The P0302 code identifies a misfire in cylinder 2, and the most common cause is an ignition problem on that cylinder—typically a faulty spark plug or a failing ignition coil/coil-on-plug. Other issues with fuel delivery, air intake, vacuum leaks, or compression can also trigger the code.
P0302 stands for “Cylinder 2 Misfire Detected.” When the engine control module detects that cylinder 2 did not fire as designed, the check engine light can come on and the vehicle may run roughly, lose power, or consume more fuel. In most cases, technicians start by checking the ignition components on cylinder 2, then move to fuel and air delivery if the problem isn’t found, and finally to compression if needed.
What P0302 Means
P0302 indicates a misfire specifically in cylinder 2. This means the spark, fuel, or air supply for that cylinder isn’t functioning as it should, or the cylinder isn’t sealing and building compression. Misfires can lead to rough idle, reduced acceleration, increased emissions, and poorer fuel economy.
Common causes of P0302
The following categories cover the most frequent culprits behind a cylinder 2 misfire. Inspect these areas first when diagnosing P0302.
Ignition system issues
- Worn or fouled spark plug in cylinder 2
- Faulty ignition coil or coil-on-plug for cylinder 2
- Damaged spark plug boot or lead causing weak or absent spark
When ignition components are the cause, replacing the spark plug and testing or swapping the coil(s) on cylinder 2 often resolves the misfire. If the replacement doesn’t fix the code, move on to fuel or air-delivery problems.
Fuel system issues
- Clogged or sticking fuel injector for cylinder 2
- Low fuel pressure or faulty fuel pump affecting cylinder 2
- Dirty injector spray pattern or improper injector operation
Fuel delivery problems can produce a lean or rich condition in cylinder 2, causing a misfire. Checking fuel pressure, injector operation, and related fuel circuitry is advised if ignition checks pass.
Air intake and vacuum leaks
- Vacuum leak around cylinder 2’s intake manifold or hoses
- Cracked or loose intake boot or ducting near cylinder 2
- Faulty PCV valve or hose increasing lean conditions
Air leaks or incorrect air/fuel ratios often present as misfires. A thorough check of intake plenums, hoses, and PCV systems helps identify leaks affecting cylinder 2.
Mechanical and compression issues
- Low compression in cylinder 2 due to worn piston rings or valve sealing
- Leaking exhaust or intake valves on cylinder 2
Mechanical problems generally require more involved testing, such as a compression or leak-down test, to confirm the cause and determine repairs.
How to diagnose P0302
Following a structured diagnostic approach helps pinpoint the root cause of a cylinder 2 misfire. The steps below reflect common automotive diagnostic practice.
- Review code data and freeze-frame information; note any related codes (e.g., P0300, P0301, P0303) and the misfire counter for cylinder 2.
- Inspect the ignition components on cylinder 2: remove and evaluate the spark plug, check the coil or coil-on-plug, and test the spark quality.
- Perform a spark test or swap the plug/coil with another cylinder to see if the misfire follows the component.
- Verify fuel delivery to cylinder 2: check fuel pressure against spec, test injector resistance, and listen for injector operation.
- Check for air leaks around cylinder 2: inspect vacuum lines, intake manifold gaskets, and PCV system; consider a smoke test if available.
- Conduct a compression test or leak-down test on cylinder 2 to assess mechanical health and valve seating.
- Review live data with a scan tool: monitor misfire counts, O2 sensor readings, and fuel trim behavior to confirm the issue is isolated to cylinder 2.
- Implement fixes based on findings, clear codes, and perform a road test to confirm no reoccurrence.
If the misfire persists after checking ignition and fuel delivery, mechanical issues may be present and professional diagnosis is recommended.
Repairs and prevention
Repair work is guided by the diagnosed cause. The following actions cover the most common fixes for P0302.
- Replace the spark plug on cylinder 2 and inspect/replace the plug boot if damaged
- Test and replace the ignition coil or coil-on-plug assembly for cylinder 2 as needed
- Repair or replace a faulty fuel injector for cylinder 2; address related wiring as necessary
- Repair vacuum leaks or cracked hoses and fix intake manifold/gasket issues near cylinder 2
- Address mechanical problems: repair/replace valves, repair head gasket, or perform a piston/ring repair if compression is too low
- Reset learned fuel trim values and re-test the vehicle to ensure the misfire does not reappear
After any repair, re-scanning and test driving are recommended to verify that cylinder 2 is firing correctly and that no new codes appear.
Summary
The P0302 code signals a misfire in cylinder 2. The most common cause is an ignition issue on that cylinder—typically a faulty spark plug or ignition coil—though fuel delivery, air leaks, and compression problems can also trigger the code. A systematic diagnosis, starting with ignition and progressing through fuel, air, and mechanical checks, helps pinpoint the exact cause and guide effective repairs. Regular maintenance, including spark plug and ignition checks, can help prevent P0302 from occurring.
How serious is a P0302 code?
The P0302 trouble code is considered serious. Some of the symptoms of this code make the operation of the vehicle dangerous. The vehicle may stop abruptly or stall out. In addition, damage to other engine components is possible if the trouble code is left unaddressed.
Can a P0302 damage my catalytic converter?
It's crucial to address error code P0302 because a misfiring cylinder can lead to various engine performance problems. Ignoring the issue can result in reduced fuel efficiency, increased emissions, and potential damage to the catalytic converter.
How much does it cost to fix a PO302 code?
Repair Cost Estimates for P0302 (2025)
| Repair | Parts Cost | Labor Cost |
|---|---|---|
| Spark plug replacement | $10-25 | $80-100 |
| Ignition coil replacement | $50-150 | $120-180 |
| Fuel injector cleaning/replacement | $100-300 | $200-400 |
| Compression/valve/head gasket repair | $500-1500+ | Varies |
Can a dirty air filter cause P0302?
Can a clogged fuel filter or dirty air filter cause a P0302 misfire code? Yes, a clogged fuel filter can restrict fuel flow to the engine, causing the vehicle to run lean. Similarly, a dirty air filter can restrict airflow and make the air-fuel mixture too rich, which can prevent proper ignition and cause misfires.