P0300 on a 2012 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 2012 Hyundai Sonata
Ranked from 1,552 NHTSA owner complaints filed for this vehicle.
- 1
Connecting rod bearing failure / Engine seizure
High severityThe Theta II engine is known for premature rod bearing wear, metal debris, and complete engine seizure. Look for loud knocking, sudden loss of power, and failed bearing clearance tests.
Reported in 17 NHTSA complaints - 2
Knock sensor / KSDS system fault
Medium severityThe Knock Sensor Detection System (KSDS) update can trigger limp mode or codes (like P1326 or P0326) indicating combustion vibration or bearing wear. Confirm by checking for KSDS codes and sensor circuit performance.
Reported in 3 NHTSA complaints - 3
Excessive oil consumption / Oil starvation
High severityThe engine consumes oil rapidly without warning lights, leading to low oil levels and subsequent engine failure or seizure. Check oil levels and monitor consumption rates.
Reported in 2 NHTSA complaints - 4
Engine wiring harness damage
High severityDamage to the engine wiring harness, sometimes occurring during engine replacement, can cause communication loss and driveability issues. Inspect the harness for physical damage or poor connections.
Reported in 1 NHTSA complaint - 5
Faulty spark plugs
Low severityWorn or fouled spark plugs are a primary cause of misfires. Inspect the spark plugs for wear, carbon buildup, or incorrect gap.
Common cause - 6
Defective ignition coils
Medium severityFailing ignition coils cannot provide sufficient voltage to the spark plugs, resulting in misfires. Test coil resistance and check for proper operation.
Common cause - 7
Vacuum leaks
Medium severityUnmetered air entering the intake manifold leans out the air/fuel mixture, causing random misfires. Inspect vacuum hoses and intake gaskets for leaks.
Common cause - 8
Low fuel pressure / Failing fuel pump
Medium severityInadequate fuel pressure prevents proper fuel delivery, leading to a lean condition and misfires. Test fuel pressure at the rail to confirm.
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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