P0300 on a 2020 Honda Ridgeline

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 2020 Honda Ridgeline

Ranked from 163 NHTSA owner complaints filed for this vehicle.

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1
Spun/worn connecting-rod bearings (documented on this 3.5L V6) causing low compression and rough running
High severity
Multiple 2020 Ridgeline owners had rod bearings spin/fail (cylinders #3/#5/#6) between 70k-140k miles with no warning lamp, producing engine knock and rough running that can register as a misfire before the engine needs replacement.
Reported in 5 NHTSA complaints
2
Critically low engine oil accelerating bottom-end wear/knock
High severity
One owner found the engine essentially out of oil after a knocking noise and stall, consistent with the same bottom-end wear pattern seen fleet-wide on this engine.
Reported in 1 NHTSA complaint
3
Worn spark plugs
Medium severity
Standard high-mileage wear item and the most common overall P0300 cause.
Common cause
Parts:spark plugs
4
Failing ignition coil(s)
Medium severity
A weak or intermittent coil produces a repeatable single- or multi-cylinder misfire.
Common cause
Parts:ignition coil
5
Clogged or leaking fuel injector
Medium severity
Uneven fuel delivery to one cylinder is a common, easily-tested misfire cause.
Common cause
Parts:fuel injector
6
Vacuum leak (intake gasket, hose)
Medium severity
Unmetered air entering the intake disrupts the air-fuel ratio enough to misfire, especially at idle.
Common cause
7
Carbon-fouled intake valves (direct injection)
Medium severity
Direct-injection engines build carbon on the intake valve backs over time, disrupting airflow and causing misfire.
Common cause
8
Faulty EGR valve
Low severity
A stuck EGR valve dilutes the intake charge unevenly, producing a rough-idle 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