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 ↗2021 Hyundai Tucson engine problems
severe Owners of the 2021 Hyundai Tucson have filed 29 NHTSA complaints about the engine at roughly $3,100 to repair (U.S. federal records, as of August 2026). Source: NHTSA Office of Defects Investigation. See engine across all vehicles →
Complaints
29
Recalls
0
Avg fix
$3,100
| Model year | engine complaints |
|---|---|
| 2017 Tucson | 436 |
| 2018 Tucson | 160 |
| 2019 Tucson | 133 |
| 2020 Tucson | 56 |
| 2021 Tucson (this page) | 29 |
| 2022 Tucson | 55 |
| 2023 Tucson | 8 |
| 2024 Tucson | 8 |
2fires
2injuries
When does it fail?
Of the 29 engine complaints filed for the 2021 Hyundai Tucson, here's the actual mileage breakdown — failures cluster heaviest at 25,000-50,000 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 39% of every owner complaint on file for this vehicle — the dominant problem area across 4 categories tracked.
Owners have filed 29 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 ↗Certain 2019 – 2020 model year Santa Fe, 2017 – 2018 model year Santa Fe Sport, 2015 – 2019 model year Sonata, and 2018 – 2021 model year Tucson vehicles may exhibit elevated engine-out emissions. Hyundai is conducting a service campaign to update the Engine Control Module (ECM) Software for vehicles equipped with the (2.4 GDI) Theta II engine to improve engine combustion and fuel trim adaptations.
full bulletin at NHTSA ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
The failure pattern owners describe
The 2021 Hyundai Tucson engine cluster shows a pattern of repeated stalling and power loss tied to knock-sensor faults (P1326 code). Owners describe the vehicle entering limp mode without warning—suddenly restricting speed to 7–50 MPH—during highway driving, merging, and traffic situations. Some instances occur 55 days into ownership; others recur across 15,000 to 124,500 miles. Pre-failure signs include declining fuel economy, hesitations through the accelerator pedal, and decreasing power in acceleration days or weeks before a stall event.
Excessive oil consumption is widespread, with owners reporting rapid dipstick depletion and needing frequent top-ups between service intervals (roughly every 1,500 miles). One owner reports three catalytic converter replacements by 31,000 miles and states a dealer told them to return only when the engine fails, despite proper maintenance.
Two engine fire incidents occurred at low speeds (5 and 10 MPH), with flames exiting the hood and A/C vents. One fire caused injury when an occupant fell during evacuation.
Dealer repair attempts include knock-sensor replacements (sometimes 2–4 times), spark plugs, catalytic converters, ECM updates, and coil replacements—yet failures reoccur in nearly every case. Hyundai's recall Campaign 966 (knock sensor) has not resolved the underlying issue. Some owners report warranty denials citing maintenance records or the vehicle not qualifying for recall, despite matching failure descriptions. Engine replacement has been recommended but often denied or indefinitely delayed.
Same Hyundai Tucson engine reports on nearby years: 2018 · 2019 · 2020 · 2022
Failure modes owners describe
Engine Stalling / Sudden Power Loss (Limp Mode)
Engine loses power, enters limp mode, and restricts vehicle to 7–50 MPH. Occurs while driving at highway speeds, traffic, or merging. Often preceded by flashing check-engine light; no warning lights beforehand in some cases.
When: Multiple instances from purchase date; at 72,021 miles, during early ownership (55 days reported), recurring through 124,500 miles
Symptoms owners cite: Flashing check engine light or sudden illumination; RPM spikes followed by power loss; Vehicle restricted to 3,000–20 MPH max speed; Unable to exceed 2,000–3,000 RPM; Hesitation and pulsing through accelerator pedal days/weeks prior; Declining fuel economy before failure
Codes mentioned: P1326, P0300 (implied by knock sensor complaints)
Repairs/costs cited: Dealers replaced knock sensors (sometimes 2–3 times), spark plugs, catalytic converters, updated ECM. Failures recurred despite repairs. One owner reports rod bearing replacement and engine replacement attempted but failure reoccurred. Engine replacement denied or delayed by manufacturer in several cases.
