Theory Of Operation

WARNING: This page is about a different car, the 2015 RAM 1500. However, it is still accessible from the selected car via links, so may be relevant.

When the Powertrain Control Module (PCM) receives a 'Start' or 'Run' signal, it energizes the Fuel Pump relay which sends a continuous 12 volt supply to the Fuel Pump Control Module (FPCM). The PCM also sends a Pulse Width Modulated (PWM) control signal directly to the FPCM which regulates the PWM voltage that will be sent to the Fuel Pump Module. The PWM will vary from 10-100% depending on the input of the Fuel Rail Pressure Sensor and other engine demands. The PCM receives a PWM signal from the FPCM representing the state of all inputs and outputs of the FPCM. This is a Constant Pressure Fuel system which means any pressure test performed on the Fuel Pump would show a continuous pressure (regardless of the changes in PWM). If a pressure sensor fails or other failures are present; The duty cycle goes to a default setting (100%) to maintain fuel pressure.