The diagnostic code P2509 OBDII means that an intermittent power input signal has been detected in the Engine Control Module (ECM)/Powertrain Control Module (PCM). The signal is not continuous, and it is not within the parameters set by the manufacturer.
A contact relay supplies voltage to the ECM / PCM. The battery voltage, ground, and ignition circuits are located in this relay. In addition to these three circuits, the computer receives information via an output signal. If one of these signals is not within the established range, this code will be set.