The engine immobiliser system is designed to prevent the vehicle from being stolen. This system uses a transponder key ecu that stores the key codes of authorized ignition keys. If an attempt is made to start the engine using an unauthorized key, the ecu sends a signal to the ecm to prohibit fuel delivery and ignition, effectively disabling the engine.

The transponder key coil receives this signal, the transponder key amplifier amplifies it, and then the signal is transmitted to the ecu. The ecu matches the key's id code with the vehicle's id code, which was previously registered in the ecu and then communicates the results to the ecm using sfi communication.
Engine immobiliser system
How to proceed with troubleshootingDtc check / clear
Check dtc
Connect the intelligent tester (with can vim) to the
dlc3.
Turn the ignition switch on and turn the intelligent
tester on.
Select the following menu items: diagnosis /
obd/mobd / immobiliser / dtc info /
current codes.
Check dtcs and then write them down.
Hint ...
Parts location
System diagram
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Disposal
Hint:
When scrapping a vehicle equipped with an srs or disposing
of the steering pad, be sure to deploy the airbag first in
accordance with the procedure described below. If any
abnormality occurs with the airbag deployment, contact the
service dept. