This TSB provides a procedure to diagnose and replace, if necessary, an automatic transmission with Incorrect Ratio DTC (transmission clutch slip in gear above limit) listed on Page 2.
full bulletin at NHTSA ↗2018 Hyundai Sonata powertrain problems
severe Owners of the 2018 Hyundai Sonata have filed 36 NHTSA complaints about the powertrain, typically surfacing around 47,575 miles at roughly $2,500 to repair (U.S. federal records, as of July 2026). Source: NHTSA Office of Defects Investigation. See powertrain across all vehicles →
Failure mileage
Complaints
36
Recalls
0
Avg fix
$2,500
| Model year | powertrain complaints |
|---|---|
| 2014 Sonata | 51 |
| 2015 Sonata | 125 |
| 2016 Sonata | 58 |
| 2017 Sonata | 53 |
| 2018 Sonata (this page) | 36 |
| 2019 Sonata | 8 |
| 2020 Sonata | 23 |
| 2021 Sonata | 21 |
| 2022 Sonata | 23 |
2crashes
1fire
1injury
What stands out
Owners have filed 36 powertrain 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 powertrain 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.
If you are servicing an 8-speed vehicle with a âCheck Engineâ light on and one or more of the DTC listed, follow the service procedure and replace the related solenoid and harness.
full bulletin at NHTSA ↗Hyundai has launched an anti-theft software upgrade and window decal campaign (Campaign 993), combined with an anti-theft steering wheel lock campaign (Campaign P32), in response to an increase in thefts of certain 2011-2022MY Hyundai vehicles not equipped with engine immobilizers targeted through social media. For certain vehicles that cannot be updated with the software (Campaign 993), Hyundai is offering customers steering wheel locks at the dealer (Campaign P32). This Dealer Best Practices Guide provides information to assist dealership personnel with customer questions relating to the immobilizer software upgrade, window decals and steering wheel lock ant-theft solutions available from
full bulletin at NHTSA ↗If you are servicing an applicable vehicle with a âCheck Engineâ light on and one or more of the DTC listed below, follow the repair procedure and replace the related input/output speed sensor and harness.
full bulletin at NHTSA ↗Certain vehicles (listed below) equipped with 7-speed Double Clutch Transmissions (DCT) may exhibit abnormal vibration at low speeds. This bulletin outlines the procedures for diagnosing clutch judder, updating the Transmission Control Unit (TCU) with revised logic, and/or replacing the Double Clutch.
full bulletin at NHTSA ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
The failure pattern owners describe
The 2018 Sonata powertrain failures center on internal engine degradation, excessive oil consumption, and electrical control issues. The dominant problem is rod bearing wear in the Theta II engine, causing piston rattle, knocking, misfiring, and eventual seizure. Owners report the engine consuming 1 quart of oil per week to every other week with no external leak, spark plugs fouled with oil, and exhaust smoking. Engine failures happen without advance warning—the check engine light comes on only as the engine fails. Sudden shutdowns occur at highway speeds, creating hazard situations.
Hyundai issued Campaign 953 (knock sensor update) intended to trigger limp mode as an early warning, but owners report the vehicle enters limp mode repeatedly even after knock sensor replacement, capping RPMs at 2,000 and making the car nearly undrivable. Service departments acknowledge the rod-bearing defect and agree replacement is needed, but Hyundai Corporate denies coverage without owner-paid diagnostic tests ($300–$500 each). One dealership documented an alternator bracket failure due to inadequate aluminum design, with technicians noting multiple similar cases.
Transmission issues include hard downshifts at low speeds, hesitation upon acceleration, and shuddering. The dual-clutch automatic exhibits a 3-second hesitation from stopped position that service departments claim is unfixable. Starter failure occurred as early as 50,000 miles. Overall, owners face recurring repair costs of $300–$600 per incident for coil packs, spark plugs, and sensors, with the underlying engine defect unresolved and manufacturer warranty denial standard practice.
Same Hyundai Sonata powertrain reports on nearby years: 2015 · 2016 · 2017 · 2020 · 2021
Failure modes owners describe
Rod bearing failure / internal engine damage
Rod bearings wear prematurely, leading to piston rattle, knocking, misfiring, and eventual complete engine seizure. Damage includes cracked pistons, zero compression in affected cylinders, and internal component failure. This is the dominant failure mode across complaints, often associated with excessive oil consumption and the Theta II engine family.
