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P0302 Fault on 2006 Chevy HHR 2.4L - Diagnosis After Spark Plugs, Coils, and Fuel Injectors Replacement

Model: 2006 Chevy HHR Fault Code: P0302 Posted: 2018-02-20 16:44

I'm experiencing a persistent P0302 cylinder 2 misfire code on my 2006 Chevrolet HHR with the 2.4L engine. The check engine light remains illuminated even after replacing all components in this order: spark plugs, ignition coils, and fuel injectors. The vehicle shows no symptoms of power loss, hard starting, or hesitation. However, I noticed a drop in fuel efficiency to approximately 16.5 MPG post-fuel injector replacement. Additionally, the OBD-II code P0449 (Solenoid Circuit Malfunction) appeared after installing the injectors. I'm seeking reliable troubleshooting steps and insights into potential root causes. Any advice on how to proceed would be greatly appreciated.

Related fault codes
P0302
Comments (3)
Anonymous 2018-02-21 07:23

A cylinder misfire can stem from several sources: 1) Ignition system – What did the old #2 spark plug look like? Did you install AC Delco plugs? Are the ignition coils firing properly? 2) Fuel delivery – You replaced the fuel injector; consider using a noid light to verify signal presence on cylinder 2. 3) Mechanical issues – Perform a compression test and inspect for vacuum leaks at cylinder 2. For reference: https://www.obd-codes.com/p044-9 Note: P0449 relates to evaporative emissions system malfunctions, which may indirectly cause vacuum fluctuations. Pay close attention to the keywords in this code.

Anonymous 2018-02-21 09:36

The #2 spark plug appeared in good condition when removed and was replaced with AC Delco plugs. The vehicle runs smoothly now, suggesting that ignition coils are likely firing correctly. I'm unfamiliar with a noid light—will need to research this further. For a compression test, will I have to take the car to a professional shop? As a weekend mechanic, I don't own all the necessary diagnostic tools. Thanks for your guidance.

Anonymous 2018-02-21 09:53

If the vehicle is running fine yet P0302 persists, it's worth checking if you have an OBD-II scanner. Before investing in further diagnostics, try simple and fast tests first: - Swap ignition coil #2 with a known-good coil from another cylinder. If the code follows the new coil, it points to a faulty coil. - Avoid using oiled air filters (e.g., K&N types), as they can interfere with engine performance. For P0449: Focus on resolving the evaporative emissions system issue. Clear the fault codes and drive the vehicle under normal conditions. If no code appears, then drive aggressively to see if the code returns. If it sets again, review freeze frame data—this may reveal clues about when and under what conditions the misfire occurs.