P0300 on a 2016 Ford Fusion Energi

P0300 is a generic OBD2 powertrain code for random or multiple cylinder misfire. Unlike P0301 through P0308, it does not point to one specific cylinder, so the cause can be ignition, fuel, air, sensor, or mechanical.

Not your vehicle? See general P0300 info.

Most common causes on the 2016 Ford Fusion Energi

Ranked from 1,455 NHTSA owner complaints filed for this vehicle.

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1
Coolant intrusion into the cylinder(s) from a cracked engine block / head gasket (EcoBoost open-deck design flaw)
High severity
By far the dominant pattern in this batch: coolant leaks into a cylinder with no external puddle, fouling that cylinder and setting a misfire (often P0301-P0304) that snowballs into P0300; Ford TSB 19-2346 documents this exact failure on the 1.5L/2.0L EcoBoost and generally requires a long-block replacement.
Reported in 25 NHTSA complaints
2
Failing ignition coil(s)
Medium severity
One owner's independent mechanic replaced the coil-on-plug solenoid/coils before the coolant intrusion was correctly diagnosed as the real cause -- worth ruling out first since it's the cheaper part.
Reported in 1 NHTSA complaint
Parts:ignition coil
3
Worn or fouled spark plugs
Low severity
Standard high-mileage misfire cause; a plug soaked in oil or coolant from the intrusion above will also read as fouled.
Common cause
Parts:spark plug
4
Vacuum or intake air leak
Medium severity
Unmetered air entering after the MAF sensor leans out one or more cylinders enough to misfire under load.
Common cause
5
Low cylinder compression from worn rings or valves
High severity
Coolant or oil washing the cylinder walls over time accelerates ring/valve wear, permanently lowering compression in that cylinder.
Common cause
6
Clogged or leaking fuel injector
Medium severity
A partially clogged or dribbling injector under- or over-fuels a single cylinder, producing a steady misfire on that cylinder.
Common cause
Parts:fuel injector
7
EGR valve fault
Low severity
A stuck-open EGR valve can dilute the intake charge enough to cause a rough idle/misfire, especially at low RPM.
Common cause
Parts:EGR valve

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These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0300 on your car still needs shop confirmation before any repair.

Common symptoms

Flashing or steady check engine light
Rough idle
Shaking under acceleration
Loss of power
Fuel smell from exhaust

What to check before replacing parts

Scan for cylinder-specific misfire codes

Look for: A companion P0301–P0308 pins the misfire to one cylinder — start there. P0300 with no cylinder code points at something hitting several at once: fuel pressure, a large vacuum leak, or timing.

Inspect the spark plugs and coils

Look for: Pull the plugs: black/sooty = rich, oily = oil intrusion, white/blistered = lean or overheating, cracked porcelain or an out-of-spec gap = replace. Then swap a coil to another cylinder — if a cylinder-specific code follows the coil, the coil is bad.

Check fuel trims for a vacuum leak

Look for: High positive short- and long-term trims (worst at idle, improving as RPM rises) mean unmetered air is getting in. Smoke-test the intake and listen for hissing.

Verify fuel pressure

Look for: Compare running/cranking pressure to the vehicle spec. Low or dropping pressure starves multiple cylinders and reads as a random misfire — suspect the pump, filter, or regulator.

Compression / leak-down test if ignition and fuel check out

Look for: A cylinder 15%+ below the others, or leak-down hissing from the intake (intake valve), exhaust (exhaust valve), or oil filler (rings), means the misfire is mechanical — not a swap-in part.

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Matching symptoms

Car Runs Rough Flashing Check Engine Light