P0300 on a 2019 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 2019 Ford F 150 Supercab Diesel
Ranked from 953 NHTSA owner complaints filed for this vehicle.
- 1
Failing cam phasers (VVT actuator locking-pin failure)
High severityA very large share of owners on this exact 3.5L EcoBoost report the well-documented cold-start rattle/knock from failed cam phasers (Ford TSB 19-2208/19-2365, CSP 21N03/21B10), which throws valve timing off enough to cause rough idle and misfire-type symptoms.
Reported in 10 NHTSA complaints - 2
Excessive oil consumption from internal engine wear
High severityMultiple owners had confirmed oil-consumption tests (roughly a quart per 1,000 miles) with no external leak, indicating internal wear that also contributes to low compression and rough running.
Reported in 2 NHTSA complaints - 3
Timing chain stretch/wear
High severityOne owner's engine lost power under load and the dealer traced it to the timing chain, which was replaced along with related components.
Reported in 1 NHTSA complaint - 4
Worn spark plugs
Low severityA standard misfire check; one owner had plugs replaced when the engine sputtered/vibrated at idle (though the underlying rattle persisted).
Reported in 1 NHTSA complaintParts:spark plug - 5
Vacuum or intake air leak
Medium severityUnmetered air disrupts the air-fuel mixture enough to cause an intermittent misfire.
Common cause - 6
Clogged or leaking fuel injectors
Medium severityReduced or uneven fuel delivery to a cylinder is a classic single/random misfire cause.
Common causeParts:fuel injector - 7
Carbon-fouled intake valves
Medium severityDirect-injection EcoBoost engines are prone to carbon buildup on the valves since fuel never washes them, which can disrupt sealing/airflow enough to misfire.
Common cause - 8
Low compression from worn rings/valves
High severityMechanical wear reduces a cylinder's ability to build compression, producing a persistent misfire on that cylinder.
Common cause
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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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