The former New York Mets player pleaded no contest in October (11) to allegations he tried to lease luxury cars from several Los Angeles dealerships last year (11) by providing fraudulent financial information.
The plea was part of a deal with prosecutors, which saw him charged with three counts of felony GTA and one charge of submitting false statements to a financial institution, while another 21 counts were dropped.
Dykstra faced up to four years in prison for the crimes, but last week (ends04Mar12) he attempted to change his plea to not guilty, claiming he was not fully informed about what he was copping to when he agreed to a settlement with authorities.
However, a Los Angeles Superior Court judge refused to allow the alteration and ordered him to serve three years in a California state prison.
He was taken into custody immediately after the hearing.
The GTA case was the latest in a string of legal problems for Dykstra - the former sportsman, who has been embroiled in bankruptcy proceedings, was also arrested in April (11) on suspicion of illegally removing and selling personal property from his home without official permission.
Actor Sheen came to his troubled friend's rescue at the time and reportedly posted his $150,000 (£93,750) bail.