F 350 4WD Super Duty V10-6.8L (2002)
Fuel Pump Signal: Description and Operation
Fuel Pump Monitor
Applications Using a Fuel Pump Relay for Fuel Pump On/Off Control
The Fuel Pump Monitor (FPM) circuit is spliced into the Fuel Pump Power (FP PWR) circuit and is used by the PCM for diagnostic purposes.
The PCM sources a low current voltage down the FPM circuit. With the fuel pump off, this voltage is pulled low by the path to ground through the
fuel pump. With the fuel pump off and the FPM circuit low, the PCM can verify that the FPM circuit and the FP PWR circuit are complete from
the FPM splice through the fuel pump to ground. This also confirms that the FP PWR or FPM circuits are not shorted to power. With the fuel
pump on, voltage is now being supplied from the fuel pump relay to the FP PWR and FPM circuits. With the fuel pump on and the FPM circuit
high, the PCM can verify that the FP PWR circuit from the fuel pump relay to the FPM splice is complete. It can also verify that the fuel pump
relay contacts are closed and there is a B+ supply to the fuel pump relay
