The P0302 code means cylinder 2 is misfiring. In most cases, the fix starts with the ignition system, then the fuel delivery to that cylinder, followed by checks for leaks or mechanical issues. After identifying the culprit, you’ll replace parts as needed and verify the fix with a road test.
What P0302 Means
P0302 is a generic OBD-II trouble code that signals a misfire in cylinder 2. It can be caused by a failing spark plug, ignition coil, or fuel injector, as well as vacuum leaks, wiring problems, or mechanical issues such as low compression. In some vehicles it may appear alongside other misfire codes like P0300 (random/multiple misfires) or P0301/P0303 for neighboring cylinders.
Diagnostic approach
To identify the right fix, start with a structured diagnostic approach. The following steps help determine whether the problem is electrical, fuel-related, or mechanical.
- Verify the code and data with a scan tool. Confirm P0302 and review freeze-frame data and the cylinder-specific misfire counter if available.
- Inspect the cylinder 2 spark plug for wear, fouling, or incorrect gap. Replace if needed and note the condition of the plug.
- Test the ignition coil for cylinder 2. Swap the coil or coil pack with another cylinder to see if the misfire follows the component, indicating a faulty coil.
- Check the wiring and connectors to the ignition coil for damage, corrosion, or loose connections.
- Examine the fuel injector for cylinder 2. Measure its resistance against spec and verify it is receiving a signal. Listen for injector click with engine idling if possible.
- Confirm fuel pressure and rail integrity. Low or inconsistent pressure can cause cylinder-specific misfires.
- Look for vacuum leaks around cylinder 2, including intake manifold gaskets and PCV hoses. A smoke or aerosol leak test can help locate leaks.
- Perform a compression or leak-down test on cylinder 2 to assess mechanical health (valves, piston rings, head gasket, or cylinder wall).
- Check for related sensor issues (MAF/MAP, oxygen sensors) or software/ ECU updates that can affect fueling and ignition, especially on newer vehicles.
Once you identify the likely cause from these checks, you can target repairs more precisely instead of replacing parts randomly.
Common fixes by cause
Based on the diagnostic findings, these are typical repairs that address the most common P0302 causes. If you’re not comfortable performing these steps, consult a professional mechanic.
- Replace the cylinder 2 spark plug if it is worn, fouled, or has an improper gap.
- Replace or swap the cylinder 2 ignition coil if it tests weak or shows intermittent failure.
- Clean or replace the cylinder 2 fuel injector. Check fuel delivery and injector seals or O-rings; ensure proper fuel pressure.
- Repair vacuum leaks around cylinder 2, such as the intake manifold gasket or cracked hoses. A smoke test can help locate leaks.
- Repair or replace damaged wiring or connectors to the coil and injector; repair or replace damaged harness sections.
- Address mechanical issues if compression tests reveal low compression on cylinder 2 (valve seating, piston rings, head gasket). This is a more involved repair.
- Update ECU software or apply manufacturer-recommended recalls/TSBs related to misfires, if applicable.
- Ensure proper fuel pressure and perform a general fuel system inspection to rule out upstream causes.
After performing the repairs, clear the codes and re-test the system to confirm the misfire is resolved. If P0302 returns or if another cylinder shows a misfire, re-run the diagnostic steps for a full assessment.
Post-repair testing and verification
Once repairs are completed, run a structured verification to ensure the issue is resolved and there’s no collateral damage.
- Clear all codes with a scan tool and reset readiness monitors if your vehicle requires it.
- Start the engine and bring it to operating temperature while monitoring live data for the cylinder 2 misfire counter and ignition timing.
- Take a road test under varying speeds and loads to reproduce normal operating conditions and confirm there is no continued misfire.
- Re-scan for codes and verify that P0302 does not return and that no new codes appear.
- Inspect spark plug, coil, and injector connections again during a cool engine state to verify there are no loose connections.
- If misfires recur, revisit compression and fuel delivery tests or seek professional diagnostics, as there could be a deeper mechanical issue.
Proper verification helps prevent returning misfires and protects the catalytic converter from damage due to repeated misfiring.
Summary
P0302 identifies a misfire in cylinder 2. Start with the ignition system (spark plug and coil), then verify fuel delivery and any vacuum leaks, and finally check mechanical health (compression). Use a systematic diagnostic approach, perform targeted repairs, and re-test to confirm the fix. If you’re ever unsure, consult a qualified technician to avoid unintended damage.