P0300 on a 2015 Hyundai Sonata

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 Sonata

Ranked from 1,128 NHTSA owner complaints filed for this vehicle.

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1
Connecting rod bearing failure / Engine seizure
High severity
The Theta II engine is known for connecting rod bearing failure, leading to engine knock, stalling, and complete engine seizure. This can cause misfires and a flashing check engine light before or during failure.
Reported in 10 NHTSA complaints
2
Excessive oil consumption / Low oil level
High severity
Severe oil consumption can lead to low oil levels, causing internal engine damage, loss of compression, and misfires. Look for fouled spark plugs and low oil on the dipstick.
Reported in 4 NHTSA complaints
3
Low engine compression / Internal engine failure
High severity
Internal engine wear or damage (such as piston/ring failure) leads to low compression in one or more cylinders, resulting in a misfire. Confirmed via a compression or leak-down test.
Reported in 2 NHTSA complaints
4
Faulty spark plugs or ignition coils
Low severity
Worn or fouled spark plugs and failing ignition coils are the most common generic causes of a P0300 code. Confirmed by inspecting the spark plugs for wear/fouling and testing coil operation.
Common cause
5
Vacuum leak / Intake manifold leak
Medium severity
Unmetered air entering the engine leans out the air/fuel mixture, causing random misfires. Confirmed by checking fuel trims and performing a smoke test on the intake system.
Common cause
6
Fuel delivery issue (Low fuel pressure / Clogged injectors)
Medium severity
A failing high-pressure fuel pump (HPFP) or clogged GDI injectors can starve the engine of fuel, leading to lean misfires. Confirmed by checking fuel pressure data and injector balance.
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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Matching symptoms

Car Runs Rough Flashing Check Engine Light