The Code Reader takes common DTCs, breaks down when and why they occur and looks at symptoms and causes to help listeners make an accurate diagnosis.
P0300 sets when the control unit recognizes that one or more of the cylinders is not contributing, or working as hard as the others. Now P0300 being “Random” misfire, means that the control unit has not been able to pinpoint the exact cylinder or cylinders that is causing the problem, and if this is the only code this is also a general indication that the problem is intermittent. But I also want to throw in that on the topic of misfire codes and their diagnosis, I’ll refer to them as P030x, meaning that if the last number is anything other than 0, it indicates that the control unit has been able to identify a specific cylinder, for example if the code is P0303, it would mean that the control unit has identified cylinder number 3 with a misfire condition.
The majority of the time, misfire detection is based upon the crankshaft rotational velocity that is detected by the crankshaft position sensor. A misfire causes the crankshaft to slow down, and when the PCM recognizes this to be happening above an allowable threshold, it can set a misfire code.