Land Cruiser Model 100 Intermittent Security Light/Immobilizer Issue

Jul 29, 2017
Washington DC USA
My 2000 Land Cruiser has 4 master keys and one valet key programmed into the ECU.
With the car cool, all five keys turn the security indicator light off and start the car.
If I drive the car a few miles and turn it off, none of the MASTER KEYS will work. But, the VALET key still works (Security indicator light goes out after one second and car starts)
Let the car cool and all keys work again to turn off the security indicator light.

This is not the famous EFI fuse/relay problem. I've disassembled and reassembled the fuse/relay box (a non-trivial task). I can hear and feel the EFI relay pulling in and dropping out when I insert and remove ANY key, even one that has not yet been cut.

I've unplugged and replugged the ECU connectors many times. I have not yet fiddled with the transponder key coil or amplifier connectors.

What is different between a master key and a valet key that could possibly explain this?
Does the ignition switch itself detect the slight mechanical difference between masters and slaves? If so, does it send this status to the ECU?
Has anyone used a protocol analyzer between the transponder key amplifier and the ECU?

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