When: Mileage range 5,400 to 107,000 miles; symptoms progressive over months to years
Symptoms owners cite: Loud knocking or rattling at cold start or under load; Engine misfiring, hesitation, shuddering, and vibration; Flashing check engine light; limited engine power / limp mode; Complete engine shutdown or loss of power while driving; Oil consumption of 1 quart per week to 1 quart every other week; Fouled spark plugs with oil scoring; White, gray, or black exhaust smoke; Oil discharge from exhaust pipe
Codes mentioned: P1326 (engine knock sensor), P2600 (HEV / hybrid system fault), Engine misfire codes
Repairs/costs cited: Owners report dealer recommendations for engine replacement; however, Hyundai Corporate often refuses coverage without expensive diagnostic tests (oil consumption test, rod-bearing test, engine compression test) that can cost $300–$500+ per test. Some dealers approved one-time combustion chamber cleaning as a temporary measure. Full engine replacement costs not specified but implied to be manufacturer responsibility under federal recall.
Recalls/TSBs owners mention: Campaign 953 Product Improvement (knock sensor update); federal recall for rod-bearing failure affecting 2011–2019 Theta II engines; class-action lawsuits referenced. Hyundai advised some owners to continue driving 'until engine seizes' or 'loud knocking noise' heard, despite technicians agreeing replacement needed. Warranty denial cited on basis of insufficient diagnostic evidence or 'maintenance neglect,' despite normal maintenance records.
Excessive oil consumption without external leak
Engine consumes oil internally at abnormal rates without visible external leakage, indicating piston ring, cylinder wall, or valve seal failure. Consumption accelerates over vehicle ownership from monthly to weekly rates.
When: Begins early in ownership; worsens progressively over 1–3 years
Symptoms owners cite: Oil level drops 1 quart per week to 1 quart every other week; No visible oil puddles under vehicle; Fouled spark plugs with oil residue; Engine smoking under hood; Misfiring and hesitation correlating with oil level drop
Repairs/costs cited: Dealers performed oil gasket replacement (fuel filter gasket recalls), combustion chamber cleaning, and advised oil consumption tests at $300+ out of pocket. Owners report bearing the cost despite suspecting manufacturer defect.
Recalls/TSBs owners mention: Hyundai service departments denied warranty coverage on oil consumption repairs, citing need for owner-paid diagnostic testing. One dealer offered one-time combustion chamber cleaning after 1,000-mile test drive to evaluate improvement.
Engine stall and loss of power while driving
Engine suddenly shuts down or loses all power while operating at highway or city speeds, without prior warning lights. Occurs at idle, during acceleration, or while cruising. Vehicle becomes undrivable until towed or limped home.
When: Incidents reported at mileages 50,000–107,000; timing unpredictable
Symptoms owners cite: Sudden engine shutdown with no restart; Loss of motive power at 45–80 mph; Check engine light illuminates (often flashing) coincident with failure; Stalling at traffic lights or during acceleration; Sputtering before shutdown
Codes mentioned: Check engine light (specific codes not always recorded)
Repairs/costs cited: Dealers unable to replicate or diagnose in most cases; some suspected starter relay, alternator, or fuel pump issues. One vehicle diagnosed with zero compression in cylinder 3 and cracked piston requiring engine replacement. Repairs range $300–$600 per incident for coil packs, spark plugs, and sensor replacement.
Recalls/TSBs owners mention: No recalls specifically for stall events noted in complaints; some cases tied to knock sensor updates.
Limp mode activation with reduced power
Vehicle enters limp mode (reduced RPM limit, typically 2,000 RPM max) triggered by knock sensor faults or engine control issues. Can occur repeatedly even after knock sensor replacement or software updates.
When: Recurring events; some triggered immediately after Campaign 953 recall update (within 50 miles)
Symptoms owners cite: Sudden entry into limp mode; RPM capped at ~2,000; Hard jerking and shuddering when attempting acceleration; Check engine light illumination; Vehicle nearly undrivable, hazardous in traffic; Loud noises from engine
Codes mentioned: P1326 (knock sensor), Related to rod-bearing wear detection
Repairs/costs cited: Knock sensor replacement $300–$500; software re-flashing attempted but often does not resolve recurring activation. Campaign 953 intended to trigger limp mode on vehicles with rod-bearing wear, but false positives and recurrence reported.
