Functional Description - Fuel Pump Control Module (FPCM)

WARNING: This page is about a different car, the 2023 Jeep Grand Wagoneer L and 2023 Jeep Grand Wagoneer. 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 12.0 volt supply to the Fuel Pump Control Module (FPCM). Depending on vehicle configuration, the Fuel Pump Relay can be either a removable component or be part of the Printed Circuit Board inside the Power Distribution Center (PDC) and not separately replaceable. The FPCM grounds through a chassis ground. The fuel pump grounds through the FPCM using the same chassis ground.

To maintain the desired fuel pressure, the PCM sends a PWM duty cycle signal to the FPCM. If there are no system faults present, the Fuel Pump Control output to the Fuel Pump is based on the duty cycle sent by the PCM. The graph below shows the FPCM output to the Fuel Pump in proportion to the PCM command signal. The FPCM output to the fuel pump will not read as a duty cycle when monitoring with a Mopar Scope. It will be a consistent voltage output that is a percentage of battery voltage.

Courtesy of CHRYSLER GROUP, LLC

The FPCM performs fault detection and reports faults to the PCM through the PWM Feedback circuit. The feedback circuit can be monitored using the Mopar Scope and functions as follows:

The feedback circuit is a 5.0 volt duty cycle.
The PCM supplies the 5.0 volts for the feedback circuit.
The FPCM pulses the low side of the circuit to communicate with the PCM.
The normal duty cycle operating range is between 3% and 97%.
When the system is operating normally, the FPCM will send a 50% duty cycle on the feedback circuit to the PCM.
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.

NOTE:

Monitoring the FPCM internal driver with an open feedback circuit using the Mopar Scope will show a pulse width signal with a very low voltage (.025v - 0.5v). This is picking up voltage from the internal driver device that is still trying to pulse the duty cycle to the PCM. This can be useful when performing diagnostics on the feedback circuitry.

Depending on the failure mode detected by the PCM and FPCM, the FPCM can react by either reducing the PWM output duty cycle, or defaulting to an 80% duty cycle for the fuel pump operation.