Legal Question in Civil Rights Law in Illinois

Unless this house is also a commercial garage, the person holding it doesn't have legal rights to hold the vehicle under Illinois laws that protect "garagemen". However, if it is on his property and you try to get it back by just going there, technically you could be trespassing. You might try calling the police and have them meet you AND your sister at the person's house and bring the vehicle's title showing it was assigned to you. If the person can't produce evidence that he is entitled to retain possession of the vehicle by law and both you and your sister say what you say took place, then the police may be able to help you get possession of it back or the police may be able to charge the person with something in the nature of theft (wrongful detaining of property or whatever they may be able to call it). If the person attempts to sue for the repairs, you may have to get your sister to defend the case. If the police are unable to help, you will have to file a lawsuit - probably "replevin" based on your facts, to get possession back, but your sister may have to be involved since she's the one who delivered the vehicle to this person for the supposed repairs.