If you’re an OnStar Member, you can set up an account in your vehicle Owner Centre or tie your OnStar service plan to your existing account. Visit your GM Account and follow the instructions there.
How do I find my OnStar account number?
You can push your blue OnStar button, call 1.888.4ONSTAR (1.888.466.7827), visit your account on the Owner Centre or refer to your OnStar monthly diagnostics report for your OnStar account number.
My OnStar Account Help | Help And Support | OnStar
