P0306: How to Diagnose & Fix — Cylinder 6 Misfire Detected
88 vehicles · 26 makes · $60-$25,000 repair
How to diagnose and fix P0306: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Hyundai Tucson · 2014–2019
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)
Porsche 911 · 2009–2019
The 991-generation 911 suffers from cylinder bore scoring where the Lokasil cylinder liners develop deep vertical scores, typically on cylinders 1 and 6. This is caused by inadequate oil supply to the cylinder walls during cold starts and short-trip driving. The issue results in excessive oil consumption and eventually requires engine rebuild or replacement.
Common Symptoms
- Excessive oil consumption (more than 1 quart per 1,000 miles)
- Blue or white smoke on cold start
- Rough idle when engine is cold
- Metallic rattling from engine
- Compression test showing low values on cylinders 1 or 6
How to Fix
Engine must be removed and disassembled. Scored cylinders are repaired by installing iron sleeves (LN Engineering Nickies) or replacing the cylinder block. Some owners opt for a used or rebuilt engine. Prevention: always warm the engine fully before spirited driving and avoid short trips.
Owner tips & cautions
- WarningWhen buying a used 991, always perform a leak-down and compression test before purchase. Bore scoring is extremely expensive to repair and often not covered under Porsche warranty after the initial period.
Sources for this issue (5)
- LN Engineering: What is Porsche Cylinder Bore Scoringmanufacturer
- LN Engineering: Identifying the Porsche Bore Scoring Problemmanufacturer
- The Drive: The Complete History and Current State of the Porsche Bore Scoring Issuemedia
- Porsche Club of America: Bore scoring and how to prevent itmanufacturer
- Flat 6 Innovations: Cylinder Bore Scoringmanufacturer
Honda Pilot · 2016–2022
Variable Cylinder Management (VCM) causes excessive oil consumption (1 quart every 1,000-1,500 miles), engine misfires, and fouled spark plugs. The reciprocating effect creates vacuum that pulls oil past piston rings. Leads to premature failure of spark plugs, catalytic converters, engine mounts, and cylinder walls. The 2013 VCM class-action settlement (8-year warranty extension) covered only 2009-2013 Pilots, not these model years.
Common Symptoms
- Excessive oil consumption (1 qt per 1,000-1,500 miles)
- Engine misfires (P0300-P0306 codes)
- Fouled spark plugs
- Rough idle or hesitation
- Check engine light
- Excessive engine vibration when VCM activates
- Blue smoke from exhaust
How to Fix
Disable VCM using aftermarket devices: VCMuzzler II ($81), VCMTuner II ($150-200), or S-VCM Controller ($180-250). Check oil level every 500-1,000 miles and top off as needed. Use synthetic 0W-20 oil. Replace spark plugs every 30k-50k miles instead of 100k. Severe cases may need engine rebuild ($4,000-$8,000).
Owner tips & cautions
- TipDisabling VCM reduces damage to engine mounts ($800) and minimizes transmission torque converter wear
- TipCheck oil level every 500-1,000 miles and keep 2-3 quarts of oil in vehicle for top-offs
- WarningDo not ignore excessive oil consumption - running engine low on oil can cause catastrophic engine failure
Sources for this issue (2)
Porsche Boxster · 2005–2012
Chrysler 300 · 2011–2023
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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?
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.
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?
Repair costs for P0306 range from $60 to $25,000, depending on the vehicle and root cause.
Which vehicles are affected by P0306?
Au7o has documented P0306 across 88 vehicle models from 26 manufacturers: Acura, Audi, BMW, Cadillac, Chevrolet, Chrysler, Dodge, Ford, GMC, Genesis, Honda, Hyundai, Infiniti, Jaguar, Jeep, Kia, Lexus, Lincoln, Mazda, Nissan, Porsche, RAM, Saturn, Subaru, Toyota, Volkswagen.
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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.