2004 Honda Odyssey P0301 P0304 P0306 P0300 P1399 - Misfire Codes and Check Engine Light Issues
I own a 2004 Honda Odyssey and recently experienced a serious issue. Two days ago, while driving on the highway, the check engine light and TCS warning light came on simultaneously. The vehicle began running roughly with an unstable idle. Upon inspection at AutoZone, I retrieved the following diagnostic trouble codes: P0301, P0304, P0306, P0300, and P139
Misfire codes such as P0301, P0304, P0306, and P0300 indicate cylinder misfires. The flashing check engine light suggests a potential catalytic converter failure if not addressed promptly. I assume you do not have access to a scanner capable of live data, including oxygen sensor voltage readings. Therefore, I recommend checking fuel pressure with the key off (KOEO) and monitoring for any drop in pressure. A significant pressure drop may point to an overfueling condition, which is common when misfires occur due to flashing CELs. Additionally, inspect the spark plugs for signs of wetness or black soot—this can indicate excessive fuel delivery.