P0300 on a 2021 Ford Explorer

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 2021 Ford Explorer

Ranked from 402 NHTSA owner complaints filed for this vehicle.

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1
3.0L EcoBoost intake valve/valve-spring and bearing failure (NHTSA recalls 24V598000 & 24V635000)
High severity
A large cluster of owners on this 3.0L EcoBoost engine report knocking, fractured intake valves/timing chain, spun/failed bearings, and lost cylinder compression, several tied directly to the two open engine recalls -- mechanical damage of exactly this kind causes multi-cylinder misfire.
Reported in 12 NHTSA complaints
2
Cracked/fractured catalytic converter (multi-piece welded design, Ford Campaign 21E11)
High severity
One owner's scan directly returned a catalytic-converter code together with misfires across numerous cylinders, and two other owners had a dealer confirm the converter had fractured at its welds; a broken-up converter can restrict exhaust flow and induce misfire.
Reported in 3 NHTSA complaints
Parts:catalytic converter
3
Coolant intrusion into engine oil from a failing water pump
High severity
Two owners had a dealer diagnose antifreeze mixed into the engine oil from an internal water-pump leak, damaging bearings/lubrication and producing rough-running/loss-of-power symptoms.
Reported in 2 NHTSA complaints
Parts:water pump
4
Worn spark plugs or failing ignition coil/wiring
Medium severity
One owner's dealer specifically replaced 'plugs and a wire' to address a multi-cylinder misfire, matching this platform's known coil/plug wear pattern.
Reported in 1 NHTSA complaint
Parts:spark plugs ignition coil
5
Turbocharger failure allowing oil into the intake
Medium severity
One owner had a blown turbo diagnosed after visible gray exhaust smoke and a sudden inability to accelerate; oil ingestion from a failed turbo seal fouls cylinders and can trigger misfire.
Reported in 1 NHTSA complaint
Parts:turbocharger
6
Vacuum leak
Medium severity
Unmetered air leaning out one or more cylinders can produce a random misfire pattern, especially at idle.
Common cause
7
Clogged or leaking fuel injector
Medium severity
Under- or over-fueling a single cylinder is a standard cause of a random/multiple misfire code.
Common cause
Parts:fuel injector
8
EGR valve fault
Low severity
A stuck-open EGR valve over-dilutes the intake charge at idle/light load, which can present as random 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