Ok, my friends mother's car is throwing a Code 42 (fuel pump). How can I check the fuel pump...what does the code mean? Is the voltage getting to the FP not enough, or how does the ECU check the FP? Can I check the voltage or current in the wires or something, or does the FP have to come out to be checked?

I'm not sure what kind of car your mom drives, but I'd guess its the fuel pump relay that isn't working if its throwing a code. The ECU controls the relay rather than the pump itself in DSM's. Diagnostics can't be thrown by the fuel pump since its only power in and ground out, but a relay can throw short to ground, open-circuit, or short to battery diagnostics.