"Diagnostic Alert" while truck is off?

[Michiganron]

Is it possible for my 2021 Silverado to send me a diagnostic alert text message if it is powered off?

Last night I received a text message diagnostic alert indicating low air pressure in one of my truck tires. My truck is in for service right now and there is no reason it should have been turned on that late at night, as the business was closed.

Is it possible for me to receive a text message diagnostic alert when the truck is not running, or should I be concerned that someone at the shop had started my truck at nearly 10pm?

[Michiganron · Accepted solution]

Mystery solved. Sharing here in case anyone else runs into something similar...

I spoke with an OnStar rep yesterday. After doing a bit of research she informed me that my truck is equipped with an "11th generation" OnStar that will perform a "sleep cycle" diagnostic if powered off between 3-5 days. 

The dealership was closed Monday for MLK Day. Since the truck had not been powered on for at least 3 days it must have run the "sleep cycle" diagnostic at nearly 10pm, triggering the text message about my tire having low pressure.