P0300 on a 2016 Honda Civic
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 2016 Honda Civic
Ranked from 1,061 NHTSA owner complaints filed for this vehicle.
- 1
Head Gasket Failure / Coolant Leak into Cylinders
High severityCoolant loss with no external leaks, overheating, and misfires (P0300) due to coolant entering the combustion chamber. Confirmed by pressure testing the cooling system and inspecting cylinders for coolant.
Reported in 4 NHTSA complaints - 2
Faulty Spark Plugs / Ignition Coils
Medium severityWorn or fouled spark plugs and failing ignition coils prevent proper fuel ignition, leading to misfires. Confirmed by inspecting spark plugs for wear or rust and testing coil resistance.
Reported in 1 NHTSA complaint - 3
Low Cylinder Compression / Internal Engine Damage
High severityLoss of compression in cylinders (specifically noted as cylinders 2 and 3) prevents proper combustion, causing misfires. Confirmed by performing a cylinder compression test and leak-down test.
Reported in 1 NHTSA complaint - 4
Fuel Injector Failure
Medium severityClogged or failing fuel injectors disrupt the air-fuel mixture, causing random misfires. Confirmed by checking fuel trims, injector resistance, and performing an injector balance test.
Common cause - 5
Vacuum Leak / Intake Manifold Gasket Leak
Medium severityUnmetered air entering the intake manifold leans out the air-fuel mixture, leading to random misfires. Confirmed by a smoke test or spraying carb cleaner around intake gaskets while monitoring fuel trims.
Common cause - 6
Mass Air Flow (MAF) Sensor Failure
Low severityA dirty or faulty MAF sensor incorrectly measures incoming air, causing the PCM to deliver the wrong amount of fuel, resulting in misfires. Confirmed by checking MAF sensor data on a scan tool.
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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