P0300 on a 2019 Hyundai Elantra
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 Hyundai Elantra
Ranked from 243 NHTSA owner complaints filed for this vehicle.
- 1
Defective Piston Oil Rings / Cylinder Bore Scuffing
High severityImproperly heat-treated piston oil rings cause cylinder bore scuffing, leading to excessive oil consumption, loss of compression, and eventual engine failure. Look for excessive oil consumption, knocking noises, and loss of compression.
Reported in 10 NHTSA complaints - 2
Excessive Oil Consumption / Oil Starvation
High severityThe engine burns oil at an abnormally high rate without visible external leaks, leading to oil starvation, stalling, and catastrophic internal damage. Check the oil level frequently and look for signs of internal burning.
Reported in 9 NHTSA complaints - 3
Connecting Rod Bearing Failure / Crankshaft Wear
High severityPremature wear of the connecting rod bearings and crankshaft can cause severe engine knocking, metal shavings in the oil, and catastrophic engine failure (e.g., a thrown rod). Look for loud knocking noises, metal in the oil, or a hole in the engine block.
Reported in 6 NHTSA complaints - 4
Camshaft / Timing Gear Failure
High severityA broken pin on the camshaft or timing gear issues can cause the timing to jump, leading to misfires, stalling, and engine failure. Look for timing-related OBD2 codes and physical damage to the camshaft pin or gears.
Reported in 2 NHTSA complaints - 5
Faulty Spark Plugs
Low severityWorn or fouled spark plugs can fail to ignite the air-fuel mixture properly, causing random misfires. Inspect spark plugs for wear, carbon buildup, or oil fouling.
Common cause - 6
Faulty Ignition Coils
Medium severityA failing ignition coil will not provide sufficient voltage to the spark plug, leading to a misfire. Test the coils for proper resistance and check for visible damage or arcing.
Common cause - 7
Vacuum Leaks
Medium severityUnmetered air entering the intake manifold can cause a lean condition, resulting in random misfires across multiple cylinders. Inspect vacuum hoses and intake gaskets for leaks using a smoke machine.
Common cause - 8
Low Fuel Pressure / Faulty Fuel Injectors
Medium severityInadequate fuel delivery due to a weak fuel pump, clogged filter, or faulty injectors can cause lean misfires. Check fuel pressure and inspect injectors for proper operation and spray patterns.
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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