01 OEM Keyless entry

Alright guys maybe you can help me out....My OEM remote for my stang has gone bad! Well I'm not sure if its the remote because both have the same problem. I have changed the battery on both and I have to be almost beside the car for it to work? Would it be the remotes or would it be the reciever in the car what do you guys think? Would Ford check it at no charge? my stang has 48,000 miles and according to my car fax report it says that its still has warrenty for some components would that be one of them? My brother has an 03 explorer with 30,000 miles and his works from almost a block away Thanks guys.

Tony