread. Hyundai cites salvage title, missing software updates, alleged maintenance neglect, or closed recall status to refuse coverage—contradicting owners' maintenance records and its own settlement warranty. Owners also report misleading dealer guidance: told to "keep putting oil in it until the engine blows," or directed to dealerships with expectation of reimbursement that never materializes. Repair costs, when not covered, range from $5,500 to $14,000+ with multi-month delays and parts on back order.
Same Hyundai Sonata engine reports on nearby years: 2012 · 2013 · 2014 · 2016 · 2017
Failure modes owners describe
Catastrophic engine seizure / connecting rod bearing failure
Engine suddenly seizes or stops dead while driving, often with no warning. Owners report the engine locking up internally due to connecting rod bearing failure, sometimes described as a rod going through the engine block. This is the most critical failure mode cited across narratives and is linked to the Theta II engine defect.
When: Variable—occurs between roughly 30k and 165k miles; some early failures around 12k–34k miles; typically without warning
Symptoms owners cite: Sudden loss of power while driving; Engine knocking or loud knocking noise before failure; Complete engine shutdown with inability to restart; Oil light on or oil level critically low; Smoke from engine or exhaust; No prior warning lights in many cases
Codes mentioned: P1326 (knock sensor code), Check engine light (sometimes absent until after failure)
Repairs/costs cited: Full engine replacement required; costs cited range from $5,500 to $14,000+ depending on dealer and whether warranty covers it. Owners report difficulty obtaining warranty coverage even under recall.
Recalls/TSBs owners mention: Hyundai recalls (Campaign 953/KSDS update); Theta II engine warranty extension; TXXI Class Action Settlement with 'Limited Lifetime Warranty' for connecting rod bearing failure. However, multiple owners report denials citing salvage title, lack of prior software update, or alleged maintenance neglect.
Excessive oil consumption
Engine burns or leaks oil at an abnormally high rate, forcing owners to add 1–2 quarts every few hundred miles or weekly. This precedes many catastrophic failures and is often unaddressed by dealers until engine seizure occurs.
When: Typically begins between 30k–100k miles and worsens over time; some owners report it as early as 64k miles
Symptoms owners cite: Oil level dropping rapidly between changes; Need to add oil every week or every 300–500 miles; Oil light illuminating intermittently; Low oil on dipstick with no visible external leaks; White smoke or fumes from exhaust or engine; Oil spattering from exhaust pipes onto tires; Burned oil smell inside cabin
Codes mentioned: Oil light (inconsistent warning)
Repairs/costs cited: Dealers often perform 'oil consumption tests' requiring multiple trips (owners cite 11–15+ visits). Repairs attempted include gasket/seal replacement, valve cover gasket replacement, combustion chamber cleaning (cost ~$400), or engine replacement. Many dealers refuse to address until engine fails.
Recalls/TSBs owners mention: No formal recall for oil consumption alone; class action lawsuit (TXXI) settled but some model years/trims excluded. Hyundai denies coverage citing maintenance neglect or refuses until catastrophic failure occurs.
Limp mode / power loss and drivability issues
Vehicle suddenly enters a protective 'limp mode' that limits power to 20 mph, or experiences hesitation, jerking, stalling, and inability to accelerate. Often triggered by check engine light and knock sensor codes.
When: Can occur early (12k–20k miles) or later; sometimes recurs repeatedly despite repairs
Symptoms owners cite: Sudden loss of power while driving (car drops to 20 mph max); Check engine light illumination (solid or flashing); Engine knocking or rough running; Hesitation and jerking when accelerating; Engine stalling, especially in traffic or on highway merges; Vehicle entering 'limp mode' despite software updates
Codes mentioned: P1326 (knock sensor code), P2096, Multiple codes or no codes displayed
Repairs/costs cited: Dealers initially perform software/ECM updates (Campaign 953, ECM replacement); some owners report multiple failed updates before acknowledging engine replacement is needed. Knocker rod and head gasket replacement attempted by independent mechanics with mixed/temporary results.
Recalls/TSBs owners mention: Campaign 953 software update offered; ECM replacement covered under warranty initially; claim denials citing lack of prior update completion or salvage title status.
Engine control module (ECM) failure
Check engine light comes on, sometimes followed by power loss, stalling, or misfiring. Diagnosis often points to faulty ECM that fails once or repeatedly even after replacement.
When: Varies; some owners report issues around 30k–62k miles; some experience recurrence after ECM replacement
Symptoms owners cite: Check engine light illumination; Engine misfiring and rough running; Loss of power during acceleration or highway merging; Delayed or intermittent start button response; Vehicle shaking or vibrating
Codes mentioned: Check engine light (underlying cause sometimes unidentified), P1326 or other fault codes
Repairs/costs cited: ECM replacement performed under warranty; owners report same failure recurring within 14,000 miles. Cost not cited; warranty typically covers replacement.
Recalls/TSBs owners mention: ECM replaced under warranty during early model years. Owners report warranty denial on second/replacement ECM failure.
