The Powertrain Control Module (PCM) electronically controls the fuel pressure regulator via sensor signals. To accomplish this task, the control module makes some adjustments to the battery voltage and ground signal of the regulator while the vehicle is running. Thus, it activates a servomotor that triggers a valve that drives the required fuel pressure. The valve opens as the servomotor voltage increases, which is a step up in pressure.
The diagnostic code P228C OBDII is a code that basically signals the detection of a malfunction in the fuel pressure regulator 1. In this case, the code shows that the voltage in the regulator circuit is excessively below the allowable voltage. Consult the vehicle information source for the application for regulator number 1.