P0300 on a 2017 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 2017 Ford Focus Bev

Ranked from 842 NHTSA owner complaints filed for this vehicle.

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1
Timing belt tooth shear (belt-in-oil design)
High severity
One owner's vehicle stalled and lost power on the highway; the dealer found the timing belt had sheared teeth that were circulating in the oil, which knocks valve timing out and produces a severe multi-cylinder misfire on this engine's belt-in-oil design.
Reported in 1 NHTSA complaint
Parts:timing belt kit timing belt tensioner
2
Low compression from cylinder/head gasket damage
High severity
One owner's engine needed a long-block, turbo, and catalytic converter replacement after a head-gasket failure cracked cylinder 3 — mechanical damage of that kind will produce persistent misfire codes.
Reported in 1 NHTSA complaint
3
Worn or fouled spark plugs
Medium severity
Excessive gap or fouling weakens spark and is the most common misfire cause.
Common cause
Parts:spark plugs
4
Failing ignition coil(s)
Medium severity
A breaking-down coil drops spark energy, often worse under load or heat soak.
Common cause
Parts:ignition coil
5
Clogged or leaking fuel injector(s)
Medium severity
A partially clogged or dribbling injector disrupts the mixture on that cylinder.
Common cause
Parts:fuel injector
6
Vacuum leak
Medium severity
Unmetered air entering through a cracked hose or gasket leans out one or more cylinders enough to misfire.
Common cause
7
Carbon-fouled intake valves
Medium severity
Direct-injection engines are prone to carbon buildup on the backs of the intake valves.
Common cause
8
EGR valve fault
Low severity
A stuck-open EGR valve dumps excess exhaust into the intake at idle, causing a rough-running 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