I was using the GPS program on my cell phone. My battery was low, so I turned the GPS off but noted the remaining distance. I used my Altima's odometer, but after sometime I noticed that it hadn't changed very much (only 0.2 miles). I turned the GPS back on and discovered that I had actually driven about 6 miles. I am not sure what is wrong. Let me know your thoughts.

Start by disconnecting the battery for longer than 2 minutes, then reconnecting the battery terminals. If this doesn't correct the issue, refer to your owner's manual and remove the fuse that controls your electrics/dash guages. When you remove this fuse, your dash should die completely - no lights or gauge motion. Then put this fuse back in.

If neither of these help toward recalibrating your odometer, I'd contact Nissan b/c your overall mileage may be affected (if you aren't already referring to the total miles on your car).