P0302: Cylinder 2 Misfire — What to Check First

P0302 — cylinder 2 misfire detected. Same family as P0301, same basic approach: isolate the cause to that specific cylinder. Start with a coil/plug swap test (covered in detail in the P0301 article). If the misfire does not follow the coil or plug, you are likely looking at an injector or compression problem.

This article focuses on injector diagnostics — the step most techs rush through or skip entirely.

What This Code Actually Means

The PCM detected repeated misfire events on cylinder 2's power stroke via crankshaft position sensor analysis. The diagnostic logic is identical to any single-cylinder misfire code: the crank does not accelerate as expected when cylinder 2 should be contributing power. The code sets after the misfire count exceeds the PCM's threshold over a calibrated number of engine revolutions.

Common Causes

• Ignition coil or spark plug: Still the most common. Do the swap test first — always.
• Fuel injector — electrical: Open or shorted injector coil, corroded connector, or PCM driver circuit failure.
• Fuel injector — mechanical: Clogged nozzle, stuck pintle, or leaking O-ring causing external fuel leak or loss of spray pattern.
• Low compression: Burned valve, broken valve spring, piston ring failure, or head gasket leak on cylinder 2.
• Wiring / connector: Corroded or backed-out pins at the injector connector. Particularly common on engines where the injector harness runs near heat sources.

Diagnostic Approach: Injector Testing

Assuming you have already done the coil/plug swap test and the misfire stays on cylinder 2, here is how to work the injector side:

Step 1: Noid Light Test

Unplug the cylinder 2 injector connector and install a noid light. Crank or run the engine. The noid light should flash consistently — this confirms the PCM is sending the injector pulse signal and the wiring from the PCM to the connector is intact. No flash = wiring or PCM driver issue, not the injector itself.

Step 2: Injector Resistance

Measure the injector coil resistance with a DVOM across the two pins. Compare to spec (typically 11–18 ohms for high-impedance injectors, 2–5 ohms for low-impedance). An open reading or a reading significantly outside spec means the injector coil is failed.

Step 3: Injector Balance Test

This is the money test for clogged injectors. Using a scan tool or dedicated injector pulse tool, fire each injector individually for a calibrated pulse width and watch the fuel pressure drop on a gauge. Each injector should drop pressure by the same amount (within 1–2 PSI). If cylinder 2's injector drops significantly less than the others, it is restricted. If it drops more, it may be leaking.

Step 4: Scope the Injector Waveform

For intermittent injector issues, scope the injector drive signal. You are looking at:

• Command voltage: Battery voltage on the high side when the injector is commanded off.
• Pull-in spike: Voltage drops to near zero when the driver opens — this is the injector energizing.
• Inductive kick: The voltage spike when the driver closes and the injector coil's magnetic field collapses. This spike should be 60–80V on most systems. A low or absent inductive kick indicates a shorted coil or pintle that is not moving (stuck open or stuck closed).

Compare the cylinder 2 waveform to a known-good cylinder. Differences in pulse width, peak voltage, or ramp profile tell you exactly what is wrong.

Step 5: Injector Swap

If electrical tests pass but you still suspect the injector, swap it with another cylinder. If the misfire follows the injector, replace it. On GDI systems, this requires depressurizing the fuel rail first — high-pressure fuel (2,000+ PSI) is not something you want to release unexpectedly.

Common TSBs and Pattern Failures

• Hyundai/Kia GDI (Theta II, Nu, Gamma): Carbon buildup on intake valves is endemic to these engines. The misfire may show up as a single-cylinder code even though all valves are carboned — one cylinder just hits the threshold first. Walnut blast the intake valves and expect the others to follow if not cleaned.
• BMW N54/N55 direct injection: Injector failures are a known pattern. BMW has revised the injector part number multiple times. Index 12 or later injectors are the current recommended replacement. If one fails, inspect them all.
• Chrysler 3.6L Pentastar: Fuel injector failures and rocker arm issues are documented on 2011–2013 models. Check for TSBs specific to the model year — some include updated injectors.
• Ford EcoBoost (all variants): Injector seal leaks can cause a single-cylinder misfire with a fuel smell at the valve cover area. Check for external fuel leaks around the injector bore before going internal.

Injector diagnostics take a little more time than the swap test, but they give you definitive answers. A noid light, a DVOM, and a fuel pressure gauge are all you need for 90% of injector-related misfires. For the other 10%, a scope tells the rest of the story. Need help interpreting what you are seeing? APEX Tech's AI Diagnostics can walk through the data with you.