P0300 on a 2021 Honda Pilot

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 Honda Pilot

Ranked from 407 NHTSA owner complaints filed for this vehicle.

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1
Spun or worn connecting-rod/main bearing causing rod knock and engine failure (documented 3.5L V6 issue)
High severity
Multiple owners of this exact model report a knocking engine, metal shavings in the oil, and dealer-confirmed rod/crankshaft bearing failure requiring full engine replacement — a well-known 3.5L J-series bearing problem that produces a rough-running, misfiring engine before it fails outright.
Reported in 6 NHTSA complaints
2
Dealer-confirmed cylinder misfire on scan (e.g., "Cylinder 2 Misfire")
High severity
One complaint documents an actual dealer scan reading of a specific-cylinder misfire, and another describes a blinking/active check-engine light with the vehicle dropping into limp mode — both directly diagnostic of an active P0300-type misfire event.
Reported in 2 NHTSA complaints
3
Worn spark plugs
Medium severity
Worn electrodes or fouling widen the spark gap until the plug misfires under load; a routine and common cause on any gasoline V6.
Common cause
Parts:spark plugs
4
Failing ignition coil(s)
Medium severity
A cracked or weak coil-on-plug unit drops spark energy to one cylinder, often worse when hot or under load.
Common cause
Parts:ignition coil
5
Clogged or leaking fuel injector(s)
Medium severity
An injector that's partially clogged or dribbling unbalances that cylinder's air/fuel ratio enough to misfire.
Common cause
Parts:fuel injector
6
Vacuum leak
Medium severity
Unmetered air leaning out one or more cylinders can present as a misfire, especially noticeable at idle.
Common cause
Parts:vacuum hose
7
Carbon-fouled intake valves
Low severity
Direct-injection engines accumulate carbon on the backs of the intake valves, disrupting airflow enough to cause a misfire.
Common cause
8
EGR valve or passage fault
Low severity
A stuck-open EGR valve or clogged passage can dump excess exhaust gas into a cylinder at the wrong time, causing it to 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