Westipoo question?

i inherited a 9 mo old westipoo in aug of 07. i don't think he was loved as much as i love him and was kept outside most of the time. he is now housebroken and a great dog. lately he has been hiding under furniture when i try to get him to leave with me in the car. he loves to go for a ride so i don't know what is going on with him. i have never mistreated him and don't understand why all of a sudden he is acting like this.