|Trouble Code||Fault Location||Probable Cause|
|P0300||Random/multiple cylinder(s) -misfire detected||Spark plug(s), HT lead(s), injector(s), ignition coil(s), low compression, wirin|
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What Does Code P0300 Mean?
OBD II fault code P0300 is a generic code that is defined as “Cylinder Misfire Detected Random Cylinders”, and is set when the PCM (Powertrain Control Module) detects either a random misfire on one cylinder, or multiple cylinders that misfire randomly. Note that in this context, “random” refers to misfires that do not occur in a fixed pattern that corresponds to engine speed.
On most applications, the PCM uses the Crankshaft Position Sensor to both generate the ignition sparks, and to serve as a device to monitor the crankshaft’s rotational speed for the purpose of misfire detection.
On a fully functional engine on which there are no misfires present, the crankshaft rotates at a steady rate, since all the cylinders contribute equally to the crankshafts’ rotation. However, a cylinder that misfires does not contribute an equal share of energy, which causes the crankshaft’s rotational speed to fluctuate slightly. If one or more cylinders misfire regularly, the PCM can determine which cylinders are affected by using complex algorithms that in their turn use a reference point on the crankshaft position sensors’ reluctor ring to identify the misfiring cylinder(s).
However, in the case of misfires that occur randomly, the PCM is not able to identify the affected cylinder(s), and in these cases, the PCM will set code P0300 to indicate that randomly occurring misfires are present. Note that on most applications, misfire related codes will be set when the crankshafts’ rotational speed varies by more than about 2 percent within a predetermined time period, which varies somewhat between applications.
Why does code P0300 affect Nissan applications more than others?
Although code P0300 can affect any vehicle, many Nissan applications are extremely susceptible to this code and for reasons that are not always obvious or apparent. However, long experience in the auto repair industry has taught that most Nissan applications are extremely sensitive to aftermarket ignition system components, including spark plugs, ignition coils, and both crankshaft and camshaft position sensors. In addition, one particular Nissan engine, the KA24DE engine found in older Nissan applications, was particularly susceptible to vacuum leaks caused by a poorly designed intake manifold that caused the intake manifold gaskets to leak, thus causing random misfires.
Where is the P0300 sensor located?
The image above shows the typical location of the ignition coils on a 4-cyl Nissan engine, ignition coil failure being a common cause of code P0300 on a large number of Nissan applications.
NOTE: Due to the large number of possible causes of code P0300 many Nisan applications, it is not possible to provide accurate information on the locations of all part/components that can fail on all applications. Therefore, it is important to refer to the manual for the affected application for details on the exact location of all implicated part/components. Failure to locate and identify parts correctly could result in misdiagnoses and the unnecessary replacement of parts and components.
What are the common causes of code P0300?
While most Nissan applications do not tolerate aftermarket ignition system components well, there are several other causes of code P0300 that are more common on Nissan applications than on almost any other, these causes being-
- Defective PCV (Positive Crankcase Ventilation) valves and/or PCV valve hoses that cause engine vacuum leaks
- Marginally worn spark plugs, or the use of spark plugs that are not recommended by Nissan
- Defective ignition coils, or defective ignition coil drivers in the PCM
- Insufficient fuel pressure
- Poor electrical contacts in fuel injector wiring
- Insufficient compression caused by the ingestion of foreign objects, most notably the retaining screws from intake manifold runner flaps that work themselves loose, and end up being sucked into a cylinder
- Defective variable valve timing control solenoids that can cause too much valve overlap, thus causing random misfires
- Insufficient oil pressure, which causes VVT control solenoids to malfunction
- Defective upstream air/fuel ratio sensors
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