Garrison has pleaded guilty to charges of vehicular manslaughter without gross negligence, driving under the influence and providing alcohol to a minor.
In December 2006, Vahagn Setian was a passenger in Garrison's Land Rover when the actor lost control of the vehicle and crashed after leaving a pre-Christmas party. The 17-year-old was later pronounced dead in the hospital.
During a hearing at Los Angeles County Superior Court on Thursday, Judge Elden S. Fox ruled that he needed to see the results of a "diagnostic" test on Garrison before deciding his sentence.
Judge Fox also told the actor he has no interest in his celebrity.
He said, "The fact that you may have some notoriety, I don't really care."
Earlier in the day, the victim's father, Karen Setian, told the court that he feared a new TV advertisement Garrison has filmed warning against the perils of driving under the influence is nothing more than an attempt to get a lighter sentence.
Setian said, "He is an actor, and he is acting. Let's not fall for his act."
Garrison faces a maximum prison sentence of six years and eight months at a sentencing hearing scheduled for Oct. 31.
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