P0303 - Cylinder 3 Misfire
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Cylinder 3 Misfire (P0303). The fault is isolated to cylinder 3, positioned in the central engine thermal core. This directly impacts individual cylinder volumetric efficiency, firing synchronization, and dedicated harness branch loading.
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Cylinder 3 Ignition Coil – Primary Resistance | Resistance (Ω) | 0.4 - 2.0 Ω | Coil disconnected at 20°C (cylinder 3) |
| Cylinder 3 Ignition Coil – Supply Voltage | Voltage (V) | 11.8 - 14.4 V | Ignition ON at coil B+ pin |
| Cylinder 3 Ignition Coil – ECM Dwell Trigger Pulse | Voltage (V) | Rest ≈ battery voltage, dwell pull to 0 V for 1.5 - 4.0 ms | Engine running or cranking |
Coil disconnected at 20°C (cylinder 3)
Ignition ON at coil B+ pin
Engine running or cranking
Oscilloscope Waveform Analysis
500 µs/div, 50 V/divPossible Causes
Cylinder 3 Misfire is electrically operational but performing outside calibrated tolerance
Thermal core hotspot (cylinder 3):Peak engine operating temperatures due to Siamese exhaust port layout and restricted coolant jacket passages.
Exhaust radiant heat embrittlement:Central manifold radiant heat degradation causing dielectric breakdown of cylinder 3 harness insulation.
Chafed or pinched wiring harness along the signal path to Cylinder 3 Misfire
Internal mechanical wear or carbon deposits inside Cylinder 3 Misfire
Defective internal output driver or reference circuit in the control module for Cylinder 3 Misfire
Symptoms
5
Recommended Solution
Swap component on cylinder 3 over to cylinder 4 and clear DTCs to confirm if fault follows.
Measure component internal coil resistance both cold (20°C) and immediately after hot soak (95°C) to catch thermal open circuit.
Verify underlying mechanical operation and rule out blockage, vacuum leaks, or mechanical binding.
Verify loaded supply voltage and harness terminal pins at Cylinder 3 Misfire.
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Cylinder 3 Misfire.
Inspect spark plug gap and ceramic insulator for carbon tracking, cracks, or dielectric puncture.
Mechanic's Tip
Pro-tip for cylinder 3: Cylinder 3 is the thermal core of the engine block. A component testing within spec cold (20°C) may only fail once thermal saturation occurs (95°C).