Recalls/TSBs owners mention: Campaign 953 Product Improvement issued to activate limp mode as early warning of rod-bearing wear. However, dealers report difficulty distinguishing legitimate faults from software anomalies; some tech bulletins (TBS #19-01-002) reference engine replacement or wiring harness repair.
Transmission hard downshift and shuddering
Automatic transmission executes abrupt downshifts accompanied by jerking or shuddering, particularly when braking at low speeds. Some narratives describe dual-clutch transmission behavior mimicking manual clutch operation.
When: Reported at low mileage after purchase; onset as early as 2018 model year purchase
Symptoms owners cite: Hard, jolting downshift when applying brake at 10–15 mph; Engine and transmission shuddering or stuttering during deceleration; Hesitation upon acceleration from stop with 3-second delay before full throttle response; Shuddering during acceleration on hills or in moving traffic
Repairs/costs cited: No repairs documented in complaints; service departments noted numerous customer complaints but indicated no factory fix available. Described as design characteristic of dual-clutch transmission that owners either 'love or hate.'
Recalls/TSBs owners mention: No TSBs, recalls, or fix offered; service advisors disclosed to some customers that issue is known but unfixable.
Alternator bracket failure and detachment
Aluminum alternator bracket fails, allowing alternator to separate from engine mounting. Results in sudden loss of electrical power and charging.
When: At least one incident reported; dealership noted 3 similar cases in-house
Symptoms owners cite: Sudden loss of electrical power while driving; All dashboard lights illuminate; Loss of vehicle control; Vehicle immobilized on roadside
Repairs/costs cited: Alternator replacement required; dealership technicians identified systemic design flaw in aluminum bracket.
Recalls/TSBs owners mention: Dealership reported issue to manufacturer; no recall or design change communicated. Described as known systemic defect in alternator bracket design using inadequate aluminum material.
Starter failure and premature wear
Starter motor fails or wears out prematurely, well before typical service life expectancy.
When: Reported at less than 50,000 miles
Symptoms owners cite: Vehicle fails to start or difficulty starting; Possible starter relay issues noted in one complaint
Repairs/costs cited: Starter replacement performed; owner noted premature failure compared to typical 150,000+ mile lifespan on other manufacturers' vehicles.
Check engine light and warning system malfunction
Check engine light fails to illuminate in advance of serious engine problems, or illuminates too late to allow safe pull-over. One complaint also included non-functioning seatbelt warning.
When: Throughout ownership
Symptoms owners cite: No check engine light prior to sudden engine failure at highway speeds; Check engine light illuminates only as engine is failing; HEV (hybrid/engine control module) warning message appearing intermittently; Multiple distracting noises from control module warnings
Codes mentioned: P2600 (HEV / hybrid system malfunction)
Severe oil leak
Oil leaks into oil pan at abnormal rate, requiring frequent topping off between service intervals.
Symptoms owners cite: Rapid oil level drop; Frequent oil pan refilling needed
Repairs/costs cited: Requires frequent maintenance and oil additions
Synthesized from 36 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 2 most recent
When my car suddenly stopped on the highway, I encountered an issue with the “body control module.” The car wouldn’t start, and the key fob was ineffective. Additionally, the airbags stopped working. I don’t recall all the details, but I was unsure of where to report the dangerous vehicle. I’ve noticed several other Hyundai owners complaining about this issue, where their cars suddenly stop in…
While driving on the highway, my 2018 Hyundai Sonata experienced sudden loss of engine power and became undrivable. The failure occurred without warning at approximately 86,500 miles. At the time of the incident, there were two children in the vehicle, and the breakdown occurred at night in cold temperatures (approximately 20°F). An authorized Hyundai dealership later diagnosed zero compression…
Had powertrain trouble with your 2018 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 powertrain problem on the 2018 Hyundai Sonata?
It's a meaningful issue. 36 complaints have been filed and the failure mode causes operational problems for owners. Repairs average $2,500.
At what mileage does the powertrain typically fail?
Across the 10 complaints that reported odometer mileage, most powertrain failures cluster between 5,560 and 86,000 miles, with the median around 47,575. A quarter of owners report trouble before 5,560; a quarter make it past 86,000. 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 $2,500 for powertrain 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 powertrain?
No active recalls currently cover powertrain 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/2018/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.