P0300 on a 2021 Honda Cr V Hybrid

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 Cr V Hybrid

Ranked from 410 NHTSA owner complaints filed for this vehicle.

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1
Head gasket failure allowing coolant into a cylinder, fouling plugs (NHTSA PE25016 / Bissell v. American Honda)
High severity
Multiple dealer-confirmed head gasket failures let coolant leak directly onto/into the cylinder and spark plugs on this exact engine, a documented factory defect that reliably produces a misfire.
Reported in 7 NHTSA complaints
Parts:head gasket spark plugs
2
Failed or clogged fuel injector(s)
Medium severity
Several owners had a fuel injector diagnosed and replaced (sometimes the full injector kit) as the cause of stalling/misfire events on this vehicle.
Reported in 4 NHTSA complaints
Parts:fuel injector
3
Worn or fouled spark plugs
Medium severity
Dealers repeatedly pulled and replaced spark plugs (found discolored/fouled) in response to flashing check-engine and misfire events on this model.
Reported in 3 NHTSA complaints
Parts:spark plugs
4
Carbon buildup on intake valves/injectors (direct-injection engine)
Medium severity
Owners and mechanics point to carbon buildup and 'sludge' as a contributor to rough running and misfire on this direct-injection engine.
Reported in 2 NHTSA complaints
5
Failing ignition coil(s)
Medium severity
A coil losing spark under load or heat is a classic misfire cause; one owner swapped coils and plugs while troubleshooting a persistent cylinder-1 misfire.
Common cause
Parts:ignition coil
6
Vacuum/intake air leak
Low severity
Unmetered air entering after the throttle body leans out one or more cylinders enough to misfire, especially at idle.
Common cause
7
Low compression from worn piston rings/valves
High severity
Chronic oil dilution and coolant intrusion on this engine can accelerate ring and valve wear, producing a persistent low-compression misfire.
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