1) Turn on car and set sound source to AM/FM radio.
2) Push in the volume (power) and tune (audio) knobs at the same time
3) You should now see a "failure analysis" screen on the nav
4) Type in the two-digit code "39" and hit enter
5) The nav will ask you if you want to reset the code. Hit enter to confirm.
6) Finally push the volume (power) knob to return to the map.