The code is misleading, and is based on a standard set of definitions that are a one size fits all for a broad range of engines and vehicles. The low to which it refers has nothing to do with the true voltage to the lift pump, but is from the sensor in the injection system telling the system that the input fuel circuit feed pressure is insufficient. The same code is used in the gas engines, and there it means that the main in-tank fuel circuit pressure pump has failed.