TECHNICAL SERVICE BULLETIN: TRANSMISSION FLUID APPLICATION GUIDE - This bulletin has been revised to include additional information. New/revised sections of this bulletin are indicated by a black bar in the margin area. This bulletin provides information relating to the correct transmission fluid type and fill quantity requirement for each Kia model. A flush is required ONLY when a transmission is replaced, and the transmission oil cooler is transferred to the new transmission.
full bulletin at NHTSA ↗2021 Kia K5 powertrain problems
moderate Owners of the 2021 Kia K5 have filed 16 NHTSA complaints about the powertrain at roughly $2,500 to repair (U.S. federal records, as of August 2026). Source: NHTSA Office of Defects Investigation. See powertrain across all vehicles →
Complaints
16
Recalls
0
Avg fix
$2,500
| Model year | powertrain complaints |
|---|---|
| 2021 K5 (this page) | 16 |
| 2022 K5 | 18 |
| 2023 K5 | 11 |
| 2024 K5 | 3 |
| 2025 K5 | 6 |
What stands out
Among the 5 model years of Kia K5 in our records for powertrain problems, this one ranks #2 by owner-complaint volume.
No new NHTSA powertrain complaint has been filed on this vehicle in over 5 years — the issue may be aging out of the active population.
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.
TECHNICAL SERVICE BULLETIN: 8-SPEED DUAL CLUTCH TRANSMISSION EOP SENSORLESS LOGIC IMPROVEMENT - This bulletin has been revised to include additional information. New/revised sections of this bulletin are indicated by a black bar in the margin area. This bulletin provides information to improve the Electric Oil Pump ‘EOP’ operation logic of the automatic transmission ‘A/T’ on some 2021-2023MY Sorento (MQ4a) vehicles produced from September 9, 2020 through December 29, 2023 and 2021-2023MY K5 (DL3a) vehicles produced from March 24, 2020 to December 18, 2023, equipped with a 2.5L T-GDI Theta III engines and 8-Speed Dual Clutch Transmissions (DCT). The affected vehicles may exhibit abnormal/hars
full bulletin at NHTSA ↗TECHNICAL SERVICE BULLETIN: PRECAUTIONS FOR TRANSMISSIONS WITH ISG/EOP - This bulletin provides information related to the replacement or servicing of transmission assemblies on all Kia vehicles equipped with Idle-Stop-Go (ISG) and High-Flow Electric Oil Pump (HF EOP). The HF EOP protective connector cover may NOT have been installed on a new or remanufactured transmission during assembly. The HF EOP connector may become contaminated with debris during shipping and/or with oil/coolant during installation.
full bulletin at NHTSA ↗TECHNICAL SERVICE BULLETIN: 8-SPEED DUAL CLUTCH TRANSMISSION EOP SENSORLESS LOGIC IMPROVEMENT - This bulletin has been revised to include additional information. New/revised sections of this bulletin are indicated by a black bar in the margin area. This bulletin provides information to improve the Electric Oil Pump ‘EOP’ operation logic of the automatic transmission 'A/T’ on some 2021-2023MY Sorento (MQ4a) vehicles produced from September 9, 2020 through December 29, 2023 and 2021-2023MY K5 (DL3a) vehicles produced from March 24, 2020 to December 18, 2023, equipped with a 2.5L T-GDI Theta III engines and 8-Speed Dual Clutch Transmissions (DCT). The affected vehicles may exhibit abnormal/hars
full bulletin at NHTSA ↗TECHNICAL SERVICE BULLETIN: 8-SPEED DUAL CLUTCH TRANSMISSION EOP SENSORLESS LOGIC IMPROVEMENT - This bulletin provides information to improve the Electric Oil Pump ‘EOP’ operation logic of the automatic transmission ‘A/T’ on some 2021-2023MY Sorento (MQ4a) vehicles produced from September 9, 2020 through December 29, 2023 and 2021-2023MY K5 (DL3a) vehicles produced from March 24, 2020 to December 18, 2023, equipped with a 2.5L T-GDI Theta III engines and 8-Speed Dual Clutch Transmissions (DCT).
full bulletin at NHTSA ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
The failure pattern owners describe
The 2021 Kia K5 powertrain complaints center on transmission and engine failures that catch owners off-guard. Multiple owners report sudden, complete loss of power while driving—the transmission simply quits, forcing them to coast to a shoulder or stop. This happened to one owner twice before 17,000 miles. Others describe transmission jerking, sputtering, and grinding when shifting gears, or slip and hesitation during acceleration that won't respond to the pedal. One owner's transmission failed within 5 days of purchase; another's required replacement at just over 4,600 miles due to loss of motive power with no prior warning signs, though check-engine lights and pull-over warnings appeared just before shutdown.
Engine issues also appear: one owner experienced a broken camshaft with metal debris scattered through the engine at 1.5 years of ownership, requiring complete engine replacement. A vacuum pump failure on the same vehicle left brakes dangerously hard to apply. The oil warning light never came on despite eventual catastrophic engine damage. One owner reports a persistent antifreeze smell from the engine bay that dealers claim is normal across the model line. Owners also cite transmission shifting delays that last seconds after releasing the accelerator, and slipping at both low and highway speeds. A delayed-repair case involved a transmission issue held under recall for months without resolution or transparency from the dealership.
