Legal Question in Criminal Law in California

No, entering the garage with the intent to steal the car completes the offense of burglary. Stealing the car is grand theft auto, a second and additional felony offense.

Any entry into a structure with the intent to commit a theft or a felony inside is burglary. Assuming it's a garage and not just a carport, you can be charged with burglary and theft of the automobile (either Penal Code section 487(d) or Vehicle Code 10851).

If the garage is attached, it's first degree burglary - much worse, since it carries up to 6 years in state prison and is a strike.