P0306 on Ford
Cylinder 6 Misfire Detected
P0306 on Ford vehicles indicates cylinder 6 misfire detected. Au7o has documented this code across 4 Ford models — most commonly on Bronco Sport, Crown Victoria, Expedition. 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. Typical repair costs on Ford range from $150 to $7,500, depending on the specific model and root cause.
Common Causes of P0306
- •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
P0306 on Ford by Model
Ford Bronco Sport(1 issue)
- 1.5L EcoBoost 3-Cylinder Coolant Loss and Engine Failure2021-2024
The 1.5L EcoBoost 3-cylinder engine in 2021-2024 Ford Bronco Sport is the latest variant of Ford's troubled EcoBoost coolant intrusion problem. The open-deck block design allows coolant to leak internally into the cylinders, causing misfires, white exhaust smoke, and complete engine failure. Ford issued TSB 25-2063 in February 2025 addressing coolant loss in 2021-2024 Bronco Sport 1.5L models, recommending a coolant system flush to prevent recurrent water pump failures. Ford also extended warranty coverage to 7 years/84,000 miles for short block replacement due to coolant intrusion. BroncoSportForum.com documents numerous cases including owners stranded with brand-new vehicles. NHTSA opened an investigation into EcoBoost engine failures in October 2023 covering multiple Ford models.
Ford Crown Victoria(1 issue)
- 4.6L 2-Valve Spark Plug Ejection/Breakage1992-2011
The 4.6L 2-valve engine uses spark plugs that thread into aluminum heads with only a few threads of engagement. The plugs can eject from the head under load, stripping the threads. Later models (2004+) use a 2-piece plug design that can break during removal.
Ford Expedition(1 issue)
- 5.4L 2-Valve Spark Plug Blow-Out From Cylinder Head1997-2008
The 5.4L Triton 2-valve V8 in 1997-2008 Expeditions is notorious for spark plugs ejecting from the aluminum cylinder heads. The 2-valve heads have only 4 threads holding each spark plug, which is insufficient for the clamping force needed. Over time, the threads strip and the spark plug launches out of the head under combustion pressure, taking the ignition coil with it. This typically happens when spark plugs are removed and reinstalled, or spontaneously at high mileage.
Ford Freestar(1 issue)
- Ignition Coil Pack Failure2004-2007
The coil-on-plug ignition coils on the 3.9L and 4.2L V6 engines fail frequently, causing misfires, rough running, and reduced fuel economy. Often one coil fails and the others follow shortly.
Looking for P0306 on a different make?
View P0306 across all makes →Frequently Asked Questions
What does P0306 mean on Ford?▼
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 Ford specifically, this code is documented across 4 models.
What causes P0306 on Ford vehicles?▼
Common causes on Ford: 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). Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0306 on a Ford?▼
Repair costs on Ford range from $150 to $7,500, depending on the specific model and root cause.
Which Ford models have P0306 documented?▼
Au7o has documented P0306 on 4 Ford models: Bronco Sport, Crown Victoria, Expedition, Freestar.