P0300 on a 2015 Honda Accord 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 2015 Honda Accord Hybrid

Ranked from 609 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Internal engine damage (rod bearing failure, low compression)
High severity
Several owners describe a sudden knock or 'thunk', loss of power, and a mechanic-confirmed rod bearing or connecting-rod failure requiring engine replacement — a severe, vehicle-specific pattern that produces a hard multi-cylinder misfire before total failure.
Reported in 4 NHTSA complaints
2
Confirmed individual-cylinder misfire (P030x) from coil or fuel-delivery fault
Medium severity
One owner's scan tool specifically logged a P0304-type single-cylinder misfire alongside a limp-mode/traction-light event, confirming an active misfire condition on this vehicle.
Reported in 1 NHTSA complaint
Parts:ignition coil spark plugs
3
Vacuum leak from a deteriorated intake manifold gasket/plenum
Medium severity
An owner had the intake manifold plenum replaced after it corroded and broke down, explicitly causing vacuum leaks that upset the air/fuel mixture and idle quality.
Reported in 1 NHTSA complaint
Parts:intake manifold gasket
4
Carbon-fouled valves / plug fouling from oil consumption
Medium severity
One owner reports the engine burning roughly a quart of oil every 2,500-3,000 miles with a cold-start rattle; oil reaching the combustion chamber fouls plugs and coats valves, degrading combustion.
Reported in 1 NHTSA complaint
Parts:spark plugs
5
Worn spark plugs
Low severity
The single most common source of a random/multiple-cylinder misfire code across gasoline and hybrid engines alike; check gap and electrode wear at the recommended interval.
Common cause
Parts:spark plugs
6
Failing ignition coil(s)
Medium severity
A common misfire cause generally; also directly reflected in this batch by a case where a coil on one cylinder was replaced (unsuccessfully) before the real fault was traced further.
Common cause
Parts:ignition coil
7
Clogged or leaking fuel injectors
Medium severity
Deposits or a leaking injector can starve or over-fuel a cylinder, producing an intermittent misfire under load.
Common cause
Parts:fuel injector
8
EGR valve fault
Low severity
A stuck-open EGR valve dilutes the intake charge excessively at idle/low load and is a well-established contributor to rough idle and misfire codes.
Common cause
Parts:EGR valve

Part links go to Amazon search results for this vehicle. As an Amazon Associate, WrenchConnect earns from qualifying purchases — always confirm fitment for your exact trim and engine before ordering.

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.

Rather have a pro handle it? Find a vetted local mechanic.

Matching symptoms

Car Runs Rough Flashing Check Engine Light