Recalls/TSBs owners mention: Hyundai recall Campaign 966 (May 2022, knock sensor update). Some owners denied coverage citing lack of maintenance records or vehicle not qualifying for recall. Extended 15-year/150,000-mile warranty mentioned in one complaint but Hyundai refused replacement. Hyundai advised continued operation pending further failure.
Engine Fire
Engine compartment fire with flames exiting hood and A/C vents while driving at low speed (5 MPH driveway, 10 MPH on road). Vehicle became total loss. One incident caused injury (flash burn, back pain from fall during evacuation).
When: At approximately 25,000 miles (driveway fire); 65,000 miles (clicking sound before fire on low-speed drive)
Symptoms owners cite: Steam coming from under hood with no warning light; Abnormal clicking sound under hood; White smoke turning black; Flames from engine compartment and A/C vents; Fire engulfed vehicle
Repairs/costs cited: Vehicles totaled by insurance. Fire department extinguished fires. Insurance technician determined fire originated in engine compartment.
Recalls/TSBs owners mention: One case: manufacturer notified and case opened; no further information. Second case: manufacturer not notified.
Excessive Oil Consumption
Engine consumes oil rapidly, requiring frequent top-ups between service intervals (full dipstick depletion every ~1,500 miles). Dealers performed oil consumption tests; results varied. One owner reports 3 catalytic converter replacements by 31,000 miles. Engine oil pressure warning lamp illuminates.
When: At 31,000 miles (3 converters replaced); persisting over 3+ years in one case; 89,000 miles in another
Symptoms owners cite: Oil level drops rapidly (dipstick shows no oil); Engine oil pressure warning light illuminates; Check engine light illuminates; Frequent need to top up oil between changes; Risk of engine seizure mentioned; Related ignition coil and spark plug failures
Codes mentioned: P1326 (knock sensor code linked in one case)
Repairs/costs cited: Oil consumption tests performed; some passed, others led to engine-replacement diagnosis. Dealers initially told one owner to return 'when the engine fails' despite excessive consumption. Engine replacement recommended in at least one case but claim denied. Multiple catalytic converter replacements; one owner had 3 by 31,000 miles.
Recalls/TSBs owners mention: No warranty coverage offered in some cases despite documented recalls. Hyundai advised one owner no assistance after being notified.
Knock Sensor Faults (P1326 Code)
P1326 diagnostic code triggers limp mode, check-engine light (often flashing), and severe power loss. Code reported as 'known Hyundai defect' by owners. Related to recall campaign but repairs remain non-permanent.
When: Recurring at 15,000 miles, 17,000 miles, 41,000 miles, 90,000 miles in one vehicle; incidents from 2022 onward
Symptoms owners cite: Flashing check engine light (P1326 code); Vehicle enters limp mode; Power loss; max speed 20–30 MPH; Cannot exceed 2,000 RPM; Occurs during acceleration from stop or in traffic
Codes mentioned: P1326
Repairs/costs cited: Knock sensor replaced 1–4 times per vehicle; failures recurred. ECM updates attempted. One dealer attempted $225 diagnostic fee despite code being 'known Hyundai defect' covered under recall.
Recalls/TSBs owners mention: Recall Campaign 966 (knock sensor update, May 2022). Hyundai advised continued operation unless failure occurs again; no permanent fix identified. Some owners told vehicle does not qualify for recall despite matching failure pattern.
Rod Bearing / Internal Engine Damage
Abnormal rattling or knocking sound from engine; engine diagnosed as requiring bearing or full engine replacement. One owner reports bearing replacement that recurred; others denied coverage citing maintenance records or non-qualification for recall despite matching symptoms.
