P0300 on a 2021 Ford F 150 Super Cab 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 2021 Ford F 150 Super Cab Diesel

Ranked from 941 NHTSA owner complaints filed for this vehicle.

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1
Worn or cracked spark plugs
Medium severity
Two separate owners of this truck had misfires traced directly to spark plugs -- one to cracked plugs, another after replacing all six -- the single most common P0300 root cause.
Reported in 2 NHTSA complaints
Parts:spark plugs
2
Failing ignition coil(s)
Medium severity
One owner's misfire fix included replacing an ignition coil alongside the plugs; a coil that's breaking down under load drops spark energy on that cylinder.
Reported in 1 NHTSA complaint
Parts:ignition coil
3
Clogged or failing fuel injector(s)
Medium severity
One owner replaced all injectors (with coils and plugs) chasing a persistent idle/hot-fuel misfire, pointing to injector delivery as part of the pattern on this truck.
Reported in 1 NHTSA complaint
Parts:fuel injector
4
Low compression from valve or piston damage
High severity
An independent inspection on this exact truck found a damaged #4 piston top from a suspected valve failure, causing severe power loss consistent with a dead-cylinder misfire.
Reported in 1 NHTSA complaint
5
Timing chain/phaser fault (Coyote V8 known issue)
High severity
One owner's check-engine light with an abnormal rattle was flagged by the Ford app as a timing failure -- a known contributor to rough running/misfire on this V8.
Reported in 1 NHTSA complaint
6
Vacuum or intake air leak
Medium severity
Unmetered air leaning out one or more cylinders can present as a random misfire, especially at idle; check hoses, gaskets, and PCV lines with smoke.
Common cause
7
Carbon-fouled intake valves
Low severity
Direct-injection engines build carbon on the backs of the intake valves over time, disrupting airflow/fuel atomization enough to cause intermittent misfire.
Common cause
8
EGR system fault
Low severity
A stuck-open EGR valve dilutes the intake charge excessively, especially at idle and low load, producing a misfire pattern.
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