P0300 on a 2015 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 2015 Ford Fusion Energi
Ranked from 995 NHTSA owner complaints filed for this vehicle.
- 1
Coolant intrusion into cylinders (1.5L EcoBoost cracked head/block casting)
High severityThis is by far the dominant, well-documented pattern in this vehicle's complaints: internal coolant leakage into one or more cylinders (Ford TSB 19-2208/20-2100) fouls combustion and repeatedly triggers cylinder misfire codes (P0302/P0303/P0316 reported directly), often ending in engine or short-block replacement.
Reported in 18 NHTSA complaints - 2
Spark plugs fouled by coolant intrusion
Medium severityOne complaint on a coolant-intrusion vehicle notes rough starting consistent with coolant-fouled plugs; plugs exposed to coolant vapor foul quickly and misfire.
Reported in 1 NHTSA complaintParts:spark plug - 3
Failing ignition coil(s)
Medium severityA weak or arcing coil produces a cylinder-specific misfire independent of the coolant-intrusion issue; swap-test coils between cylinders to confirm.
Common causeParts:ignition coil - 4
Clogged or leaking fuel injector
Medium severityA restricted or dribbling injector starves or over-fuels a cylinder; an injector balance test isolates the cylinder.
Common causeParts:fuel injector - 5
Vacuum or intake leak
Low severityUnmetered air entering downstream of the turbo/throttle leans out a cylinder enough to misfire on this small-displacement turbo engine.
Common cause - 6
EGR fault
Low severityA stuck or leaking EGR valve upsets the air/fuel charge enough to produce a misfire, especially at idle.
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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