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OBD II fault code P0300 is a generic code that is defined as “ Random/Multiple Cylinder Misfire Detected”, and is set when the PCM (Powertrain Control Module) detects either randomly misfiring cylinders, or misfires on multiple cylinders. All modern applications employ highly sophisticated circuits whose sole purpose is to detect misfires.
In fully functional systems, the misfire detection system uses input data that is delivered to the PCM via dedicated feedback circuits that let the PCM “know” whether or not a particular component such as spark plug or fuel injector had not only received a triggering signal, but also if the sparkplug or fuel injector had reacted to that triggering signal. If the PCM does not receive a feedback signal, it interprets the lack of that signal as a misfire.
However, some conditions, such as low fuel pressure or engine vacuum leaks can cause random misfires without the feedback signal from injectors and/or sparkplugs necessarily being affected, but in these cases, the underlying cause of the misfires will be indicated by dedicated fuel system and other codes that will be stored alongside P0300. Non-professional mechanics should therefore note that while P0300 is a generic code, the actual root cause(s) of the code is often make-and-model specific.
Nonetheless, while P0300 refers to faults in the ignition system, misfires, and especially random misfires, are often caused by faults that may not be directly related to the ignition system. Note that if the fault does involve the ignition system, the resulting code(s) will end in digits other than” 0”. For instance, if the misfire occurs on cylinder #4, the code indicating this will be P0304, where the “4” relates directly to the affected cylinder.
Similarly, misfires that occur repeatedly on specific cylinders will set codes that end with the numbers of the misfiring cylinders as the last digit in the codes.