Try to locate one before attempting a complex repair. To diagnose fuel pump circuits there's no replacement for a good wiring diagram.

NOTE: If no drivability complaints are present and P0231 code is stored, suspect open in feedback circuit between splice and PCM Possible Solutions Fuel pump fuse blown due to short to ground.Harness chafing causing open in fuel pump supply circuit.Potential causes of a P0231 code include: If it sees voltage that is too low or no voltage at all, it may set P0231. As it activates the fuel pump relay, it expects to see battery voltage on the feedback circuit. The PCM monitors this feedback circuit to ensure that there is proper voltage being sent to the fuel pump. The splice is usually located close to the PCM. This is simply a circuit spliced into the voltage feed to the fuel pump. Some vehicles have a feedback on the fuel pump supply circuit. When the PCM (powertrain control module) activates the fuel pump relay, voltage is supplied to the fuel pump and it pressurizes the fuel system. The fuel pump is powered by the fuel pump relay. Although generic, the specific repair steps may vary depending on make/model. This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles. Fuel Pump Secondary (Feedback) Circuit Low Voltage What does that mean?

2005 expedition fuel pump relay problem