To keep the fuel pressure constant, the vehicles are equipped with a fuel pressure regulator.
There are vehicles that have a fuel pressure system that is integrated into the fuel rail assembly. There are also vehicles that have a fuel supply with no return. In the latter, the regulator is part of the fuel pump module inside the tank. It should be noted that, when the fuel supply is non-return, it is controlled by the PCM (Power Train Control Module), in addition, the fuel pump output and the fuel rail pressure is determined by the FRP sensor (Fuel Rail Pressure Sensor) who uses the fuel temperature to determine the fuel pressure.
When the DTC code P0089 OBD II is set, it means that the PCM (Powertrain Control Module) has concluded that the fuel pressure is not within the specifications already predetermined by the manufacturer.