P0302 Code: Cylinder 2 Misfire Detected

What the P0302 code means

The computer watches the instantaneous speed of the crankshaft. When a cylinder does not burn properly, the crankshaft loses acceleration for a few specific degrees of rotation, and the system works out which cylinder it happened in.

The P0302 code points to cylinder two. Compared with a P0300, which means misfires spread around and points to a cause common to the whole engine, the problem here is narrowed down: only four things can fail on an individual cylinder, and they are spark, fuel, air and compression.

The work order goes from the cheapest part to the most expensive, and the main tool costs nothing: swap parts between cylinders and see whether the misfire moves to a new location.

There is one piece of data your scan tool offers that almost nobody looks at: the misfire counter for each cylinder. Even though the code names cylinder two, that counter shows how many misfires each cylinder has racked up, and it often reveals a second cylinder with high numbers that has not yet triggered its own code.

When that happens, the cause stops being a single component and becomes something shared: fuel pressure, valve timing or a vacuum leak that affects several cylinders at once. Looking at that counter before you take anything apart keeps you from replacing a coil that was never bad.

P0302 code symptoms

• Check engine light flashing while the misfire is happening, or steady if it has already stopped.
• Vibration at idle that you can feel in the steering wheel and the shifter.
• Loss of power and jerking when you accelerate.
• Rough idle and hard starting.
• Smell of unburned gas at the tailpipe.
• Higher fuel consumption.
• A high misfire counter on another cylinder as well, even though its code has not set.
• Vibration that changes in intensity with engine temperature.

Likely causes of the P0302 code

1. Cylinder 2 spark plug worn, with the wrong gap or soaked in oil.
2. Weak ignition coil on that cylinder. It usually fails under load before it fails at idle.
3. Spark plug wire leaking to ground on engines that still use them.
4. Clogged injector or one with a damaged electrical circuit.
5. Localized vacuum leak in the intake runner for that cylinder.
6. Low compression from a burned valve or worn piston rings.
7. Head gasket leaking into the cylinder or into the coolant.
8. Camshaft with a worn lobe on high-mileage engines.
9. Vacuum leak shared between neighboring cylinders from a deteriorated intake gasket.
10. Insufficient fuel pressure, which hits the cylinder with the most worn injector first.
11. Spark plug with a worn-down electrode from too many miles, which fails sooner than the others.

How to diagnose the P0302 code step by step

1. Identify cylinder 2 from the layout diagram for your engine. Numbering does not always start on the belt side.
2. Swap the coil with the one from another cylinder, clear the code and drive. If the other cylinder code appears, the coil is the culprit.
3. Repeat the test with the spark plug. It is free and rules the part in or out with certainty.
4. Read the look of the spark plug. Wet with oil points to rings or valve guides, wet with gas points to a lack of spark, and white and eroded points to a lean mixture or overheating.
5. Swap the injector if the spark plug and coil have been ruled out.
6. Measure compression on the cylinder and compare it with the rest.
7. Run a leak-down test if compression is low, to learn whether the air escapes past the valves, past the rings or into the cooling system.
8. Check the misfire counter for each cylinder in live data. If another cylinder is piling up misfires without a code, the cause is shared.
9. Measure fuel pressure under load, not only at idle. A weak pump only gives itself away when it is asked for flow.
10. Apply smoke to the intake to find leaks that affect the runners of neighboring cylinders.

How to fix the P0302 code

• Replace the spark plug, preferably the whole set, with the part number and gap the manufacturer specifies.
• Replace the faulty ignition coil. If the engine has high mileage and one has already failed, consider replacing all of them.
• Replace the deteriorated spark plug wire.
• Clean or replace the injector with insufficient flow.
• Repair the vacuum leak in the affected runner.
• Recondition the valves or repair the cylinder head when compression confirms a mechanical problem.
• Replace the intake manifold gasket if the smoke test shows a leak at the affected runners.
• Change the fuel filter and check the pressure again before you suspect the injectors.
• Renew the full set of spark plugs if the mileage is past the service interval, even if only one has failed.

Technical reference data

• Expected compression: 10 to 14 bar (145 to 200 psi), with a maximum difference of 10 percent between cylinders.
• Typical ignition coil primary resistance: 0.5 to 2 ohms. Secondary: 6,000 to 15,000 ohms.
• Typical resistance of a port fuel injector: 12 to 16 ohms.
• Spark plug gap: 0.7 to 1.1 millimeters (0.028 to 0.043 inch), depending on the engine.
• Misfire counter for each cylinder: useful for spotting affected cylinders that have not yet set their own code.
• Approximate fuel pressure under load: 3 to 4 bar (45 to 58 psi), with no drop when you accelerate.
• Usual spark plug replacement interval: 30,000 km (about 18,000 miles) for nickel plugs and 100,000 km (about 62,000 miles) for platinum or iridium plugs.

Brand-specific notes

Always verify the cylinder numbering in the vehicle documentation. Working on the wrong cylinder is a common mistake that wastes time and parts, especially on V-type engines.

A single-cylinder misfire that shows up shortly after you fill the tank usually points to the fuel and not the engine. If it lines up with a change of gas station, empty the tank before you take components apart.

Frequently asked questions about P0302