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P0300

P0300 on a 2016 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 2016 Ford Focus Bev

Ranked from 1,137 NHTSA owner complaints filed for this vehicle.

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  1. 1

    Timing 'wet' belt-in-oil-sump disintegration clogging the oil pump pickup

    High severity

    The 1.0L EcoBoost's oil-pump drive belt, submerged in engine oil, is known to shed material that clogs the oil pump pickup tube; the resulting oil starvation causes rough running, stalling, and in several reported cases catastrophic engine failure — this is the subject of NHTSA Campaign 23V905000. Look for low oil pressure warnings, metallic debris in the oil pan, or an open engine/cooling recall.

    Reported in 12 NHTSA complaints
    Parts:timing belt (wet belt)oil pumpoil pump pickup tube
  2. 2

    Head gasket / internal coolant intrusion causing misfire with white exhaust smoke

    High severity

    Owners reported misfiring, heavy white smoke, and multiple stored codes consistent with coolant reaching a cylinder; confirm with a coolant loss with no external leak or a positive combustion-gas leak test in the coolant.

    Reported in 3 NHTSA complaints
    Parts:head gasket
  3. 3

    Worn or fouled spark plugs

    Medium severity

    Standard wear item; degraded gap or fouling on a small-displacement turbo engine readily produces a misfire.

    Common cause
    Parts:spark plugs
  4. 4

    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
  5. 5

    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
  6. 6

    Clogged or leaking fuel injector(s)

    Medium severity

    A dirty or dribbling injector on a direct/port-injected 3-cylinder disrupts the air/fuel balance; check injector flow and spray pattern.

    Common cause
    Parts:fuel injector
  7. 7

    Carbon-fouled intake valves

    Medium severity

    Direct-injection engines like this 1.0L EcoBoost are prone to intake-valve carbon buildup that disrupts airflow and causes misfire, especially at idle.

    Common cause
  8. 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

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

1

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.

2

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.

3

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.

4

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.

5

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 RoughFlashing Check Engine Light