P0300High SeverityPowertrain

Random/Multiple Cylinder Misfire Detected

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

🔍 Fault Context

P0300 is one of the most common codes in the OBD2 database. The ECM measures crankshaft deceleration events to detect misfires. When multiple cylinders misfire, or the pattern is random across different cylinders, P0300 is set instead of a cylinder-specific code. Historical fault pattern data shows spark plugs, ignition coils, and fuel injectors account for over 80% of cases. However, a random misfire that moves between cylinders is a red flag for a deeper issue like low compression or a head gasket leak.

⚠️ 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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