P0300 on a 2015 Honda Accord

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 2015 Honda Accord

Ranked from 594 NHTSA owner complaints filed for this vehicle.

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1
Internal Engine Failure (Rod Bearing / Cylinder Damage)
High severity
Severe internal damage, such as a spun rod bearing or loss of compression in cylinders, can cause misfires and engine knocking. A compression test, leak down test, or finding metal shavings in the oil confirms this.
Reported in 3 NHTSA complaints
2
Fuel Pump Failure
High severity
A failing fuel pump can cause low fuel pressure, leading to lean conditions and random misfires. A fuel pressure test will confirm if the pump is delivering the correct pressure.
Reported in 1 NHTSA complaint
3
Vacuum Leaks / Intake Manifold Plenum Deterioration
Medium severity
Unmetered air entering the engine alters the air/fuel ratio, causing misfires. A smoke test or inspecting the intake manifold plenum for deterioration confirms the leak.
Reported in 1 NHTSA complaint
4
Faulty Spark Plugs
Low severity
Worn or fouled spark plugs are a leading cause of misfires. Inspection of the spark plug electrodes will show wear, carbon buildup, or incorrect gap.
Common cause
5
Defective Ignition Coils
Medium severity
A failing ignition coil will not provide sufficient voltage to the spark plug, causing a misfire. Swapping the coil to another cylinder and seeing if the misfire follows confirms this.
Common cause
6
Clogged or Faulty Fuel Injectors
Medium severity
Injectors that are clogged or failing electrically will not deliver the proper amount of fuel, causing a misfire. Injector balance testing or checking resistance confirms the issue.
Common cause

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