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P0300

P0300 on a 2016 Hyundai Tucson Fuel Cell

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 2016 Hyundai Tucson Fuel Cell

Ranked from 1,536 NHTSA owner complaints filed for this vehicle.

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  1. 1

    Worn piston rings / low compression from chronic oil consumption (Theta II engine defect)

    High severity

    An unusually large share of this batch describes abnormal oil consumption, rough running, and stalling tied to the well-documented Hyundai/Kia Theta II engine defect (subject of a class-action settlement); rings worn from oil-starved cylinders lose compression and misfire.

    Reported in 15 NHTSA complaints
  2. 2

    Rod bearing failure / engine knock (end-stage of the same Theta II defect)

    High severity

    Several owners describe a sudden violent knock followed by engine shutdown and a rod-bearing diagnosis, with dealers saying they see this at least once a week on these engines; the resulting mechanical damage produces severe multi-cylinder misfire before total failure.

    Reported in 5 NHTSA complaints
  3. 3

    Worn spark plugs / failing ignition coils

    Medium severity

    Several complaints describe spark plugs and/or ignition coils being replaced in an attempt to fix a rough-running, misfiring engine.

    Reported in 3 NHTSA complaints
    Parts:spark plugsignition coils
  4. 4

    Dealer-confirmed random/multi-cylinder misfire

    High severity

    At least one complaint explicitly documents a dealer-confirmed 'random misfire on all cylinders with a dead miss on 4' alongside oil consumption, tying the electrical and mechanical symptoms together.

    Reported in 2 NHTSA complaints
  5. 5

    Leaking or clogged fuel injector

    Medium severity

    One owner reported a fuel-injector issue coinciding with the check-engine light and a no-start condition.

    Reported in 1 NHTSA complaint
    Parts:fuel injector
  6. 6

    Vacuum or intake leak

    Medium severity

    A cracked intake boot or loose vacuum line leans out one or more cylinders, producing a misfire most noticeable at idle.

    Common cause
  7. 7

    EGR valve stuck open or flow fault

    Low severity

    Excess exhaust gas recirculated at the wrong time dilutes the intake charge enough to cause a misfire, especially at idle/light load.

    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