BMW X5 Fuel Pump Replacement /Fuel Level Sensor 2000-2006 E53 ↗
Swapping the E53 fuel pump and the left-side fuel level sensor from under the rear seat (the sensor cover is held by four 10 mm nuts). The site rates it a home-mechanic job of under an hour and recommends replacing both units and the filter together.
Tools mentioned: 10 mm socket, fuel pump lock-ring spanner