RedGemini

It's all located in the electronic (fob) part inside the key shell. I ordered a replacement flip key (shell) for my '05 RX330 from 1010keys on eBay (he only sells Lexus keys). I supplied they key code and a picture of my current blade (send via iMessage/text to the number provided in the listing). He cut the key and shipped it for $22. It was very quick processing and delivery. I popped open my old key with the fob, and put the chip inside the new flip key shell. Works like a charm. No programming needed.

http://www.ebay.com/itm/152321909123?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Bytheway

This is a picture of my keys showing you the location of the transponder (immobilizer) chip.
Hope it helps

Teamshorb

I can only speak for the 2002, SC430 but I ordered 2 keys (with FOB) from Amazon. I went to my local lock smith to have the FOB programmed to my car. The technician got a "Unknown Communication Error" nlt999's post was a HUGE help because it pointed the way to eventually finding the correct answer. The part number consist of 2 parts. The first is the RFID chip that lets you start the car. That part number is 1551A. That is the only RFID chip the 2002 SC430 will accept. The second part is the FCC number for the RF transmitter in the FOB (Door/trunk opener) That part number is 12BBT. So... The correct key part number is

1551A-12BBT.

Almost everywhere you look they are going to try to sell you the 1511A-12BBT. Like I said above, I got 2 of these from Amazon and they did not work. I purchased the 1551A-12BBT off Ebay and the locksmith programmed it the first time. I should note that I had the locksmith also order a key for me while I was figuring this out. The key his supplier sent him did not work.,
Then he tried my ebay OEM 1551A 12BBT and it programmed and the car started. Next he programed the FOB and Beep-Beep the door locked and unlocked.

All in
$24.00 for 2 Blank keys from Amazon
$30.00 to have the keys cut
$44.00 for the correct Fob from Ebay
$85.00 to have the key programed to the car.
---------
$186.00 Not what I call a great savings especially when you add in 30 hours of research and the extra money I spent on parts that don't work.

TMI Section:
If you break open one the the FOBS, you can see the PCB with all the electronics for open the car doors. If you remove the PCB you can see a little black not quite square chip tucked into the side of the case. This is the RFIC chip that lets the car start. I've attached a picture of a key fob that has been taken apart. You can see the little RFIC chip.

Bottom line, there is a lot of bad information out there about what it the correct part for an 2002 SC430.

I hope this helps
Doug