Updated: Nov 13, 2019
When reading and writing a tune...
It is important to have a good battery on both your laptop and the vehicle. If either device loses power or connectivity during a write, your ECU may be damaged.
The key must be in the RUN position. Many newer vehicles will keep the ECU powered on for a period after the engine is shut off. The VCM Editor will begin writing to the ECU in this state. If the keep-alive time expires, and the ECU loses power during a write, your ECU may be damaged.
Don't open the doors, mess with the radio, windows, a/c, etc. while a vehicle is being flashed with a new calibration
Some Factory and Aftermarket radios have interfaces with the ECU to display things such as coolant temperature, Engine load, and many other parameters. If your vehicle is equipped with any device that requests data from the ECU in order to display a gauge, it will be important to pull power to that device. The CTS-V1 cars have such gauges built into the radio, and will take ~45 minutes to read / write if you fail to pull the fuse. This may even lead to a damaged ECU.
For some older vehicles, it is useful to power-cycle the ECU. When a write is complete, it is a good practice to turn the key off, and then Open / Close your driver's door so that the car will cut power to the ECU. Only one app can talk to the MPVI2 at once. If you have a phone connected over Bluetooth, or if you still have the VCM scanner connected for dataloging, the VCM Editor will not be able to communicate.