P0300 on a 2018 Ford Focus Bev

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 2018 Ford Focus Bev

Ranked from 743 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Head gasket failure allowing coolant into the combustion chamber (NHTSA Campaign 23V905000)
High severity
This complaint set is dominated by an open Ford engine recall; multiple owners report a diagnosed head-gasket failure or coolant intrusion into the cylinders causing engine damage, one explicitly describes the engine 'misfiring significantly,' and another describes the check-engine light blinking (the classic active-misfire warning) right before the engine lost power and caught fire.
Reported in 5 NHTSA complaints
2
Oil pump drive belt failure causing oil starvation (Recall 23S64/23V905)
High severity
Several owners report the oil pump drive belt failing, cutting oil pressure and causing engine damage; a starving, damaged engine will run roughly and misfire before it seizes.
Reported in 2 NHTSA complaints
3
Worn or fouled spark plugs
Low severity
The baseline general misfire cause; inspect gap and condition, especially if plugs are overdue for replacement.
Common cause
Parts:spark plugs
4
Failing ignition coil(s)
Medium severity
A weak coil produces a repeatable single-cylinder misfire; verify by swapping coils between cylinders.
Common cause
Parts:ignition coil
5
Clogged or leaking fuel injector(s)
Medium severity
A restricted or dribbling injector starves or floods a cylinder, producing a repeatable misfire on that cylinder.
Common cause
Parts:fuel injector
6
Vacuum/intake air leak
Medium severity
Unmetered air causes a lean misfire, typically worse at idle; smoke-test intake gaskets and hoses.
Common cause
7
Low cylinder compression (worn rings/valves)
High severity
Poor ring or valve sealing on a high-mileage or oil-starved engine reduces cylinder pressure enough to misfire under load.
Common cause

Part links go to Amazon search results for this vehicle. As an Amazon Associate, WrenchConnect earns from qualifying purchases — always confirm fitment for your exact trim and engine before ordering.

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.

Matching symptoms

Car Runs Rough Flashing Check Engine Light