P0300 on a 2017 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 2017 Honda Accord
Ranked from 527 NHTSA owner complaints filed for this vehicle.
- 1
Faulty Fuel Injectors / Clogged Fuel Injectors
High severityFuel injector failure or clogging causes misfires, hesitation, and stalling. Look for P0300/P0302 codes, loss of power, and jerking during acceleration.
Reported in 5 NHTSA complaints - 2
Failing Fuel Pump
High severityA failing fuel pump starves the engine of fuel, leading to stalling, hesitation, and misfires. Confirm by checking fuel pressure and looking for stalling at stops or while driving.
Reported in 5 NHTSA complaints - 3
Piston Ring Failure / Excessive Oil Consumption
High severityWorn piston rings allow oil into the combustion chamber, fouling spark plugs and causing misfires. Check for low oil levels and fouled spark plugs.
Reported in 3 NHTSA complaints - 4
Faulty Spark Plugs / Fouled Spark Plugs
Medium severityWorn or oil-fouled spark plugs fail to ignite the air-fuel mixture, causing misfires. Inspect spark plugs for excessive wear, carbon buildup, or oil fouling.
Reported in 2 NHTSA complaints - 5
Faulty Ignition Coil
Medium severityA failing ignition coil cannot provide sufficient voltage to the spark plug, resulting in a misfire. Swap coils between cylinders to see if the misfire moves.
Reported in 1 NHTSA complaint - 6
Broken Valve Spring / Bent Valve
High severityInternal engine failure such as a broken valve spring prevents proper valve operation, causing severe misfires and loss of compression. Requires internal engine inspection.
Reported in 1 NHTSA complaint - 7
Loose Timing Chain / Cam Chain Tensioner Failure
High severityA loose timing chain alters valve timing, leading to misfires and potential internal engine damage. Listen for rattling noises on startup and check timing marks.
Reported in 1 NHTSA complaint - 8
Valve Clearance Out of Adjustment
Medium severityImproper valve clearance can cause poor sealing and misfires, especially when cold. A valve adjustment may be required if clearance is out of spec.
Reported in 1 NHTSA complaint - 9
Vacuum Leak
Medium severityUnmetered air entering the intake manifold leans out the air-fuel mixture, causing random misfires. Check for cracked hoses or intake manifold gasket leaks.
Common cause - 10
Low Fuel Pressure
Medium severityInsufficient fuel pressure prevents proper atomization of fuel, leading to lean misfires. Verify fuel pressure with a mechanical gauge.
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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