Frequently Asked Questions: (1.)What are the symptoms of a bad fuel pump sending unit? A fuel gauge that reads full or empty all the time, or has a needle that moves erratically. (2.)How does a fuel sender work? Fuel senders have a rheostat that provides a resistance to ground. As the fuel arm moves from the empty to the full position a contact is moved across the board on the rheostat which varies the resistance seen by the fuel gauge. (3.)What causes a fuel sending unit to go bad? .
