Lifetime average on my 07 edge is currently 18. Maybe 22 highway, 23 sometimes. Not as high as I thought it might be when we bought it, but gas is cheap yet. Owned 3 years, at around 45000 miles.
Just bought a code reader from Walmart, 40 dollar cheapo. Worked fine. I have no codes on the edge, but my F150 acts up about every six months, so I am ready this time. You do need the ignition in the on, ready to start position. Maybe that was not the issue.