P0300 on a 2019 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 2019 Ford Fusion
Ranked from 369 NHTSA owner complaints filed for this vehicle.
- 1
Coolant Intrusion into Cylinders (Engine Block/Head Gasket Defect)
High severityCoolant leaks internally into the combustion chambers due to a known engine block/head gasket design flaw, causing misfires, rough running, and white smoke. Confirmed by low coolant without external leaks, pressure testing, and borescope inspection showing coolant in cylinders.
Reported in 22 NHTSA complaints - 2
Faulty Ignition Coils
Medium severityA failing ignition coil cannot provide enough spark to ignite the air/fuel mixture, leading to a misfire. Confirmed by swapping the coil to another cylinder and seeing if the misfire follows.
Common cause - 3
Worn or Fouled Spark Plugs
Low severitySpark plugs wear out over time or become fouled by carbon, oil, or coolant, preventing proper ignition. Confirmed by visual inspection of the spark plug electrodes.
Common cause - 4
Vacuum Leak
Medium severityUnmetered air enters the intake manifold, causing a lean condition that results in random misfires. Confirmed by a smoke test or listening for hissing noises around intake hoses.
Common cause - 5
Faulty Fuel Injectors
Medium severityClogged or failing fuel injectors fail to deliver the correct amount of fuel, causing a lean misfire. Confirmed by checking injector resistance, listening for clicking, or performing a fuel pressure drop test.
Common cause - 6
Low Fuel Pressure
Medium severityA failing fuel pump or clogged fuel filter restricts fuel delivery, causing multiple cylinders to misfire under load. Confirmed by attaching a mechanical fuel pressure gauge to the fuel rail.
Common cause
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.
Rather have a pro handle it? Find a vetted local mechanic.