Storing the DTC P0148 OBDII code next to the Check Engine light means that the PCM (Powertrain Control Module) has detected a problem in the high-pressure fuel delivery system of a diesel engine.
The diesel fuel supply pump has a high pressure, which is necessary for the direct injection system. The PCM electronically controls the FCA (Fuel Control Actuator), which regulates the fuel pressure in the high-pressure chambers of the engine. Besides, there is a sensor that allows the PCM to monitor fuel pressure during the engine operation.