P0300High SeverityPowertrain

Random/Multiple Cylinder Misfire Detected

Fault pattern analysis, verified repair data, and DIY cost breakdown

🔍 Fault Context

Random/Multiple cylinder Misfire Detected

⚠️ Symptom Mapping

  • •Rough idle, especially at stoplights
  • •Engine shaking or vibration
  • •Check engine light — may flash under load (serious)
  • •Poor acceleration
  • •Fuel economy drop
  • •Rotten egg smell from exhaust (catalyst damage)

📊 Generative Data Fixes

Ranked by historical repair data aggregates across verified fault reports

1. Worn spark plugs35%
2. Failed ignition coil (one or more)25%
3. Clogged or leaking fuel injectors15%
4. Vacuum leak causing lean misfire10%
5. Low compression (worn rings, bent valve)8%
6. Head gasket failure (coolant in combustion)7%

🔧 DIY Difficulty and Tools Required

DIY Difficulty Score

1
2
3
4
5
Intermediate (3/5)

Tools Required

OBD2 Scanner with misfire counterSpark plug socket (usually 5/8" or 9/16")Torque wrenchIgnition coil test light or swap-test coilsCompression tester

DIY Cost

$30 - $250

Shop Cost

$200 - $900

❓ Frequently Asked Questions

What does a flashing check engine light mean with P0300?

A flashing light means active, severe misfiring that is dumping raw fuel into the catalytic converter. Stop driving immediately or you risk a $1,500+ catalyst replacement.

How do I tell if it is a coil or a plug?

Swap the coil from the misfiring cylinder to a known-good cylinder. If the misfire follows the coil, the coil is bad. If it stays in the same cylinder, replace the plug.

Can bad gas cause P0300?

Yes. Water-contaminated or low-octane fuel can cause random misfires. Try a fresh tank of quality fuel if onset was sudden.

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