For 2003 SC430: I just successfully erased all keys but the master and then reprogrammed my valet key using the procedures below:
Credits to http://www.keymam.com/ru/news_view.asp?newsid=58
TYPE E
Lexus Key and Remote Programming Instructions
Key Programming
1. Close all doors.
1a. lock and unlock the drivers door using the electric switch
2. Insert an already programmed master (BLACK) key into the ignition.
3. Turn the key in the ignition ON and OFF FIVE (5) times. - fast as you can
4. Open and close the drivers door SIX (6) times. - fast as you can
5. Remove the key from the ignition.
6. Insert the new key you want to program into the ignition.
7. Wait up to 2 minutes. The security light will be blinking for up to 2 minutes. When it stops blinking your key is programmed. To end programming step on the brake one time.
NOTE: You have 35 seconds to complete steps 1-5 and 10 seconds to complete step 6. If you do not do this procedure fast enough the car will not go into programming mode and your key will not program.
If the security light does not go out after 2 minutes start the procedure over again.
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Erase Key Procedure
If you need to erase existing keys, in the case of stolen or missing keys, follow the procedure below. This will erase all keys except for the master key you use during this procedure.
0. get inside the sc430
1. Close all doors.
1a. lock and unlock the drivers door using the electric switch
2. Insert an already programmed master (BLACK) key into the ignition.
3. Turn the key in the ignition ON and OFF SIX (6) times. - I did this as fast as I could
4. Open and close the drivers door SEVEN (7) times. - I did this as fast as I could
Note: The security LED flashed a few times
5. Remove the key from the ignition.
I recommend doing this procedure a couple of times to make sure it takes.