Engine fire
Engine catches fire, often following stalling, smoke, or overheating. Two narratives explicitly describe vehicle engulfed in flames; fire department intervention required.
When: Occurs after or concurrent with stalling/loss of power; timing unpredictable
Symptoms owners cite: Smoke from underneath hood or engine bay; Engine stalling; Check engine light and multiple warning lights; Flames visible from under hood (in fire cases)
Codes mentioned: Multiple warning lights illuminated
Repairs/costs cited: Vehicle destroyed or severely damaged; no repair possible. Owners cite extreme financial loss and safety danger.
Recalls/TSBs owners mention: No manufacturer response documented for fire incidents; vehicles not covered under warranty for post-fire scenarios.
Oil leaks and internal pressure issues
Vehicle leaks oil from gaskets, seals, or internal engine components. Dealers replace gaskets and seals repeatedly without resolving underlying excessive oil consumption or blow-by issues.
When: Typically manifests in warranty period (1–2 years of ownership) at 30k–70k miles
Symptoms owners cite: Oil leaking visibly underneath vehicle; Need for multiple gasket and seal replacements; Internal pressure causing excessive blow-by; Low oil on dipstick despite no external leak visible after repairs
Codes mentioned: Oil pressure-related codes (if any)
Repairs/costs cited: Valve cover gasket, valve seal, and other seals replaced; some multiple times. Costs covered initially under warranty but ineffective. Independent mechanic identified internal pressure/blow-by as root cause not addressed by dealer.
Recalls/TSBs owners mention: Warranty coverage for gasket/seal replacement initially; denial if out of warranty or if oil consumption test deemed negative.
Turbo inlet duct detachment / separation
Air inlet duct connecting to turbo detaches or severs at point of attachment. Dealership deemed vehicle unsafe to drive; parts on national back order with no delivery date provided.
When: Reported at roughly 200 miles driven on a 2.0 turbo engine
Symptoms owners cite: 'Whooshing sound' during acceleration; Inlet duct physically detached or melted at turbo attachment
Repairs/costs cited: Replacement part required; Hyundai parts on national back order with no promised delivery date. Dealership indicated risk of total engine failure if object enters unattached turbo.
Recalls/TSBs owners mention: No manufacturer response documented; parts unavailable.
Synthesized from 412 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 7 most recent
I was driving 60mph with cruise on a state highway. When the car accelerated there was a noise I couldn't identify. I immediately pulled to the side of the road to investigate and the noise sounded like rocks grinding. I checked oil and it was full. When car was restarted the noise resumed. I turned off the car and it didn't start again. Towed to a garage and they said there were metal shavings…
The contact owns a 2015 Hyundai Sonata. The contact stated while driving 50 MPH, the vehicle stalled and failed to restart. No warning lights were illuminated. The vehicle was towed to the residence. The vehicle was not diagnosed nor repaired by an independent mechanic or dealer. The manufacturer was made aware of the failure. The failure mileage was approximately 174,000.
While driving the car started to putter and then stalled while on the way to work. The vehicle engine is shot I am told by the mechanic I have used for 10 years now. Called the dealership about the issue and was advised I could have it towed in at my expense and have them look at it at my expense since the car is out of warranty. The dealership I am sure will say it is not due to faulty parts or…
While traveling on the interstate, the car started shuddering. Pulled off and went to auto part store and they read the code #4 misfire. Took car to my mechanic and he said #4 cylinder was dead. Proceeded to take car to dealership and they said #4 cylinder had burn valve with hole in valve. We hey gave a quote for engine replacement. Took car back to my mechanic and he replaced engine at a cost…
Approximately five weeks ago, my 2015 Hyundai Sonata showed a check engine light. I took it into the dealer and paid a diagnostic fee which revealed the third cylinder misfire in the engine. I paid to have the engine cleaned yet the light continues to stay on and the car has been Running low on oil every time it gets checked the dealer states that the engine needs to be replaced
Tl* the contact owns a 2015 Hyundai sonata. While driving 60 MPH, the vehicle began to stall and the check engine warning indicator flashed. The contact pulled into a gas station and, upon depressing the accelerator pedal, the vehicle rumbled. The contact took the vehicle to an independent mechanic where the vehicle was diagnosed with a faulty engine knock sensor. The contact spoke with…
White driving either in motion or stopped behind a light, engine starts to shake and stall. This make the car share heavily and nudge forwards and backwards until the call stalls out. Then the dash gets lit up with all the check engine lights. Then, pressing the start button multiple times until the vehicles starts. The car does this every so often. You drive off, it shakes and stalls, it…
Had engine trouble with your 2015 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 2015 Hyundai Sonata?
It's a meaningful issue. 412 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?
Across the 199 complaints that reported odometer mileage, most engine failures cluster between 38,500 and 113,000 miles, with the median around 75,000. A quarter of owners report trouble before 38,500; a quarter make it past 113,000. Maintenance history matters more than the odometer alone — this is the reported failure window, not a guarantee.
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/2015/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.