ScanGauge II showing fuel used while engine stopped
 

I have a ScanGauge II in my 2017 Prius, and when the ICE is stopped, the GPH meter shows a constant 0.04. This results in my average steadily declining while stopped, which I imagine is going to make it a little difficult to dial in exact fuel economy using the fillup mechanism.

This is a new ScanGauge, with the latest firmware. (4.42)

Any ideas why this might be, and perhaps a way to correct it? (I don't see anything in the SG manual about correcting fuel used, only speed)

Not sure, is it set for hybrid mode? If not, try that first. This was a problem for some cars with older SG software. I had mine updated recently to the ecomodder 4.13EM version which was designed to correct just that problem. http://ecomodder.com/forum/showthrea...ade-35499.html
I had several conversations prior to upgrading with Joey Snyder from Linear Logic. I'd asked him at that time if the 4.13EM "fix" was included in later updates. He said it was not. If the hybrid mode doesn't help, I suggest you contact Joey and see what he suggests.

I just bought it, and it has the 4.42 firmware. I'll send Joey an e-mail and see what he suggests.

I did check the mode, and it was indeed set to gas, but setting it to hybrid made no difference, even after unplugging/replugging in the SG.

Remember that the ScanGauge only displays what the OBD 2 is telling it. What I am getting at is that the problem may be car related, not ScanGauge related, such as noise on an input sensor.