Because your odometer, or something connecting the odometer to the battery, is broken. Most likely the odometer is the problem if the rest of your dashboard is working fine.
By changing it to miles!
probably anti theft - need code to reset
It depends on whether or not the car has a digital readout. If it has a digital display, chances are it would be a wiring problem, somewhere right behind the odometer. If it has an analog display, since the spedometer still works, chances are the odometer itself (the display) has gone bad--like a little gear in there or something. This is one of the simplest odometer problems to fix; just replace the display piece. If the spedometer wasn't working it would be a whole different story--probably a faulty cable.
Put the key into the ignition and press the odometer button. While holding down the odometer button, turn the key to the on position. You will see "-----"on the odometer display. It will count down "-----" "----" "---" "- -" "-". Then you will see zeros on the odometer display "000000". You can now release the odometer button. This will reset the maintenance light on your dash!!!!!!
All newer vehicles have a combination electronic odometer/tripmeter - Odometer measures the total miles on the vehicle and the tripmeter measures the miles since the last time it was reset - used for logging trip distance, measuring mileage since last fuel stop to check mpg, and etc... There is a push button there somewhere on/at the dash that toggles the display between odometer/tripmeter - changing to the tripmeter display, and holding the pushbutton down will reset the tripmeter to O miles...
Might be a defective voltage regulator (not opening on engine shutdown)
The odo doesn't display speed at all, only distances covered.
I inquired about the conversion of miles to KM on my 2008 G35 and was told it was not a programmable option. The dealer offered to do it for $1800 as it required changing out the entire display module.
Celsius
It depends why it's changing. Windows default settings dims the display if you run a laptop off just the internal battery (to conserve power). You can change the settings, but you'll shorten your battery's working time between charges.
Under the speedometer. Push the trip meter reset button and the display will change from outside temperature to the odometer.
With a scan tool, or by turning the key on, off, on, off, on and watching the odometer display.With a scan tool, or by turning the key on, off, on, off, on and watching the odometer display.