P0300 on a 2023 Honda Civic Sedan

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 2023 Honda Civic Sedan

Ranked from 251 NHTSA owner complaints filed for this vehicle.

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1
Head gasket failure allowing coolant into a cylinder
High severity
Coolant entering a combustion chamber reliably produces a persistent multi-cylinder misfire; one owner reported premature head gasket failure at 75,000 miles on this exact model.
Reported in 1 NHTSA complaint
Parts:head gasket
2
Rodent damage to the engine wiring harness disrupting ignition or injector circuits
Medium severity
One owner reported rodents chewing through vehicle wiring twice within a week, compromising acceleration and emissions-related systems; damaged ignition or injector wiring can produce exactly this kind of misfire.
Reported in 1 NHTSA complaint
Parts:wiring harness
3
Wiring or sensor fault causing rough running shortly after purchase
Medium severity
One owner of a nearly-new example (about 1,000 miles) reported the engine running rough with the check-engine light and several other system alerts on simultaneously, suggesting an early production wiring or sensor defect.
Reported in 1 NHTSA complaint
4
Worn spark plugs
Medium severity
The most universally common cause of a random/multiple misfire code across manufacturers.
Common cause
Parts:spark plugs
5
Failing ignition coil(s)
Medium severity
A weakening coil can misfire intermittently, often worse under load, cold start, or when hot.
Common cause
Parts:ignition coil
6
Clogged or failing fuel injector(s)
Medium severity
A partially blocked or electrically weak injector starves a cylinder of fuel, producing a misfire.
Common cause
Parts:fuel injector
7
Vacuum or intake leak
Medium severity
Unmetered air entering downstream of the MAF sensor leans out one or more cylinders enough to misfire.
Common cause
Parts:intake gasket
8
Low compression from carbon-fouled valves or worn piston rings
High severity
Mechanical wear that reduces a cylinder's ability to seal produces a chronic, hard-to-clear 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