FPCM System Description And Operation
SYSTEM DESCRIPTION: When the Powertrain Control Module (PCM) requires Fuel Pump operation it energizes the Fuel Pump Relay. The Battery voltage output from the relay does not connect directly to the Fuel Pump like traditional systems. Instead, the Battery voltage is supplied to the Fuel Pump Control Module (FPCM). When the ignition is switched on, the Battery voltage is present for approximately five seconds. Battery voltage should always be present during cranking or when the engine is running. The purpose of FPCM is to operate the Fuel Pump using a Pulse Width Modulated (PWM) output to reduce electrical load on the system. Most vehicle/engine combinations operate as a fixed pressure system . Vehicles with the 6.2L engine operate as a variable pressure system . It is necessary on some vehicles with the 6.2L engine to have a second Fuel Pump and FPCM to meet engine needs. The second FPCM performs the same diagnostics as the primary module but uses different DTCs.
SYSTEM OPERATION: 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 PWM 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.