How to Program a PassKey-III (PK3) Key

There were some posts in the automotive forums recently asking about how to program a PassKey-III (PK3) replacement key. 
After a bit of research, I have the following to offer:
Disclaimer: I have NOT personally tried these procedures, but have been told that they work on various GM vehicles.
First of all, the key looks like this: PK3 Key Picture (note the black plastic cover).  You should also see "PK3" stamped in the metal just below the plastic cover.  This key has a "transponder" in it that is used to enable the ignition and fuel systems.  Without a properly programmed key (or system programmed to accept the key), the van will not start or stay running.

From the service manual:
There are actually two procedures, but one involves using a programming tool which only dealers would have access to, so I am going to leave that one out.
30 Minute Relearn Procedure (Steps): This is for a "replacement" (new) key (no original available)

1) Insert a "Master" Passkey III (PK3) Key (the one with the black plastic cover as shown above).
2) Turn the Ignition to ON, but do NOT start the engine.  You should see the "Security" message on the dash for about 10 minutes and then it will turn off.
3) Turn OFF the Ignition and wait 5 seconds.
4) Repeat the above steps (1-3) a total of 3 times, or a total of 30 minutes.
5) After the third time (including turning back to the OFF position), start the van.  The van should now have "learned" the transponder information and will allow it to start and continue to run.
Important Notes:
- When the above procedure is used, all previously learned keys will be erased from system memory.
- Additional keys can be learned immediately after the relearn procedure.  This is done by inserting the additional key and turning the ignition to the RUN position within 10 seconds of removing the previously learned key

From another source (that provides PK3 keys): This is used to add a "duplicate" key (have original)
1) Insert the "Original" (working) Key.
2) Turn the Ignition to ON (RUN), but do NOT start the engine.  Turn the Ignition OFF and remove the key.
3) Within 15 seconds insert the new "duplicate" key and turn the Ignition to the ON position. The Security indicator should light for about 2 seconds to indicate that the new key has been programmed.
4) The new key should now be able to start and run the van.
- The manual seems to confirm this procedure except that the new key should be inserted and turned to ON (RUN) within 10 seconds.

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