Did the police officer exceed the scope of the search?

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated. First of all, since we do not have all the facts, it is not really possible to answer with complete accuracy. How was the search conducted? Did they have a search warrant? Was there probable cause for the search. I strongly suggest that you contact an experienced criminal defense attorney for a face-to-face consultation and give him/her all of the facts surrounding your brother's case. He/she would then be in a better position to analyze his case and advise you of your options.

Exceed the scope. No, and he will write a report that ensures he had probable cause way above and beyond his general authority to search. They are trained how to write those reports. When charged with any crime, the proper questions are, can any evidence obtained in a test, search or statement be used against you, can you be convicted, and what can you do? While this isn't a 'capital case', it certainly carries potential time, so handle it right. No amount of free 'tips and hints' from here or elsewhere are going to effectively help in a legal defense. If you don't know how to represent yourself effectively against an experienced prosecutor intending to convict, then hire an attorney who does, who will try to get a dismissal, charge reduction, diversion, programs, or other decent outcome through motions, plea bargain, or take it to trial if appropriate.

If they had a search warrant or he was on probation with a search condition which included his car they could search wherever they want.

Law enforcement officers need a warrant, probable cause, or consent to search. The warrant and consent can specify a limit to the search. Probable cause will be limited only to the limit of the cause.

No, under these facts, the officer had the right to search underneath the vehicle. Of course, these cases depend on the facts of each case, so the facts would need to be explored further to see if the search was truly valid. For example, if your brother was unlawfully detained, or that detention itself was prolonged to conduct the search, there may be an issue that could lead to the suppression of the drugs found in the search. But generally, once the officer has probable cause or consent to search, there's no real limitation on the extent of that search. And once he is arrested, the vehicle will be impounded and another "inventory search" will be conducted that can be much more complete.