P0300 on a 2019 Honda Civic Hatch

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 Civic Hatch

Ranked from 414 NHTSA owner complaints filed for this vehicle.

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1
Head gasket failure allowing coolant intrusion into a cylinder
High severity
This engine family has a documented head-gasket weak point; several owners report sudden misfire/power loss, cylinders flooded with coolant, or a mechanic-confirmed blown head gasket that fouls plugs and destroys the engine.
Reported in 4 NHTSA complaints
Parts:head gasket
2
Ignition coil / spark plug corrosion from water intrusion (hood-scoop design issue)
Medium severity
Owners of this generation report water entering through the hood scoop and dripping onto cylinder 4, rusting the coil and plug and triggering the check-engine light — a direct misfire source.
Reported in 2 NHTSA complaints
Parts:ignition coil spark plug
3
Failing ignition coil(s)
Medium severity
One owner had coil packs and plugs replaced after a jerk/shudder with the check-engine light on, indicating the coils were suspected as the misfire source.
Reported in 1 NHTSA complaint
Parts:ignition coil
4
Worn or fouled spark plugs
Low severity
Widened gaps or fouling reduce spark energy and are among the most common misfire triggers; inspect gap, wear, and deposits.
Common cause
Parts:spark plug
5
Clogged or leaking fuel injector
Medium severity
A restricted or dripping injector causes an uneven air-fuel mixture on that cylinder; check injector balance/spray pattern.
Common cause
Parts:fuel injector
6
Vacuum leak (intake or PCV hose)
Medium severity
Unmetered air leans out one or more cylinders enough to misfire, especially at idle; smoke-test the intake tract and PCV lines.
Common cause
7
Carbon-fouled intake valves
Medium severity
Direct-injection engines like this 1.5T lack port fuel washing the valves, letting carbon build up and disrupt airflow/sealing enough to misfire; inspect with a borescope.
Common cause
8
Low compression from worn piston rings or valves
High severity
Mechanical wear reduces cylinder sealing enough to misfire under load; confirm with a compression or leak-down test.
Common cause
9
EGR valve or passage fault
Low severity
A stuck-open EGR valve or clogged passage disrupts combustion, especially at idle/cruise; test EGR flow and inspect for carbon blockage.
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