The 2003 Altima fuel pump is beneath the back window. There are two locking mechanisms under the front of the seat to gain entry. Pull the two lock rings to the front of the car to free the seat from the door. Remove the bottom seat cushion that gives you access to the cover plate of the fuel pump. The plate is on the driver's side and it's flat. There are four 1/4 turn plastic phillip head locks on the cover. Remove the 4 keys, raise the cover and disconnect the electrical connection from the pump. Disconnect the fuel line that will have the residual pressure in the tank. Squeeze the connector lock that is normally white or black, and pull the fuel line to the front of the car with a twisting motion. Oil is flowing out, so have something under the vehicle or fuel line to capture or remove the fuel. The pump is protected by a threaded black ring in the tank. Remove the ring by turning it clockwise until it is removed. Then take the fuel pump halfway up. There is now some interference from the two wires attached to the bottom of the pump and the fuel gauge sending the float unit. You will have to tilt the pump and maneuver it until you clear the float and wiring. Cautions: No smoking, do not bend or distort the sending unit float arm, the fuel line is under pressure, note the location of the pump assembly O ring seal, assembly is the reverse of disassembly, and the entire assembly is replaced, and not just the pump like other vehicles. The pump assembly has the filter/sock incorporated with the unit, and it is the only filter in the entire fuel system.[br]
[br]
For more information you can visit Car manual’s [https://blog.carmanuals.org/|Auto Blogs]
[br]