P03B2 — Cylinder 3 Combustion Performance

Diagnostic algorithm

1. Connect a scan tool and record freeze frame and live data (misfire counters, cylinder contribution, fuel trims, injector pulse widths, fuel pressure). Note whether code is continuous or intermittent.
2. Visually inspect spark plug, coil/boot/wire and injector connector at cylinder 3 for damage, oil, carbon tracking, corrosion or loose pins. Repair as needed.
3. Check battery voltage and charging system while cranking; low voltage can cause misfires. Ensure good ground connections.
4. Swap ignition coil (or coil pack) from cylinder 3 with a known good cylinder. Re-scan for codes or misfire change. If fault follows coil, replace coil.
5. Swap or temporarily swap the injector from cylinder 3 with another cylinder and monitor misfire counters. If fault follows injector, replace injector.
6. Measure injector resistance and compare to spec; backprobe injector with scope or noid light to confirm correct injector drive and pulse width.
7. Measure primary and secondary ignition waveforms with oscilloscope while cranking/idle to inspect spark energy and timing.
8. Measure static cranking compression on cylinder 3 and compare with other cylinders. If low or notably different, perform a leak-down test to identify source (rings, valves, head gasket).
9. Check fuel rail pressure and regulator operation under load; verify fuel pressure holds during cranking and no large drops under load.
10. Inspect for intake manifold gasket leaks or vacuum leaks near cylinder 3 (use smoke test or propane/soapy water method while monitoring RPM/AFR).
11. If mechanical and component tests pass, review cam/crank timing (timing belt/chain stretch/slip, variable valve timing operation) and confirm correct phasing.
12. If all vehicle-specific tests are normal, consider ECM/software updates or intermittent wiring faults; consult service information and wiring diagrams before replacing the PCM.