Eliminating the possibility that the average speed indicator in my Kiz is influenced by a GPS signal was the point of my stating I don't have the built-in navigation unit. If the GPS I used were slaved to the odometer in some way it would certainly be suspect. I found the output from the console mat...

No, I don't have the built-in navigation unit. I used a Garmin mounted on my dash.

An informal road test I performed:

GPS unit that shows MPH - shows 72mph
Kiz dash "avg speed" reset during level interstate travel at 75mph by the speedometer - shows 72mph

Tests at lower speeds showed the discrepancies didn't start appearing until speeds over 45mph.

I have had this issue as well with my iPod nano. The user manual for the car (2010) does say to disconnect USB-operated devices before turning off the engine, I never do. There's a window in time after turning off the car where I can turn it right back on again and be fine, or come back in a longer ...