P0302: Cylinder 2 Misfire — Causes, Diagnosis & Repair Cost

The Short Answer

P0302 means your engine's computer has detected that cylinder 2 is misfiring — the code tells you which cylinder is the problem, not which part has failed.

What Is P0302 and How Does the ECM Catch It?

The OBD-II code P0302 stands for "Cylinder 2 Misfire Detected." Your engine control module doesn't have a dedicated misfire sensor — instead it watches the crankshaft position sensor. Every time a cylinder fires, it adds a small burst of torque that accelerates the crank slightly. When cylinder 2 misfires, the crank slows down at that exact firing interval. The ECM picks up on that RPM fluctuation and logs the code.

A 2–10% deviation triggers a steady Check Engine Light. Push past 10% and the light starts flashing, which is the car's way of telling you unburned fuel is getting into the exhaust and actively cooking the catalytic converter. At that point, pull over.

P0302 sits in the P030X family. P0300 is random/multiple misfires; P0301 through P0308 each finger a specific cylinder by that last digit. If you're seeing both P0300 and P0302, the random misfire might clear once cylinder 2 is fixed.

The 5 Most Common Causes of P0302

1. Faulty Ignition Coil

This is the first thing most experienced mechanics reach for, and there's a reason for that. The ignition coil takes 12 volts from your battery and steps it up to tens of thousands of volts to fire the spark plug. Coils fail gradually — they get heat-soaked, the windings crack, internal resistance climbs — and cylinder 2 starts misfiring under load before it misfires at idle. The swap test described in the FAQs above is clean and free to perform.

2. Worn or Fouled Spark Plug

A spark plug that's past its service life, oil-fouled, or cracked can't produce a consistent spark. Carbon buildup on the electrode increases the gap and resistance. Copper plugs wear faster than iridium or platinum — if yours are overdue, this is suspect number one before you even touch the coil.

3. Clogged or Stuck Fuel Injector

Cylinder 2 needs the right amount of fuel at the right time. A clogged injector restricts fuel delivery, leaning out that cylinder. A stuck-open injector floods it. Either way, combustion suffers and P0302 sets. Injector issues often show a longer crank time and rough cold starts alongside the misfire code.

4. Vacuum Leak Near Cylinder 2

Air sneaking in past a cracked intake boot, a loose manifold gasket, or a broken vacuum line leans out cylinder 2's air-fuel mixture. Spray carb cleaner carefully around intake runners while the engine idles — if the RPM changes, you found a leak. This cause gets overlooked because people assume misfires are always ignition-related.

5. Low Compression

If a leak-down test on cylinder 2 shows low compression, you're looking at something mechanical — worn piston rings, a burned valve, or a head gasket breach. This is the expensive scenario. Low compression can set P0302 even when the spark plug and coil are perfectly fine, because there's not enough pressure to create proper combustion.

How to Diagnose P0302 Step by Step

• Read all codes — note every DTC present, not just P0302. Multiple misfire codes or fuel trim codes change your diagnosis.
• Check the spark plug on cylinder 2 — pull it and inspect. Oil fouling, heavy carbon, a cracked insulator, or a worn electrode all point to plug replacement.
• Do the coil swap test — move the cylinder 2 coil to cylinder 3 (or any other). Clear codes and drive. If P0303 appears and P0302 goes away, replace the coil.
• Check for vacuum leaks — visual inspection first, then a smoke test or careful carb cleaner spray around intake runners at idle.
• Test fuel injector function — a mechanics stethoscope or an inexpensive injector tester can confirm the injector is clicking properly. A fuel trim reading above +10% long-term suggests a lean condition, possibly from an injector or vacuum leak.
• Compression test — if everything above checks out, do a dry and wet compression test on cylinder 2. A reading significantly lower than the other cylinders points to a mechanical issue.

In my experience, steps 2 and 3 catch the problem in the majority of P0302 cases. I'd estimate roughly 7 in 10 cylinder misfires come down to the plug or coil — start cheap before you go deep.

What Does It Cost to Fix P0302?

There's no single number here because the fix depends entirely on the root cause.

Don't let the wide range paralyze you. Start at the cheap end — a spark plug costs almost nothing to replace, and if it clears the code, you're done in an afternoon.

Ignition Coils: What to Look for When Buying

Not all replacement coils are equal. Coil-on-plug (COP) setups — which most modern engines use — put one coil per cylinder, so the coil gets exposed to combustion heat every time you drive. A replacement coil needs windings and insulation that can handle that thermal cycling long-term.

Look for a coil that matches OEM electrical specifications, fits your exact engine without adapter hacks, and comes with a real warranty. Buying a coil by price alone is a quick way to be back under the hood in a year.

For the right fit for your specific year, make, model, and engine, use the part finder below — it pulls current inventory and pricing so you're not guessing.

Can P0302 Damage My Engine If I Ignore It?

Yes, and it's not a small risk. Unburned fuel passing through cylinder 2 and into the exhaust stream does two things. First, it can wash down the cylinder walls with raw fuel, diluting the oil film and accelerating wear. Second, it superheats the catalytic converter — cats are designed to handle exhaust gases, not raw fuel combustion. A few extended drives with a severe misfire can destroy a catalytic converter that costs $500–$2,000+ to replace. That's not a scare tactic; it's just physics.

Fix the misfire. It's almost always cheaper than what happens if you don't.