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Discussion Starter #1

I have a question regarding EVAP diagnostics and the fuel sending unit in my 06 9-3SS 2.0T. Backstory is my gauge always reads empty and so I was diagnosing my sending unit and gauge using a resistor. The resistor indicated the gauge works (and the sender was open circuit) but when I started the car after a few seconds the gauge dropped to 0 and the fuel reserve light came on even w/ the resistor.

I'm going to replace the sending unit but this result got me thinking as to why the gauge dropped to 0 w/ the resistor+starting the car? I don't think anything shorted out. The resistor is rated for 7W which should be more than enough. Besides if I turn the ignition to lock when the gauge goes to 0, then back to on the gauge reads the level I would expect for that resistor again.

So something else is doing it and all I can think of is some kind of diagnostic that the EVAP system is running, realizing a mismatch from say the EVAP pressure sensor and puking? I'm not sure of my current fuel level right now (maybe 1/2 tank) but my resistor is 100 ohms or 1/4 tank. If the tank is filled above a certain level (say 75%) would such a diagnostic not run? I haven't seen anything in the WIS about such a procedure. I guess I could always check by filling my tank and dropping in a larger resistor.

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