What does it mean?
OBD II fault code P00C6 is a generic trouble code that is defined as, “Fuel Rail Pressure (FRP) – Engine Cranking – Pressure Too Low” or sometimes, as “Fuel Rail Pressure Low During Cranking”, and is set when the PCM (Powertrain Control Module) detects a condition in which the fuel pressure in a fuel rail is too low to- allow the fuel injectors to open to cause the fuel to be properly atomized during injection In both conditions, the PCM will not complete the starting circuits during cranking, effectively preventing the engine from starting.
While modern fuel injection systems have made cars more fuel-efficient than they have ever been, the biggest drawback all fuel injection systems have is that the fuel pressure must be maintained within a very narrow band on either side of an ideal pressure for the fuel injectors to work as intended.
In older fuel injection systems, the fuel pressure was supplied by a fuel pump in the fuel tank that delivered fuel to the fuel rail and from there to the injectors, at a near-constant rate and pressure.
In practice, both the volume and pressure of the supplied fuel were somewhat higher than the engine needed even under wide-open throttle conditions, so to manage the fuel pressure when the demand for fuel suddenly decreased, fuel rails were typically fitted with pressure relief valves that vented excess pressure back to the fuel tank through dedicated return lines.
We need not delve into the details of the various mechanisms that controlled these pressure relief valves but suffice it to say that in a fully functional fuel system, the pressure relief valves could control the fuel pressure to within one or two percent of the ideal fuel pressure under all operating conditions. In modern sequential fuel injection systems, however, the fuel pressure is primarily regulated by the fuel pump.
To achieve this, the PCM or dedicated fuel control module varies the speed of the fuel pump to adapt the fuel pressure to suit the current fuel demand. In practice, the implicated control module increases the speed of the fuel pump under high-demand conditions to increase the volume of fuel, as well as its pressure.
When the demand for fuel drops as the engine speed decreases, the implicated control module reduces the speed of the fuel pump, thus reducing both the volume and pressure of the fuel delivered to the injectors to suit the changing operating conditions.
Since the fuel pump regulates the fuel pressure on sequential injection systems, these systems have neither fuel regulators nor return lines, since the fuel pressure is always maintained within a very band on either side of the ideal pressure by the speed of the fuel pump.
Therefore, the actual fuel pressure plays a critical role in efficient engine operation, but the actual fuel pressure available to the injectors plays an equally critical role in the highly complex series of events that must all occur in a fixed order before a modern engine will start. The process of starting a modern engine is a highly complex and technical one, and as such, the complete process falls outside the scope of this article.
However, we can break a generic process down into bullet points to make at least a small part of the process clearer- Assuming that all security passcodes are recognized and verified by several control modules, the PCM activates a part of the starting circuits One function of this part of the starting circuit is to activate the fuel pump for a second or two to verify that the pump works and that there is fuel in the tank If the fuel pump works and delivers pressurized fuel to the fuel system, the PCM and other control modules will verify that the static pressure falls within a specified, and extremely narrow range of pressures If the fuel pressure is within the specified range, the PCM will allow the engine to crank, during which time it records the cranking speed and dozens of other parameters, During this time the PCM also determines the position of p