Same Kia K5 powertrain reports on nearby years: 2022 · 2023
Failure modes owners describe
Transmission failure - complete loss of power
Sudden, complete loss of motive power while driving, requiring coasting to a stop. No warning signs before failure. Occurs without prior symptoms. Owners report this is a known issue on 2021+ K5 GT 2.5L and similar Hyundai models with same engine/DCT combo (Hyundai Recall #236 referenced).
When: First occurrence at 4,600 miles (6/13/2021); second at 16,600 miles (9/7/2022). One owner reports it happened twice in six months.
Symptoms owners cite: Complete loss of power during normal highway driving; Vehicle must coast to a stop; Check engine light and pull-over warning illuminate just before failure; Loss of motive power occurs suddenly with no prior warning
Repairs/costs cited: Transmission replaced at dealership both times by Kia technicians.
Recalls/TSBs owners mention: Hyundai Recall #236 exists for same engine/DCT combination in Hyundai vehicles; appears same issue affects 2021+ Kia K5 GT 2.5L and 2021+ Kia Sorento.
Transmission shifting delays and sluggish acceleration
Delayed gear shifts during acceleration, with engine remaining revved for several seconds after driver stops accelerating before RPMs return to normal. Presents as sluggish or hesitant throttle response. Ongoing for months with no resolution from dealership.
When: Occurring for approximately 6 months prior to complaint (as of April 2023)
Symptoms owners cite: Shifting delays when accelerating; Engine remains revved up for several seconds after stopping acceleration; Sluggish or delayed acceleration response; RPM takes extended time to return to idle
Repairs/costs cited: Dealership claimed no issues reported despite owner reporting problem twice.
Transmission jerking and sputtering during gear shifts
Vehicle sputters and jerks during transmission downshifts, particularly when shifting from 1st to 2nd and 2nd to 3rd gear. Accompanied by grinding sound from transmission. No warning lights present.
When: At approximately 98,000 miles
Symptoms owners cite: Sputtering while shifting gears; Jerking motion during gear transitions; Grinding sound from transmission; No warning lights illuminated
Codes mentioned: Erratic gear shift (diagnostic description from dealer)
Repairs/costs cited: Vehicle diagnosed but not repaired by dealer.
Transmission slip during acceleration
Engine revs and transmission gears fail unexpectedly while accelerating, with vehicle unable to accelerate as intended despite pressing accelerator. Occurs at low speeds. No warning lights. One owner reports transmission slip during both stop-and-go and highway speeds.
When: One incident at 15-20 MPH; another owner experienced it twice in six months with no mileage stated
Symptoms owners cite: Engine revving without corresponding acceleration; Unexpected transmission gear failure; Vehicle fails to accelerate despite pressing accelerator pedal; Transmission slip at low and highway speeds; Jerking as transmission tries to accelerate
Repairs/costs cited: No repairs performed; vehicle parked due to safety concerns.
Transmission fluid leak requiring replacement within days of purchase
Transmission fluid leak discovered while vehicle parked within 5 days of new car purchase. Required complete transmission replacement.
When: Within 5 days of new vehicle purchase
Symptoms owners cite: Transmission fluid leak discovered on parked vehicle
Repairs/costs cited: Transmission required total replacement.
Broken camshaft with engine metal debris
Vacuum pump failure leading to no vacuum to brake booster; subsequent inspection revealed broken camshaft with metal pieces inside engine. Required complete engine replacement. Owner had no prior warning despite 1.5 years ownership; oil warning light never illuminated.
When: At 1.5 years ownership; triggered during highway driving with hard brakes and service light
Symptoms owners cite: Extremely hard brake pedal; Service engine light illumination; No vacuum to brake booster; Broken camshaft; Metal debris found in engine
Repairs/costs cited: Engine required complete replacement. Oil light never activated despite eventual engine failure.
Strong antifreeze smell from engine bay
Persistent and strong antifreeze odor from under the hood. Dealer claims odor is normal and present across multiple model years of this vehicle line. Owner disputes this as unhealthy and believes recall is needed.
When: Noticed shortly after purchase (3/1/25)
Symptoms owners cite: Very bad antifreeze smell under hood
Recalls/TSBs owners mention: Dealer states odor is normal across all model years of this car line; owner disputes this assessment.
Synthesized from 16 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 1 most recent
Transmission requires total replacement within 5 days of purchase of new car. Vehicle was parked when transmission fluid leak was discovered. It was driven back to the dealer, which is nearby, but this experience has shaken our faith in the safety and build quality of this 2021 Kia k5 gt-line.
Had powertrain trouble with your 2021 Kia K5?
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 2021 Kia K5?
It's a documented issue but not catastrophic. 16 complaints have been filed. Repairs average $2,500 and most owners catch it before it causes a breakdown.
At what mileage does the powertrain typically fail?
Based on the 16 complaints filed, powertrain issues most often appear around 80,006 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 $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/2021/Kia/K5.
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.