P0300 on a 2019 Honda Odyssey

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 Honda Odyssey

Ranked from 894 NHTSA owner complaints filed for this vehicle.

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1
Connecting rod bearing wear/failure (NHTSA Recall 23V-751)
High severity
Multiple owners reported a knocking sound that progressed to confirmed connecting rod bearing failure, in several cases with the check-engine light flashing (active misfire) before the engine lost power or seized.
Reported in 8 NHTSA complaints
2
Failing fuel injector(s) — Honda TSB 21-010 / DTC P219A
High severity
Numerous owners had a dealer-confirmed failed fuel injector (DTC P219A, air-fuel ratio variation) tied to Honda Service Bulletin 21-010; Honda's own bulletin states defective injectors on this engine can cause misfires.
Reported in 4 NHTSA complaints
Parts:fuel injector
3
Worn spark plugs
Low severity
Standard wear item and the most common cause of a random misfire; check gap/condition against factory spec.
Common cause
Parts:spark plug
4
Failing ignition coil(s)
Medium severity
A weak coil-on-plug pack drops spark energy under load, producing a misfire on that cylinder.
Common cause
Parts:ignition coil
5
Vacuum/intake leak
Medium severity
Unmetered air leans out one or more cylinders enough to misfire, especially noticeable at idle.
Common cause
6
Carbon-fouled intake valves
Medium severity
Direct-injected V6 engines are prone to intake valve carbon buildup that disrupts airflow/atomization and can produce rough running.
Common cause
7
EGR valve fault
Low severity
A stuck-open EGR valve dilutes the intake charge excessively, especially at idle/low load, and can trigger a 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