P0300 on a 2020 Ford F 150 Supercab Diesel

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 2020 Ford F 150 Supercab Diesel

Ranked from 506 NHTSA owner complaints filed for this vehicle.

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1
Cam phaser (VCT) failure
High severity
Multiple owners report a cold-start rattle/tick followed by rough idle traced to failed cam phasers -- a well-documented issue on this 5.0L covered by Ford campaigns 21B10/21N03; the resulting valve timing error causes rough running and misfire-like symptoms.
Reported in 8 NHTSA complaints
Parts:cam phaser timing chain
2
Low compression from excessive oil consumption/worn engine internals
High severity
Numerous complaints describe heavy oil consumption (up to 2 qts/1300 mi) and eventual engine replacement on this generation 5.0L; worn rings/cylinders lower compression enough to cause a rough-running misfire.
Reported in 7 NHTSA complaints
Parts:piston rings
3
Worn or fouled spark plugs
Low severity
Plugs worn past gap spec or fouled with carbon/oil misfire under load; check spark plug condition and gap against spec.
Common cause
Parts:spark plugs
4
Failing ignition coil(s)
Medium severity
A weak or dying coil produces an intermittent, cylinder-specific misfire, often worse when hot or under load; swap coils cylinder-to-cylinder to confirm.
Common cause
Parts:ignition coil
5
Vacuum/intake leak
Medium severity
Unmetered air entering after the MAF causes a lean misfire, most noticeable at idle; check intake boots, PCV lines, and manifold gaskets.
Common cause
6
Clogged or leaking fuel injector(s)
Medium severity
A partially clogged or dribbling injector delivers uneven fuel to a cylinder, producing a persistent misfire on that cylinder.
Common cause
Parts:fuel injector
7
Carbon-fouled intake valves
Low severity
Direct-injection engines build up carbon on the backs of intake valves over time, disrupting airflow/fuel atomization and causing misfire.
Common cause
8
EGR valve fault
Low severity
A stuck-open EGR valve dilutes the intake charge excessively at idle/low load, causing a rough idle and misfire code.
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