P0302 and P0300 Fault Codes on 2006 Dodge Charger 3.5L - Diagnosis and Solutions
At 284,000 kilometers, the vehicle exhibits P0302 and P0300 diagnostic trouble codes despite having fresh spark plugs and good compression readings. Coil pack replacements have been performed, but the P0302 code persists. The engine stumbles slightly during startup and when accelerating beyond 80 km/h on highways, then stabilizes. Occasional dashboard power loss has also been observed, though the vehicle never completely stalls. No other codes are present. The issue appears to be worsening over time. Given that spark plugs and compression are normal, potential root causes may include excessive carbon buildup in the combustion chambers or exhaust valve springs. A technical service bulletin (TSB) exists for certain vehicles indicating that carbon accumulation can lead to lean mixtures, resulting in misfires, hesitation, and stumbles—symptoms consistent with this case. While a static compression test shows normal readings, dynamic analysis using modern tools such as pressure transducers connected to a lab scope could provide deeper insights into intake, compression, power, and exhaust performance. Fuel trims and misfire counters on an OBD2 scan tool would also offer valuable diagnostic data. As a temporary measure, using a fuel system cleaner like Techron or a vacuum-based decarbonizer (e.g., OTC decarbonizer) may help reduce carbon deposits in valves and intake components. Additionally, replacing exhaust valve springs—known to degrade over time—is recommended per the TSB. This could improve engine performance and reduce misfire occurrences. Note: The intermittent dashboard power loss appears distinct from the engine misfire issue and may warrant separate investigation.
There is a known technical service bulletin (TSB) for certain vehicles related to excessive carbon buildup in the combustion chambers. This can lead to lean fuel conditions, resulting in misfires, hesitation, and stumbles—symptoms matching this issue. The TSB recommends decarbonizing the engine and replacing exhaust valve springs if they are weak. While a static compression test may show normal readings, actual performance under load could be compromised by carbon deposits that absorb fuel. Modern diagnostic tools such as pressure transducers connected to an oscilloscope can monitor intake, compression, power, and exhaust dynamics in real time—offering more detailed insights than traditional tests. A fuel system cleaner like Techron or a vacuum-based decarbonizer (e.g., OTC) may help reduce carbon buildup on valves and intake components. Misfire counters and fuel trims from an OBD2 scan tool would provide critical data for diagnosing the root cause. The intermittent dashboard power loss appears to be a separate issue and should be investigated independently.