Sounds like it needs reprogramming, or could be water in the reciever unit on the car.
Edit. this may be worth a try.
**You must have two original keys to perform this procedure. If you only have one key, you WILL have to take it to the dealer to get it programmed**
1. Insert and existing (working) key into the ignition cylinder.
2. Turn the ignition cylinder ON (RUN) and back to OFF. Ignition should stay on for at least ONE SECOND.
3. Remove the existing key and, within TEN seconds, insert a second working key and turn it to ON (RUN) and the back OFF. Ignition must be in ON for at least ONE second, but no more than TEN seconds. Remove the key.
4. Insert the new key before TWENTY seconds have elapsed and turn it to ON (RUN). Leave it the ON position for at least ONE second and turn back to OFF.
5. The security light will light up for THREE seconds to indicate that the new key has been successfully programmed.
6. To program additional keys, repeat steps 1 through 5