Theory Of Operation

GENERAL OPERATION:  When the Powertrain Control Module (PCM) receives a 'Start' or 'Run' signal, it energizes the Fuel Pump Relay which sends a continuous 12.0 volt supply to the Fuel Pump Control Module (FPCM). Depending on vehicle configuration, the Fuel Pump Relay can be either a removable component or part of the Printed Circuit Board (PCB) inside the Power Distribution Center (PDC). The PCM sends commands to the FPCM through a Pulse Width Modulated (PWM) control signal. The FPCM in turn regulates the PWM voltage output to the Fuel Pump Assembly based on inputs from the Fuel Pressure Sensor and other engine demands. The PWM signal will vary from 10-100% to maintain the proper fuel pressure in the system. This is a Constant Pressure Fuel system which means any fuel pressure test performed on the Fuel Pump should show a continuous pressure (regardless of the changes in PWM).

DIAGNOSTICS:  The PCM directly monitors the Fuel Pump Relay Control circuit and the Fuel Pressure Sensor for circuit faults. The PCM also monitors the feedback from the FP Sensor to determine if the Fuel Pump Assembly is able to achieve and maintain the desired pressure in the fuel system. The FPCM is a smart device which monitors the Fuel Pump Assembly wiring for circuit faults and reports the faults to the PCM. The PCM receives the feedback from the FPCM through the PWM feedback signal. These faults reported will be stored in the PCM. The pump motor is also monitored for mechanical and performance issues such as Fuel Pump Motor over temperature, blocked pump rotor, dry run, and pump motor speed deviation. If any of these conditions are present, the FPCM will default the duty cycle for the Fuel Pump Assembly to (80%) to maintain fuel pressure. The default duty cycle could cause the fuel system pressure to be higher than calibrated threshold, which can also cause the P062A-Fuel Pump Control Performance fault to set. If other FPCM DTCs are present along with the P062A they should always be diagnosed first.