P0300 on a 2015 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 2015 Hyundai Elantra
Ranked from 259 NHTSA owner complaints filed for this vehicle.
- 1
Excessive Oil Consumption / Internal Engine Wear
High severityThese engines are known to burn excessive oil, leading to low oil levels, internal wear (rod bearings, wrist pins), and subsequent misfires or catastrophic engine failure.
Reported in 6 NHTSA complaints - 2
Timing Chain Stretch or Failure
High severityA loose or failing timing chain disrupts engine timing, causing random misfires (P0300) and rough running, and can lead to engine stalling or failure.
Reported in 2 NHTSA complaints - 3
Ignition Coil Failure
Medium severityA faulty ignition coil is one of the most common causes of a P0300 random misfire code, often leading to rough running and flashing check engine lights.
Common cause - 4
Spark Plug Wear or Failure
Low severityWorn or fouled spark plugs fail to ignite the air/fuel mixture properly, causing random or multiple cylinder misfires.
Common cause - 5
Vacuum Leak
Medium severityUnmetered air entering the intake manifold leans out the air/fuel mixture, causing random misfires across multiple cylinders.
Common cause - 6
Fuel Injector Failure or Clogging
Medium severityClogged or failing fuel injectors prevent the correct amount of fuel from entering the cylinders, leading to lean misfires.
Common cause - 7
Low Fuel Pressure
Medium severityA failing fuel pump or clogged fuel filter can cause low fuel pressure, starving the engine of fuel and causing random misfires.
Common cause - 8
Mass Air Flow (MAF) Sensor Failure
Medium severityA dirty or faulty MAF sensor provides incorrect airflow data to the PCM, resulting in an improper air/fuel mixture and random misfires.
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.
Rather have a pro handle it? Find a vetted local mechanic.