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P0300

P0300 on a 2019 Hyundai Tucson

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 Tucson

Ranked from 370 NHTSA owner complaints filed for this vehicle.

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  1. 1

    Low compression / worn piston rings from chronic oil consumption (Theta II GDI engine defect)

    High severity

    Numerous owners report the engine burning a quart or more of oil every 1,000-1,500 miles; the resulting ring wear and reduced compression is a documented driver of misfire on this engine family.

    Reported in 9 NHTSA complaints
  2. 2

    Connecting rod bearing failure / catastrophic bottom-end failure

    High severity

    Several complaints describe sudden engine seizure or a confirmed rod-bearing failure (including a cylinder-3 rod bearing failure), part of the well-documented Theta II recall/lawsuit history that can present as a severe misfire just before failure.

    Reported in 6 NHTSA complaints
  3. 3

    Faulty knock sensor / knock-sensor detection logic (KSDS) triggering limp mode

    Medium severity

    Several owners had the vehicle enter reduced-power/limp mode tied to a knock-sensor code or the factory knock-sensor recall, which can accompany or be mistaken for misfire symptoms.

    Reported in 3 NHTSA complaints
    Parts:knock sensor
  4. 4

    Worn spark plugs or failing ignition coils

    Medium severity

    One owner had spark plugs and coils replaced twice for a recurring cylinder-3 misfire, confirming this as an active failure point on this vehicle.

    Reported in 1 NHTSA complaint
    Parts:spark plugsignition coils
  5. 5

    Vacuum or intake leak

    Medium severity

    An unmetered air leak at a hose, gasket, or PCV fitting leans out one or more cylinders enough to cause a random misfire.

    Common cause
  6. 6

    Clogged or leaking fuel injector(s)

    Medium severity

    A partially clogged or dribbling injector starves or floods a cylinder, producing a repeatable misfire on that cylinder.

    Common cause
    Parts:fuel injectors
  7. 7

    Carbon-fouled intake valves

    Medium severity

    Direct-injection engines like this one have no fuel washing the intake valves, so carbon buildup can disrupt airflow/combustion on individual cylinders over time.

    Common cause
  8. 8

    EGR valve fault

    Low severity

    A stuck-open or leaking EGR valve dilutes the intake charge unevenly and can push individual cylinders into a misfire.

    Common cause
    Parts:EGR valve

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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

1

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.

2

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.

3

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.

4

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.

5

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 RoughFlashing Check Engine Light