Join Date: Mar 2010
Location: Ventura County, CA.
I'm pretty sure it keeps track of MPG continually. I don't think it phases out old data. When you reset it, is when it starts over. If you reset it and drove around an averaged 30.4 mpg, and then just let the car sit and idle, your average MPG will continue to keep track and get lower as it sits and burns fuel...
2009 Imperial Blue Metallic Cobalt SS/TC Sedan - "Stock":
2008 Victory Red HHR SS - Stock
2005 Chili Pepper Red Ion Redline - Stock
2007 Sunburst Orange Metallic LS Coupe - Sold