Most likely cause is an open circuit between the dash and the sending unit in the tank. Unlike all other manufacturers that read empty when there's a break in the circuit, GMs read full. If you can find the sending unit wire at the tank, unplug it and ground it to the body with a jumper wire. If the dash gauge reads "empty", the sending unit is defective. If the gauge stays on "full", there's a break in that wire or a loose pin on the gauge cluster.
February, 18, 2012 AT 12:59 AM
Youll need to remove the sending unit in the tank. Use a ohm meter to check the resitter on the unit.
February, 18, 2012 AT 1:03 AM
Thank you cadieman. Can that be done by a plug at the tank so he doesn't have to pull the sending unit out?
February, 18, 2012 AT 1:09 AM
Car hit it on the head you need to check the continuaity from the dash switch wire to the sending unit wire.
February, 18, 2012 AT 1:56 AM
He needs to check from the dash control wire to the sending unit connecter. If it shows open youll need to test the sending unit. Hook a wire to the dash switch then to the sending unit and see if it reads its the same color. You dont need to cut any wires. Wire crimper cut through the plastic wrapping on the wire. Then you can pull the wire open for hooking up a test wire. Simply remove the test wire and the plastic on the wire can simply be taped up. This is a open wire.