P0300 on a 2021 Honda Cr V
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
Ranked from 311 NHTSA owner complaints filed for this vehicle.
- 1
Head gasket failure allowing coolant intrusion into the cylinder (documented CR-V/CR-V Hybrid 1.5T defect, NHTSA PE25016)
High severityMany owners of this exact vehicle report a diagnosed blown/failed head gasket letting coolant reach the spark plugs or a cylinder, producing a cold-start misfire and white exhaust smoke; this is under active NHTSA investigation and class-action litigation for this model.
Reported in 7 NHTSA complaints - 2
Failing or carbon-fouled fuel injectors
High severityRepeated dealer replacements of fuel injectors on this exact vehicle for flashing-check-engine misfire events point to injector failure/carbon buildup as a major misfire source.
Reported in 6 NHTSA complaintsParts:fuel injector - 3
Worn or fouled spark plugs
Medium severitySeveral owners had spark plugs replaced (sometimes repeatedly) as part of chasing misfire codes, often fouled by oil or coolant contamination.
Reported in 3 NHTSA complaintsParts:spark plug - 4
Failing high-pressure fuel pump
Medium severityOne owner's misfire/stall event traced to a P0087 low fuel-pressure code and a failed high-pressure fuel pump, a known weak point on this engine.
Reported in 1 NHTSA complaintParts:fuel pump - 5
Carbon buildup on intake valves (direct-injection engine)
Medium severityThis 1.5T direct-injection engine has no fuel washing the intake valves, so carbon deposits build up and disrupt airflow/sealing enough to cause a cold-start misfire.
Reported in 1 NHTSA complaint - 6
Vacuum or intake air leak
Medium severityUnmetered air entering one cylinder's intake runner produces a lean misfire localized to that cylinder.
Common cause - 7
EGR valve fault
Low severityA stuck-open EGR valve dilutes the intake charge and can trigger a misfire at idle or cold start.
Common causeParts: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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