From the Service Manual (for an 07 ... no idea if it differs for earlier)
CUSTOMER LEARN METHOD
NOTE: The Customer Learn feature is only available on domestic vehicles, or those vehicles which have a U. S. country code designator. This programming method also requires access to at least two valid Sentry Keys. If two valid Sentry Keys are not available, or if the vehicle does not have a U. S. country code designator, the Secured Access Method MUST be used to program new or additional valid keys to the SKREEM.
The Customer Learn programming method procedures are as follows:
1. Obtain the blank Sentry Key(s) that are to be programmed as valid keys for the vehicle. Cut the blank key(s) to match the ignition switch lock cylinder mechanical key codes.
2. Insert one of the two valid Sentry Keys into the ignition switch and turn the ignition switch to the ON position.
3. After the ignition switch has been in the ON position for longer than 3 seconds, but no more than 15 seconds, cycle the ignition switch back to the OFF position. Replace the first valid Sentry Key in the ignition switch lock cylinder with the second valid Sentry Key and turn the ignition switch back to the ON position. The second valid Sentry Key must be inserted in the lock cylinder within 15 seconds of removing the first valid key.
4. About 10 seconds after the completion of STEP 3, the security indicator in the instrument cluster will start to flash to indicate that the system has entered the Customer Learn programming mode.
5. Within 60 seconds of entering the Customer Learn programming mode, turn the ignition switch to the OFF position, replace the valid Sentry Key with a blank Sentry Key transponder, and turn the ignition switch back to the ON position.
6. About 10 seconds after the completion of STEP 5, the security indicator will stop flashing, stay ON solid for 3 seconds, then turn OFF to indicate that the blank Sentry Key has been successfully programmed. The SKIS will immediately exit the Customer Learn programming mode. After the ignition is cycled the vehicle may be started using the newly programmed valid Sentry Key.
Each of these steps must be repeated and completed in their entirety for each additional Sentry Key that is to be programmed. If the above steps are not completed in the given sequence, or within the allotted time, the SKREEM will exit the Customer Learn programming mode and the programming will be unsuccessful. The SKREEM will also automatically exit the Customer Learn programming mode if it sees a non-blank Sentry Key transponder when it should see a blank, if it has already programmed eight (8) valid Sentry Keys, or if the ignition switch is turned to the OFF position for more than about 50 seconds.
NOTE: If an attempt is made to start the vehicle while in the Customer Learn mode (security indicator flashing), the SKIS will respond as though the vehicle were being started with an invalid key. In other words, the engine will stall after about two seconds of operation. No faults will be set.
NOTE: Once a Sentry Key has been programmed as a valid key to a vehicle, it cannot be programmed as a valid key for use on any other vehicle.
and just FYI
Remote entry programming
STANDARD PROCEDURE - RKE TRANSMITTER PROGRAMING
New Remote Keyless Entry (RKE) transmitters can be programmed using the scan tool and the proper Diagnostic Procedures manual. The scan tool can provide confirmation that the PCI data bus is functional, and that all of the electronic modules are sending and receiving the proper messages on the PCI data bus.
The following procedure can be used as long as one programmed transmitter is available:
NOTE: When entering program mode using that programmed fob, ALL currently programmed fobs will be erased and they will have to be reprogrammed for the vehicle. If program mode is entered and no action is performed, the previously programmed fobs will continue to function.
1. Enter the vehicle and close all doors.
2. Fasten the seat belt (this will cancel the seat belt chime). Turn the ignition to the RUN position.
3. Press and hold the UNLOCK button on a programmed transmitter for 4 to 10 seconds. Within the 4 to 10 seconds with the UNLOCK button still depressed, press the PANIC button for one second. When a single chime is heard, release both buttons. The chime indicates the system is in program mode.
4. Press and release both the LOCK and UNLOCK buttons simultaneously on a fob to be programmed. A single chime will be heard, this indicates the fob has been recognized.
5. Press and release any button on the same fob. A single chime will be heard, this indicates the fob has been programmed.
6. Repeat steps 4 and 5 for up to a total of 4 fobs.
7. Turn the ignition OFF.
8. Turn the ignition ON or wait 60 seconds.
The vehicle will remain in program mode for up to 60 seconds from when the original chime (step 3) was heard. After 60 seconds, all programmed transmitters will function normally.