Legal Question in Real Estate Law in California

There is no such thing as "standard" when parking is rented as an add-on rather than automatically coming with the unit. It could be part of one document. It could be a separate rental agreement for the parking. If separate it could have cross references and incorporation terms, or not. In short, they could be tied to each other or not, or it could be unclear, all depending on what the document(s) actually say. I can tell you that no matter what, you can't just cancel a rental agreement for parking without paying something for breaching the contract. What you would owe, and for how long, requires reviewing the document(s).

If you rent A and B, then sublet A, you still owe rent for B. Even if the apartment and the garage were part of a package deal, you're ultimately liable for the total rent or, put differently, both rents.