P0300 on a 2018 Ford Expedition

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 2018 Ford Expedition

Ranked from 363 NHTSA owner complaints filed for this vehicle.

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1
Cam phaser / VVT timing chain wear (3.5L EcoBoost)
High severity
This engine has a well-documented pattern of cam phaser and timing-chain wear (subject of recalls/CSP 21N03 and 24E13) that throws valve timing off and produces rough running, hesitation, and misfire; look for a cold-start rattle plus timing-related fault codes.
Reported in 13 NHTSA complaints
Parts:camshaft phaser timing chain kit
2
Low compression from internal engine wear (worn rings/valves)
High severity
A confirmed cylinder-specific misfire with measured low compression indicates worn rings, valves, or a related internal fault rather than an ignition-system part.
Reported in 1 NHTSA complaint
3
Worn spark plugs
Low severity
Aged or fouled plugs misfire under load; check gap/wear and replace on the recommended interval.
Common cause
Parts:spark plugs
4
Failing ignition coil(s)
Medium severity
A cracked or weak coil-on-plug misfires a specific cylinder, especially under boost; swap coils cylinder-to-cylinder to confirm.
Common cause
Parts:ignition coil
5
Clogged or leaking fuel injector
Medium severity
A dirty or leaking injector causes an uneven air/fuel mixture on one cylinder; check injector balance/spray pattern.
Common cause
Parts:fuel injector
6
Vacuum/intake leak
Medium severity
Unmetered air entering after the MAF sensor leans out a cylinder or bank enough to misfire; check intake boots and manifold gaskets with a smoke test.
Common cause
7
Carbon-fouled valves
Low severity
Direct-injection engines like this EcoBoost build carbon on intake valves over time, disrupting airflow and causing misfire; visible with a borescope.
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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Matching symptoms

Car Runs Rough Flashing Check Engine Light