P0306 on Hyundai: How to Diagnose & Fix
Cylinder 6 Misfire Detected
1 Hyundai model · 1 documented issue · 1 critical
P0306 on Hyundai by model: symptoms, diagnosis and fix
The Theta II GDI engine in 2014-2015 and 2018-2019 Tucson models is susceptible to connecting rod bearing failure caused by manufacturing debris restricting oil flow. This can lead to catastrophic engine seizure, often without warning. Under the Theta II engine class-action settlement, Hyundai extended the powertrain warranty to a Lifetime Warranty (Warranty Extension TXXI) for connecting rod bearing damage on vehicles that complete the Knock Sensor Detection System software update (Service Campaign 953).
Common Symptoms
- Metallic knocking from engine
- Engine stalling without warning
- Check engine light with P1326 code
- Loss of power while driving
- Excessive oil consumption
How to Fix
Check VIN for active recalls at NHTSA.gov. Ensure the Knock Sensor Detection System (KSDS) software update has been installed - this monitors for early signs of bearing failure and can put the engine in limp mode. If the engine has failed from connecting rod bearing damage after the KSDS update, Hyundai covers the short-block repair under the lifetime warranty extension. Out-of-warranty replacement runs $4,500-7,500. Use full synthetic 0W-20 oil and change every 5,000 miles.
Owner tips & cautions
- TipGet the KSDS software update immediately if not already done - it can detect bearing failure early and prevent catastrophic seizure
- WarningIf you hear any knocking noise, stop driving immediately. Continued driving can destroy the engine beyond repair
Sources for this issue (1)
P0306 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0306 mean on a Hyundai?
P0306 stands for "Cylinder 6 Misfire Detected." This code means the engine computer detected a misfire on cylinder 6 — that cylinder isn't burning its fuel-air mixture properly. The computer senses misfires by watching for tiny variations in crankshaft speed each time a cylinder should fire, and when cylinder 6 repeatedly fails to contribute, this code sets. You may feel a shake or stumble, especially at idle or under load, along with reduced power and possibly a flashing check-engine light, which signals a misfire severe enough to damage the catalytic converter. A misfire comes down to a problem with spark, fuel, or compression in that cylinder. On Hyundai it is documented across 1 model: Tucson.
What are the most common causes of P0306?
The most common causes of P0306 are: Worn or fouled spark plug on cylinder 6, Failed ignition coil for cylinder 6, Clogged, leaking, or failed fuel injector, Vacuum or intake air leak affecting that cylinder, Low compression (worn rings, burnt valve, head gasket), Damaged plug wire or coil connector, Carbon buildup or worn valvetrain components. The specific cause varies by vehicle.
How much does it cost to fix P0306 on a Hyundai?
Repair costs vary widely with the root cause and Hyundai model; each issue on this page carries its own estimate where one is published.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.