When: At 124,500 miles (rattling, abnormal sound); 60,000 miles (knock sensor diagnosis leading to engine replacement denial)
Symptoms owners cite: Abnormal rattling sound from engine; Knocking noise increasing with RPM; Vehicle fails to accelerate; Shut-off at 35–45 MPH without warning; Oil light and check engine light
Repairs/costs cited: Rod bearing and engine replacement diagnosed at one dealer; attempted repair but failure recurred. Coils replaced at another dealer without fixing issue. Independent mechanic determined engine was at fault. Another owner at 60,000 miles denied repair under unknown recall due to maintenance records.
Recalls/TSBs owners mention: No additional assistance provided in one case after manufacturer contact.
NOX Sensor Failures (Limp Mode)
NOX sensor fails causing limp mode and severe deceleration from 65 MPH to 7 MPH. Multiple failures within days of ownership in one case.
When: At 28,944 miles, within days of certified-vehicle purchase; recurring three times within weeks
Symptoms owners cite: Vehicle enters limp mode without warning; Sudden deceleration from 65 MPH to 7 MPH; Flashing check engine light
Repairs/costs cited: NOX sensor replaced twice and catalytic converter replaced; failures recurred within days. Vehicle traded in. Owner had to trade vehicle rather than continue repair cycle.
Recalls/TSBs owners mention: Manufacturer notified; no further details provided.
Synthesized from 29 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 9 most recent
Oil light comes on between changes at about 1500 miles before needing one, oil does not show on dipstick and have to repeatedly put on in engine. Chance of engine seizing or jumping time.
The contact owns a 2021 Hyundai Tucson. The contact stated while driving at an undisclosed speed, the accelerator pedal was depressed, but the vehicle failed to accelerate as intended. The check engine warning light was illuminated. The contact stated that the vehicle failed to exceed 20 MPH. The contact stated that the failure had occurred while driving on a busy highway. The contact safely…
We were driving and the engine light started flashing and buckling. The vehicle had been properly maintained with oil changes. We have oil changes receipts from our mechanic. Hyundai refuses to cover it under their warranty even though there are documented issues with the make and models of 2021 Hyundai Tuscons.
Engine started making a knocking sound, then the oil light came on followed by the check engine light. Accelerates and decelerates on its own. Was forced to immediately pull over across three lanes on Interstate 95. It’s been over two weeks and I’ve yet to hear if Hyundai is going to cover a replacement engine. However, what happened is exactly what they have listed on their website ️ What to…
My family’s safety is at serious risk with my 2021 Hyundai Tucson, which I’ve owned only 55 days. This vehicle has stalled three times while driving, putting me and my two young children in immediate danger. Each time, the car operated normally until a flashing engine light appeared, RPMs spiked, and the vehicle suddenly lost all power—entering “limp mode” and unable to exceed 3,000 RPM or 50…
September 15, 2023 while driving on the expressway my engine light came on. Vehicle towed to World Hyundai dealership and it was diagnosed as engine seized.
My check engine light came on in the vehicle and immediately the acceleration declined and I wasn’t able to go above 50 mph. I brought the vehicle to the dealership to which the code 1326 came up. I was told it is a rod bearing engine failure and I need a new engine for the vehicle. I was also told my vehicle doesn’t qualify for the recall already made for this damage and code number.
When going through Auburn, AL with speed limit of 70 mph my car engine started blinking on and off then my car dropped down only allowing me to go 60 Mph.
The contact called on behalf of his girlfriend who owned a 2021 Hyundai Tucson. The contact stated while driving 5 MPH in the driveway, there was steam coming out from under the hood. There was no warning light illuminated. The contact parked the vehicle. The contact stated that as he opened the hood, flames came out. The contact's girlfriend also saw flames coming out of the A/C vents. The…
Had engine trouble with your 2021 Hyundai Tucson?
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 Tucson?
It's a meaningful issue. 29 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 29 complaints filed, engine issues most often appear around 62,464 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/Tucson.
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.