What does it mean?
OBD II fault code P0314 is a generic code that is defined as “Single cylinder misfire -cylinder not specified”, and is set when the PCM (Powertrain Control Module) detects a misfire on a single cylinder that cannot be identified. Note that within the context of code P0314, the misfire can occur sporadically, intermittently, or, it can occur continuously.
Depending on the severity of the misfire, the PCM may either illuminate a warning light permanently, or cause a warning light to flash whenever the misfire occurs.
While modern automotive electronics have reached a high level of sophistication, and is generally capable of controlling/managing all aspects of an engines’ operation, and even have some “fuzzy logic” capabilities in the sense that PCM programming can adapt autonomously to accommodate different driving styles/conditions, it must be understood that modern engine and fuel management systems are also severely limited in some areas.
For example, all of the advanced capabilities of an engine/fuel management system depend on the engine being in good, if not perfect running condition if these management systems are to work as intended, but as with so many other things concerning automotive diagnostics, the devil lives in the details.
Let us briefly look at the details as they pertain to code P0314- The principal reason why modern engine and fuel management systems are as affective as they are is the fact that both the ignition and fuel delivery systems have self-diagnostic capabilities that use dedicated feedback circuits to confirm whether or not an event had actually taken place.
For instance, the ignition system includes circuits that confirm that a spark had been delivered to each spark plug at the proper time, while the fuel injection system includes dedicated circuits to confirm that the injectors had actually injected fuel into each cylinder, and that the injectors had done so at the correct moment.
If any of these circuits fail, or if something else happens that prevents sparks and fuel being delivered at the appropriate time, the PCM is made aware of that fact through dedicated feedback circuits and input data obtained from a variety of sensors. In this manner, the PCM is able to recognize that one or more cylinders are experiencing misfires, and it will set specific misfire codes that identify all the affected cylinders as a result.
However, the PCM is not able to monitor the mechanical condition of the engine directly; it can only infer that the engine is in good condition based on input data from sensors. These sensors include, but are not limited to, oxygen sensors, air/fuel ratio sensors, exhaust gas temperature sensors, NOx sensors, various engine and coolant/fluid temperature sensors, and others to a greater or lesser extent, depending on the application.
If the engine is in good mechanical condition and there are no fault codes present, all the input data the PCM (and other control modules) receive from all sensor will fall into acceptable and/or allowable ranges. As stated elsewhere, the PCM requires that the engine be in a good running condition for it to be able to manage the operation of the engine effectively, since it cannot control what it cannot monitor directly.
For instance, the PCM cannot monitor the compression in each cylinder directly, nor can it monitor the actual combustion temperature in each cylinder. Thus, should the PCM recognize, say, a sudden slight decrease in the exhaust temperature, or a sudden increase in the temperature of the catalytic converter(s), it will check for failures in all the relevant implicated sensors or circuits that could conceivably have caused the change in the exhaust gas or catalytic converter temperature.
NOTE: A decrease in exhaust gas temperature will result from one cylinder misfiring because the air/fuel mixture is not combusted, or combusted completely in that cylinder, thereby causing an overall drop in the exhaust gas temperature. An increase in the te