Does a Juvenile have the right to call parent before consenting to search of car?

My 17 year old son was stopped for a motor vehicle infraction midday while on his way to work. During the stop, the Police Officer mentioned that he smelled marijuana in the car and then went through the whole process of asking/informing my son if would consent to a Search of his vehicle and after my Son declined mentioning that he was already late for work, he was then given the ultimatum of either consenting to the Search or K-9 dogs will be called in. He then consented. The Police Officer had him walk back to his car so that he can read him the entire Consent Form before asking him to sign it. When done, my son asked politely if he could use his cell phone to call me before signing. He was told 'No you cannot'..