It depends on who owns the car. If the car is registered to the mother, then she has to right to allow the police to search the car. If the car is owned and registered to the 18 year old, then the mother cannot give permission to search the vehicle, only the owner can, unless there are extenuating circumstances which from your email does not appear to exist. If permission is not granted, the police would need a search warrant to search the car, although they could impound the car until a search warrant is issued.
Answered on Nov 14th, 2012 at 3:58 AM