P0300 on a 2017 Ford Focus

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

Ranked from 892 NHTSA owner complaints filed for this vehicle.

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1
Timing 'wet' belt-in-oil-sump disintegration clogging the oil pump pickup
High severity
The EcoBoost's oil-pump drive belt is submerged in oil and known to shed material that clogs the oil pickup, causing oil starvation, rough running/stalling, and in reported cases seized engines — covered by NHTSA Campaign 23V905000. Look for low oil pressure warnings or metallic debris in the oil.
Reported in 6 NHTSA complaints
Parts:timing belt (wet belt)oil pump oil pump pickup tube
2
Cracked cylinder head / head gasket coolant intrusion (2.0L EcoBoost)
High severity
Owners report a known issue where the 2.0L EcoBoost's aluminum cylinder head cracks between the combustion chamber and coolant passages, or the head gasket fails, letting coolant enter a cylinder and cause misfire and internal engine damage; look for coolant loss with no external leak, white smoke, or a positive combustion-leak test in the coolant.
Reported in 3 NHTSA complaints
Parts:cylinder head cylinder head gasket
3
Failing canister purge valve (CPV) causing stall/lean misfire
Medium severity
Owners report the CPV failing and causing repeated stalling, with symptoms worsening at lower fuel levels; a leaking or stuck purge valve upsets the air/fuel mixture and can present as a misfire.
Reported in 2 NHTSA complaints
Parts:purge valve
4
Worn or fouled spark plugs
Medium severity
Standard wear item; degraded gap or fouling readily produces a misfire on this turbocharged 4-cylinder.
Common cause
Parts:spark plugs
5
Failing ignition coil(s)
Medium severity
A weak or intermittent coil produces a cylinder-specific misfire; swap-test coils between cylinders to confirm.
Common cause
Parts:ignition coil
6
Vacuum or intake leak
Medium severity
Unmetered air past the MAF causes a lean misfire, particularly at idle; smoke-test intake boots and PCV hose.
Common cause
7
Carbon-fouled intake valves
Medium severity
Direct-injection EcoBoost engines are prone to intake-valve carbon buildup that disrupts airflow and can cause misfire, especially at idle.
Common cause
8
EGR valve or passage fault
Low severity
A stuck or clogged EGR disrupts combustion at idle/light load, contributing to an intermittent 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