Being arrested on new charges while on parole in California puts someone in two separate but simultaneous legal problems, and both of them are serious.
The first is the parole violation itself. Parole is a second chance granted by the same judge who sentenced him the first time. That judge signed off on parole as an option and is now watching it come back as a failure. When a parolee picks up new felony charges, the parole board can revoke parole and send him back to finish whatever remained on his original sentence. That remaining time gets served first, before anything related to the new charges even begins.
The second problem is the new charges themselves. Transporting a controlled substance under California Health and Safety Code 11379(a) is a felony carrying two to four years in state prison. Possession of a stolen vehicle under Penal Code 496D(a) is a wobbler, meaning it can be charged as either a felony or a misdemeanor depending on the circumstances and the prosecutor's discretion. As a felony, it carries sixteen months to three years.
Stack those together with the remaining parole time and you are looking at a significant cumulative sentence. The exact number depends on how much time he had left on parole, whether the new charges are run consecutively or concurrently, his prior record, and how aggressively the DA decides to pursue it.
The judge who originally sentenced him is not going to view this favorably. Leniency was extended once and was not honored. That history matters at the next sentencing hearing, and a hard line from the bench is a reasonable expectation. He needs an experienced California criminal defense attorney immediately if he does not already have one.