The CCM (Component Comprehensive Monitor) monitors the sensor circuit to the PCM (Powertrain Control Module). In case the voltage is not within the calibrated levels, the test fails.
The Fuel Rail Pressure Sensor (FRP) measures the fuel pressure near the fuel injectors and sends a signal to the PCM (Powertrain Control Module) that uses this information to adjust the fuel injector in the pulse width and this way measure the fuel in each cylinder
The FRP (Fuel Rail Pressure) sensor varies its resistance taking into account changes in pressure, if the pressure drops, the electrical resistance decreases, and if the pressure rises, the resistance increases. Due to changes in the resistance the voltage drop at the sensor terminals is affected, therefore, it sends an electrical signal to the Power Train Control Module (PCM), which corresponds to the pressure. This sensor is considered passive, since it is connected to the circuit so that the variation of the resistance causes a variation in the total current flow.