Theory Of Operation

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 Smart Fuel Pump Control Module (FPCM). The PCM also communicates with the FPCM through a Pulse Width Modulated (PWM) Fuel Pump PWM Control signal. The PCM commands the speed of the Three Phase Fuel Pump based on the input from the Low Fuel Pressure Sensor and other engine demands. The purpose of the system is to maintain the target fuel flow supply to the High Pressure Fuel Pump for all engine operating conditions.

The PCM performs fault detection on the Fuel Pump Relay Control circuit and Fuel Pump PWM Control circuit. The FPCM monitors the power supply circuit and Fuel Pump circuits for faults as well as the Fuel Pump for over current, over temperature and other performance issues and communicates the faults back to the PCM through the PWM command signal. All of the low pressure fuel system faults are reported in one of the following fault codes:

• The P0627 Open Circuit fault will set for an open or voltage high on the relay control circuit, an open on the voltage supply or Fuel Pump PWM Control circuit, or if there are any wiring issues (opens, short to ground or voltage) on the Low Pressure Fuel Pump circuitry. The relay control faults are monitored when the Fuel Pump is commanded off and the other faults are monitored when the Fuel Pump is commanded on.
• The P0628 Circuit Low fault will set if the relay control circuit or Fuel Pump PWM Control circuit are shorted to ground when the Fuel Pump is commanded on.
• The P0629 Circuit High fault will set if the IN Bus command signal circuit is shorted to voltage when the Fuel Pump is commanded on.
• The P062A Performance fault is designed to detect Fuel Pump PWM Control signal frequency out of range as well as FPCM and Fuel Pump issues such as over current, over temperature, blocked pump and internal control module issues when the Fuel Pump is commanded on.