Well, generally a term of someones probation includes "obeying all laws." So, if they are arrested for public intoxication, or disturbing the peace, etc. that can violate probation. But if a driver was pulled over, and the passenger was not breaking any laws, then there should not be any issue. Keep in mind that some people have additional conditions of their probation, such as "abstain from drinking...." If that is the case, and they violate one of those conditions, then they could be found in violation of probation.
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Mr. Hache is correct. It really depends on what the terms and conditions of probation are for the passenger to determine if there has been a violation of probation. If no terms were violated then has not been a violation of probation.
Normally a person with a DUI conviction is on informal probation, which means they'll only get in trouble for any misconduct if it comes to the Court's attention. If you weren't arrested, then it's doubtful it'll come to the Court's attention. However, if you were arrested, then it'll be a question of whether or not your conduct violated any terms or conditions of your probation. If that's the case you should consult a local attorney to see what can be done to mitigate your situation.
If you're on formal probation, meaning that you report to County Probation, then you're probably required to report contact with law enforcement regardless of the circumstances. Then it'll be a question of whether or not your probation officer considers your conduct in violation of the terms and conditions of your probation. Good luck.