P0300 on a 2016 Ford Fusion

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

Ranked from 1,659 NHTSA owner complaints filed for this vehicle.

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1
Coolant intrusion into cylinders (cracked cylinder head/block on 1.5L/2.0L EcoBoost)
High severity
A large share of these owners describe coolant leaking directly into a cylinder (often #2 or #4), 'No Coolant' warnings, white exhaust smoke, and head-gasket/engine replacements diagnosed as coolant intrusion -- a well-documented design flaw on this engine family that fouls plugs and drowns combustion, triggering random/multi-cylinder misfire.
Reported in 17 NHTSA complaints
2
Low compression from internal engine damage (worn rings/pistons)
High severity
Metal shavings found in cylinders #1/#4 with oil on the pistons in #2/#3, and a separate piston fracture allowing oil into the spark plug chamber, both point to internal wear/damage that kills compression in specific cylinders.
Reported in 2 NHTSA complaints
3
Worn or fouled spark plugs
Medium severity
One owner's independent mechanic diagnosed a misfire-related shutdown as needing spark plug replacement.
Reported in 1 NHTSA complaint
Parts:spark plugs
4
Vacuum/intake air leak, including a stuck-open EVAP purge valve
Medium severity
One owner reported a purge valve causing rough idle and stalling in traffic, consistent with unmetered air upsetting idle fueling enough to trigger a misfire.
Reported in 1 NHTSA complaint
Parts:purge valve
5
Failing ignition coil(s)
Medium severity
A weak or arcing coil misfires under load; check for stored coil-specific misfire codes (P0301-P0306) alongside P0300.
Common cause
Parts:ignition coil
6
Clogged or leaking fuel injector
Medium severity
An injector delivering too little or too much fuel to one cylinder produces a repeatable misfire on that cylinder.
Common cause
Parts:fuel injector
7
Carbon-fouled intake valves
Low severity
Direct-injection engines like this EcoBoost are prone to carbon buildup on intake valves, disrupting airflow/combustion at idle and light load.
Common cause
8
EGR valve stuck open
Low severity
An EGR valve that doesn't fully close introduces excess exhaust gas at idle, diluting the intake charge enough to cause a misfire.
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