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Just got a 98 Trans am and fuel gauge doesn't work. When car is off, it reads at 1/4 tank. When car is on it just stays on empty. Would this be a sending unit issue or possibly something else?
There's a plug in front of the driver side rear wheel where the wires for the pump go through. You should be able to unplug that and short the gauge wire (purple if I remember) and un short to see if the gauge moves. Double check on wiring diagram though.
I found it - circuit 30. shorting and open should flip between empty and full.
Last edited by JoshHefnerX; Jun 2, 2021 at 10:01 PM.
Short it to ground - body structure. That side of the circuit measures resistance across it and it uses a ground side to do it. So if you short it to ground - you'll get 0 resistance, leaving it open is infinite resistance. You should be able to have a helper let you know if the gauge is bouncing when you do that (key on, engine off). if so, the problem lies between there and the sender. If not, the problem lies between that plug and the pcm.
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Fuel gauge issue 
