P0306: How to Diagnose & Fix — Cylinder 6 Misfire Detected
104 vehicles · 26 makes · $50-$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 Sonata · 2011–2019
The Theta II engine can seize due to metal debris blocking oil flow to connecting rod bearings. Hyundai issued recalls and extended warranties. Affected engines may need replacement.
Common Symptoms
- Knocking noise from engine
- Engine stalling
- Check engine light
- Loss of power
- Engine seizure
How to Fix
Check VIN for active recalls - Hyundai provides free engine replacement for affected vehicles. Install the knock sensor detection system (KSDS) software update that monitors for bearing wear. Change oil every 5,000 miles. If engine fails and under warranty, replacement is free. Out of warranty replacement: $4,000-8,000.
Owner tips & cautions
- TipDIY repairs can save significantly - dealer charges $4,000-8,000 but DIY costs are typically 50-70% less
- WarningThis is a high-severity issue - ignoring it can lead to costly repairs or safety concerns. Address it promptly.
- TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
Sources for this issue (1)
- NHTSA Recall 17V-224recall
Mazda MX-5 Miata · 1999–2005
The NB Miata (1999-2005) crankshaft position sensor (CPS) is a known failure point. The sensor deteriorates from engine heat, causing intermittent stalling, no-start conditions, and random misfires. Failure is often heat-related - the car runs fine when cold but stalls or dies after reaching operating temperature.
Common Symptoms
- Engine stalls when hot, restarts after cooling down
- Intermittent no-start condition (cranks but does not fire)
- Random misfires and rough running at operating temperature
- Check engine light with P0335 (CPS circuit) code
How to Fix
Replace crankshaft position sensor with OEM Mazda unit (N3A1-18-221A). Aftermarket sensors (Delphi, Dorman) have higher failure rates on this application. The sensor is located on the rear of the engine block near the flywheel.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Mazda BP4W-18-221B crankshaft position sensorOEMMazda BP4W-18-221B
Confirm VIN before ordering; thi
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Owner tips & cautions
- TipCarry a spare CPS in the trunk - they fail without warning. Miata.net CPS mega-thread
- TipRoute sensor wiring away from exhaust manifold heat to extend sensor life
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
Hyundai Tucson · 2011–2019
Honda Pilot · 2016–2022
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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 $50 to $25,000, depending on the vehicle and root cause.
Which vehicles are affected by P0306?
Au7o has documented P0306 across 104 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.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.