try this first..
1. First use the following procedure to try and program the key fobs:
A) Turn the ignition from OFF to RUN five times within 10 seconds, ending in RUN. If the Generic Electronic Module (GEM) has successfully entered program mode, it will lock and unlock all the doors.
B) Press any button on a keyless entry remote transmitter and the doors will lock and then unlock to confirm that each keyless entry remote transmitter has been programmed.
C) If the door locks do not respond for any keyless entry remote transmitter, wait for several seconds and press the button again.
D) Turn the ignition switch to the OFF position, or wait up to five minutes after step 1, to exit program mode. If a keyless entry remote transmitter has been programmed (or reprogrammed), the GEM will lock and unlock all the doors one last time.
2. If the vehicle will not enter the programming mode, verify that it is equipped with the factory keyless entry system. The easiest way to do this is access the driver's power lock switch wiring and connector (connector C505). The connector is a 7 terminal connector on both models. However, if the vehicle is not equipped with factory keyless entry, there will be 7 wires, with pin 4 being a Black/White (BK/WH) battery voltage feed wire. If it is equipped with factory keyless entry, there will only be 5 wires in the connector with pin 4 being a Black (BK) ground wire. If the vehicle is not equipped with factory keyless entry, the customer is most likely using an aftermarket keyless entry or remote start system.
3. If the vehicle is equipped with factory keyless entry but the GEM will not enter the programming mode, check fuse #8 and #19 in the Central Junction Box (CJB) (interior fuse panel) with a voltmeter for any stray voltage with the key off. In some cases due to corrosion or moisture in the CJBs, the ignition feed fuses can have voltage on them with the key off causing the GEM to not recognize the key has been turned off. If present, remove the CJB and check for any water or corrosion problems.