P0300 on a 2019 Nissan Altima
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 Nissan Altima
Ranked from 224 NHTSA owner complaints filed for this vehicle.
- 1
Blown Head Gasket / Coolant Leak into Cylinders
High severityCoolant leaks, overheating, and white smoke on startup indicate a blown head gasket, which allows coolant into the combustion chamber causing misfires.
Reported in 5 NHTSA complaints - 2
Internal Engine Failure / Metal in Oil Pan
High severityMetal shavings found in the oil pan indicate severe internal engine wear or failure, leading to poor performance, stalling, and misfires.
Reported in 3 NHTSA complaints - 3
Faulty Mass Air Flow (MAF) Sensor
Medium severityA failing MAF sensor causes incorrect air/fuel mixture calculations, resulting in rough idling, stalling, and random misfires.
Reported in 1 NHTSA complaint - 4
EGR Valve / Cooler Malfunction
Medium severityA malfunctioning EGR valve or cooler can introduce excessive exhaust gases into the intake, causing rough running and random misfires.
Reported in 1 NHTSA complaint - 5
Faulty Spark Plugs
Low severityWorn or fouled spark plugs fail to ignite the air/fuel mixture properly, leading to random or multiple cylinder misfires.
Common cause - 6
Faulty Ignition Coils
Medium severityWeak or failing ignition coils cannot provide sufficient voltage to the spark plugs, causing intermittent or consistent misfires across multiple cylinders.
Common cause - 7
Vacuum Leak
Medium severityUnmetered air entering the intake manifold leans out the air/fuel mixture, causing random misfires, especially at idle.
Common cause - 8
Low Fuel Pressure / Failing Fuel Pump
High severityInadequate fuel pressure starves the engine of fuel, leading to a lean condition and random misfires across all cylinders.
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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