Two things to check:

Replace the fob batteries or reprogram. Here's how to reprogram them:

Connect a scan tool.
Select diagnostics.
Select body code.
Select body style code.
Select other.
Select remote function actuator (RFA).
Select special functions.
Select F0 program key fobs.
Choose the fob number that you wish to program.
Follow the screen prompts in order to complete the programming procedure.
Press and hold the lock and the unlock buttons on the transmitter being programmed. The door locks will cycle. This should take about 15 seconds.
Proceed to the next transmitter and repeat steps 1-11 until all of the transmitters are complete.
Exit the remote keyless entry (RKE) programming.
Disconnect the scan tool.
Cycle the ignition. Test the transmitters for proper operation.