What does it mean?
OBD II fault code P0313 is a generic code that is defined as “Misfire detected -low fuel level”, and is most commonly set when the PCM (Powertrain Control Module) detects a misfire on one or more cylinders when the fuel level in the tank is below a minimum allowable level.
If this code sets when the fuel level is low, it is typically because the fuel level is so low that the pickup point on the fuel pump is sometimes above the fuel level, which causes the fuel pump to “suck” air, which in turn, causes intermittent failures in the fuel supply to the injectors.
Note also that if code P0313 sets under low fuel conditions, it will only be after the engine has completed at least six full revolutions after starting, and then only if the PCM has determined that the fuel level is below a predefined critical level. However, code P0313 is among a group of ambiguous codes, which if taken at face value, appear to be easily resolvable, but in practice though, code P0313 can also be set even if the fuel tank is full.
Thus, if it is certain that the fuel level is above the fuel pump pickup point, it is often more profitable to approach this code from the standpoint of there sometimes not being enough fuel (relative to air) available at one or more cylinders to complete the combustion process successfully.
An air/fuel imbalance is most commonly due to large vacuum leaks that cause unmetered air to enter the engine, defective fuel injectors, and/or defective sensors that could include the MAF (Mass Airflow) sensor, IAT (Intake Air Temperature) sensor, and MAP (Manifold Absolute Pressure) sensor, among others.
An alternative approach might be to look for problems that prevent combustion on one or more cylinders altogether: in the latter case, the problem could be electrical, such as the absence of a spark, or mechanical, such as a partial or complete loss of compression on one or more cylinders. In practical terms, the resolution of this code often depends on whether or not other codes are present along with P0313.
More importantly, though, if other codes are present, the repair steps required to resolve all codes depend entirely on which additional codes are present along with P0313. For example, if the fuel level is known not to be low but there are codes present (along with P0313) that relate to low fuel pressure, the fault clearly involves faults with the fuel system, as opposed to a low fuel level in the tank.
From the above it should be clear that code P0313 could have many possible causes besides a low fuel level. However, most, if not all other possible causes will almost certainly be indicated by trouble codes that relate to specific issues other than a low fuel level. In these cases, it is almost certain that P0313 had set as a reaction to other issues, as opposed to P0313 having been the cause of the additional codes.
Note that if other codes are indeed present along with P0313, one or more of these codes could cause the PCM to initiate a failsafe or limp mode, particularly if there is a possibility that the misfire might damage the catalytic converter(s).