What does it mean?
OBD II fault code P01C1 is a generic trouble code that is defined as, “Fuel Rail Pressure Sensor Circuit High Bank 2”, and is set when the PCM (Powertrain Control Module) detects an abnormally high electrical current or voltage in the control and/or signal circuit(s) of the fuel rail pressure on Bank 2. Note that “Bank “refers to the bank of cylinders in V-type engines that does not contain cylinder #1.
All fuel-injected engines, regardless of their make, model, or type can only function properly when the fuel they run on is available within a narrow range of pressures. This is to allow the fuel injectors to not only inject the required volume of fuel during each injection event but also to atomize the fuel properly during injection events to ensure the efficient combustion of the fuel.
Thus, if the fuel pressure is too low, the injectors may not inject fuel at all, while if the fuel pressure is too high, the injectors may inject too much fuel, and may also not vaporize the fuel to the required degree to ensure proper combustion of the air/fuel mixture. Moreover, fuel delivery systems are specifically designed to meet the fuel demands of each engine design.
As a result, parameters such as the capacity of the fuel pump, the flow rate of fuel through the system at all engine speeds, the pressure required to atomize the fuel, and the injection capacity of the injectors on each engine design or type is specific to that particular engine design or type. All of the above requirements would be impossible to achieve and maintain unless the PCM (and other control modules) had a way of monitoring the fuel pressure in the fuel rails continuously.
Therefore, to do this, all engines are fitted with dedicated fuel rail pressure sensors to monitor the pressure in the fuel rails for as long as the engine is in operation. In a fully functional fuel delivery system, the PCM matches the fuel supply to constantly changing fuel demands either by varying the speed of the fuel pump or by activating a pressure relief valve in the fuel system to vent excess fuel pressure back to the fuel tank via one or more dedicated return lines.
Regardless of the method employed by any given PCM, all PCMs are programmed to maintain the fuel pressure within a very narrow range on either side of a desired or specified pressure at any given engine speed and load to ensure proper engine operation under all operating and driving conditions.
Thus, if a failure, malfunction, or defect occurs in the fuel system that prevents the PCM from monitoring or managing the fuel pressure in the fuel rails, it will recognize that it cannot control the fuel pressure effectively, and it will set code P01C1, and illuminate a warning light as a result.
Note though that apart from the above, the PCM may also set additional trouble codes, initiate a fail-safe or limp mode, or revert to a default fueling strategy that may or may not include restricting the engine speed, depending on both the application and/or the nature of the problem.