Transponder 4C chip key program (add)

[Zeus253]

Hello, I would like to know the official procedure to correctly program/add new transponder 4C chip key/FOB using the existing non-FOB plain key (current single key does unlock everything and start vehicle). Again this is for 1998 Lexus LS400. I have been successful in adding the 3 button FOB remote portion but not start the vehicle. First person that has a successful procedure for me gets a prize. 

[paulo57509]

Remote entry programming and transponder programming are two different procedures (as you've discovered).

The attachments should be helpful.

key programming.pdf keyless entry programming.pdf

Edited April 1, 2023 by paulo57509
spelling

[Zeus253]

Thank you Paulo but when it comes to the step 5 - removing existing preprogrammed key, the security light starts flashing before I can go to step 6.

[paulo57509]

Is the key you're trying to program the rectangular FOB that's in the above image?  That doesn't look like any of the Lexus '98-'00 keys I've seen.

L: Transponder Key  R: Valet Key

[Zeus253]

I have the key on the right - it came with the car (starts vehicle and locks/unlocks everything). The one in my picture on bottom right is a compatible upgrade version (switchblade 4C type chip which is same as your L=transponder chip) to the OEM. From ebay showed as compatible. 

[Zeus253]

I am under the strong impression that if the key starts and does it all, rhat this is a master key.

[paulo57509]

15 hours ago, Zeus253 said:

I am under the strong impression that if the key starts and does it all, rhat this is a master key.

The Lexus logo key you have appears to be the Valet key.  It only opens the doors and starts the car.  It's not designed to unlock the trunk (via the trunk lid keyhole), the glove box or the button that's located on the dash between the trunk and fuel door release.

The transponder in the Valet key cannot be used to program additional keys.  You need the original, 3-button Master key (I mistakenly called it the transponder key in my previous post) that's matched to the ECU.

Read thru the links below; they should answer most of your questions.  You can also, do a topic search at Club Lexus (you may have to register) for more info. Keep in mind that the immobilizer was added to the LS sometime in '97-'98.

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/597869-programming-a-key-for-a-1999-ls400-is-this-correct.html

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/549508-key-dilemma.html