P0300 - Random/Multiple Cylinder Misfire Detected
System
Powertrain (Engine & Gearbox)
Technical Description
The Engine Control Module (ECM) calculates micro-acceleration variations of the crankshaft reluctor wheel and detects incomplete or absent combustion events across multiple cylinders randomly. A flashing Check Engine Light signals catalyst-damaging misfire levels requiring immediate shutdown.
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Ignition Coil Primary Voltage (Terminal 15) | Voltage (V) | 12.0 - 14.4 V | Ignition ON and idling |
| Ignition Coil Dwell Primary Current | Current (A) | 6.0 - 12.0 A peak | Current clamp on coil power feed |
| Fuel Injector Resistance (High-Z) | Resistance (Ω) | 11.5 - 15.5 Ω | Disconnected connector at 20°C |
Ignition ON and idling
Current clamp on coil power feed
Disconnected connector at 20°C
Oscilloscope Waveform Analysis
500 µs/div, 50 V/divPossible Causes
Worn, fouled, or incorrectly gapped spark plugs
Failing ignition coil packs or secondary breakdown
Major intake vacuum leak affecting all cylinders
Low fuel rail pressure or intake valve carbon buildup
Symptoms
Recommended Solution
Shut off engine if MIL is flashing.
Inspect spark plugs and coils across all cylinders.
Measure compression and fuel rail pressure.
Mechanic's Tip
Ignition misfires peak under high load at low RPM (WOT in high gear at 1500 RPM) because dense cylinder charge demands maximum voltage to spark.
Common Combinations
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