P0300 on a 2017 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 2017 Ford Fusion Energi

Ranked from 1,030 NHTSA owner complaints filed for this vehicle.

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1
Coolant intrusion into the cylinders from a cracked cylinder head/head gasket
High severity
The large majority of complaints in this batch (dealer-diagnosed) describe coolant entering the cylinders -- white/sweet-smelling exhaust smoke, low coolant with no visible leak, and misfire/rough-run codes -- a well-documented issue on this engine.
Reported in 24 NHTSA complaints
Parts:cylinder head head gasket
2
Spark plugs fouled or worn from coolant/oil intrusion
Medium severity
Several complaints note spark plug replacement or plugs found wet with coolant as part of the misfire diagnosis.
Reported in 3 NHTSA complaints
Parts:spark plugs
3
Failing ignition coil
Medium severity
One complaint's misfire was diagnosed with a scan tool pointing at cylinder-specific ignition performance; swap-test or inspect coil packs on any misfiring cylinder.
Reported in 1 NHTSA complaint
Parts:ignition coil
4
Vacuum leaks
Medium severity
Unmetered air causes lean misfire, especially at idle; check intake boots, PCV lines, and brake booster hose with a smoke test.
Common cause
5
Clogged or leaking fuel injectors
Medium severity
A partially clogged or dribbling injector produces a lean or wet-fouled cylinder; check injector balance/flow rates.
Common cause
Parts:fuel injector
6
Low compression from rings/valves worn or washed down by coolant intrusion
High severity
Coolant washing the cylinder walls strips lubrication and can score the bore, dropping compression on the affected cylinder(s); confirm with a compression or leak-down test.
Common cause
7
Carbon-fouled valves
Low severity
Direct-injection engines are prone to intake valve carbon buildup that disrupts airflow/combustion on affected cylinders; inspect with a borescope.
Common cause
8
EGR faults
Low severity
A stuck-open EGR valve dilutes the intake charge and can cause a rough idle/misfire; check EGR flow and valve operation.
Common cause

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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