P0302 — Cylinder 2 Misfire Detected

Quick answer

• What the P0302 code means: The engine control module (ECM) has detected that cylinder 2 is not firing correctly, indicating a misfire.
• Severity: Moderately severe. You can likely drive home, but prolonged driving can damage the catalytic converter or other engine components.
• Most common cause: A faulty spark plug or ignition coil for cylinder 2.

What the P0302 code means

The P0302 diagnostic trouble code (DTC) officially stands for "Cylinder 2 Misfire Detected". In simpler terms, this means that the engine's computer (the ECM/PCM) has identified that cylinder number 2 is not contributing its fair share of power to the engine. When a cylinder misfires, it means the air/fuel mixture inside that cylinder is not igniting properly or consistently. This can be due to a lack of spark, an incorrect air/fuel mixture, or a lack of compression.

The ECM monitors the crankshaft's rotational speed. During normal operation, each cylinder firing contributes a surge in speed. If the ECM detects a significant drop in acceleration during the power stroke of cylinder 2, it registers a misfire. If misfires are significant enough to potentially damage the catalytic converter, the Check Engine Light will flash.

Common symptoms

• Check Engine Light (typically flashing during active misfire): The most obvious indicator.
• Rough running engine: The engine may shake, vibrate, or feel like it's sputtering, especially at idle or under acceleration.
• Reduced engine power: The vehicle may feel sluggish or have difficulty accelerating.
• Poor fuel economy: Incomplete combustion wastes fuel.
• Engine hesitation or stumble: The engine may briefly lose power, particularly when accelerating.
• Strong fuel smell from the exhaust: Unburnt fuel can exit the exhaust.
• Difficulty starting (less common, but possible with severe misfires).

Common causes

1. Faulty Spark Plug - Cylinder 2: This is the most frequent cause. A worn, fouled, or damaged spark plug cannot generate an adequate spark to ignite the air/fuel mixture.
2. Defective Ignition Coil - Cylinder 2: The ignition coil delivers high voltage to the spark plug. If the coil fails, the spark plug won't receive the necessary voltage.
3. Clogged or Faulty Fuel Injector - Cylinder 2: A fuel injector that isn't delivering enough fuel (or too much) to cylinder 2 will cause a lean or rich condition, leading to a misfire.
4. Vacuum Leaks: Leaks in the intake manifold gasket, vacuum hoses, or PCV system can lean out the air/fuel mixture, affecting one or more cylinders, including cylinder 2.
5. Low Compression - Cylinder 2: This is a more severe issue, often indicating internal engine problems such as worn piston rings, burnt valves, or a blown head gasket. The cylinder simply cannot build enough pressure for efficient combustion.
6. Faulty Spark Plug Wires (older vehicles): For vehicles with traditional spark plug wires, a damaged or worn wire can prevent spark from reaching the plug.
7. ECM/PCM Issues: While rare, a faulty engine control module can sometimes incorrectly report a misfire or fail to properly control ignition or fuel systems. This is usually diagnosed after all other possibilities are ruled out.

How a technician diagnoses it

1. Verify the code and check for other DTCs: A technician will connect an OBD-II scan tool to confirm the P0302 code and look for any related codes (e.g., fuel trim codes, random misfire codes). They will also note if the Check Engine Light is flashing.
2. Inspect live data: Using a scan tool, they will monitor live misfire counters for all cylinders. This helps confirm that cylinder 2 is consistently misfiring and if other cylinders are also experiencing issues (which might point to a broader problem).
3. Check freeze-frame data: The technician will examine the freeze-frame data, which is a snapshot of engine conditions (engine speed, load, temperature, etc.) at the moment the P0302 code was set. This can provide clues about when the misfire occurs.
4. Confirm spark delivery:
   • Spark plug inspection: Remove and visually inspect the spark plug from cylinder 2. Look for signs of fouling, wear, damage, or improper gap. Compare it to other cylinders.
   • Ignition coil test: Test the ignition coil for cylinder 2. This can involve swapping the coil to another cylinder to see if the misfire follows the coil. A coil on plug (COP) spark tester can also be used to check for spark directly.
   • Fuel injector test: Using a stethoscope to listen for the clicking of the injector, or performing a fuel pressure drop test, or even a basic resistance check, can indicate a faulty injector. Swapping injectors to another cylinder can also confirm if the issue moves.
5. Check fuel delivery: Conduct a fuel pressure test to ensure adequate fuel pressure to the rail. The fuel pressure should be within the manufacturer