Reactivation for Subsequent Owners
Push 
and follow the prompts to speak to an Advisor as soon as possible after acquiring the vehicle.
The Advisor will update vehicle records and will explain the OnStar service offers and options available.
See also:
Clock
To adjust the time and date:
1. Turn the ignition key to ACC/ACCESSORY or ON/RUN, then press to turn the radio on.
2. Press to display HR, MIN, MM, DD, YYYY (hour, minute, month, day, and year).
...
Add-On Electrical Equipment
Notice: Do not add anything electrical to the vehicle unless you check with your dealer first.
Some electrical equipment can damage the vehicle and the damage would not be covered by the vehicle's wa ...
Speedometer
The speedometer shows the vehicle's speed in either kilometers per hour (km/h) or miles per hour (mph). ...