bought a used 1999 A4 Quattro 5V, 106k miles, only has 1 flip-style 2-button remote key, red button on side. the remote does not operate the doors. However, the key itself will lock & unlock drivers door and set alarm, however the key will not lock or unlock the pasengers door and the 2 rear doors. i have replaced the batteries in the keyfob and I even purchased a new remote keyfob and the remote buttons still do not operate the doors. there is not any noise in the actuators. what should I check out first?