Scanguage is not accurate.

When I am coasting downhills, my scanguage will sometimes get stuck on 99999 Instantenous MPG. Yesssssssss!!!! It artificially inflates Tank MPG and Trip MPG.

Like everyone else said, the only way to get a true MPG is to divide Miles / Gas Filled at the pump.

 

You don't understand how it works. It is absolutely accurate.

It reads OBD II codes and live data, and does very simple addition, multiplication, or division. On the D2, as well as many other vehicles, the injectors shut off when the TPS is at full closed under normal conditions. This sets the fuel consumption live data to 0, which the scangauge then displays "instant" MPG as 9999 MPG (using current fuel consumption divided by current speed), as it is not possible to divide by 0.

There are instructions in the manual that came with the gauge to change this behaviour.

Don't blame the tool. Tools are useless unless you know how to use them.

 

My wifes Volvo has a trip computer with instant MPG, I like to shift into neutral and coast down really long hills and see how long I can keep the MPG pegged at 99.9.