Component Functional Description-FPCM System

Powertrain Control Module:  The PCM monitors the input signal from the Fuel Rail Pressure Sensor to determine the commanded duty cycle to the FPCM. On a fixed pressure system the commanded duty cycle is varied to maintain a constant pressure of 400 kPa (58 psi). On a variable pressure system the commanded duty cycle is varied to adjust fuel pressure based on engine needs. The PCM will command the operation between 11% and 89% duty cycle. Ambient temperature and fuel temperature can also contribute to fuel pressure changes. The pressure is raised during high ambient temperatures to prevent boiling of the fuel.

Fuel Pump Control Module (FPCM):  The FPCM performs fault detection and reports faults to the PCM through the PWM Feedback circuit. The normal feedback circuit operating duty cycle range is between 3% and 97%. When the system is operating normally with no FPCM system faults, the duty cycle on the feedback circuit to the PCM is 50%. When the FPCM detects a fault it will send a duty cycle that aligns with the failure mode detected. If the duty cycle is 0% or 100% the PCM will set the Loss of Communication fault against the FPCM. Depending on the failure mode detected the PCM and FPCM can react by reducing the PWM output duty cycle or defaulting to an 80% duty cycle. This is explained further in the PCM/FPCM Reaction column of Failure Mode table below.

Fuel Pump:  The Fuel Pump operates in the same manner as a typical Brushed DC motor. The only difference is that the speed is reduced due to the PWM output voltage from the FPCM being less than 100%.

• Dual Pump Systems:  On vehicles with two Fuel Pumps, the pumps operate separately but are serviced as an assembly. During normal operation both Fuel Pumps are used to provide the system pressure and volume needed during most engine operating conditions. The exception is at idle, or idle and purging where there is extremely low fuel demand.  During this mode Fuel Pump 2 is typically turned off. When more fuel demand is needed (typically off idle) Fuel Pump 2 is turned on and both pumps are operated at the same duty cycle. If either pump is failing the vehicle may still operate normally during most driving conditions but would have performance issues under heavy engine load when both pumps are needed. If a failure is detected for either Fuel Pump or circuitry, the duty cycle will typically default to 80%. If Fuel Pump 1 (primary) is defaulted to 80%, Fuel Pump 2 may remain off during most operating conditions. However, if Fuel Pump 2 is defaulted to 80%, the primary pump will continue to operate at the lower duty cycle range. The reason for this is that the primary pump operates the jet pump to pull fuel from the secondary side of the Fuel Tank and also fills the Fuel Pump assembly reservoir.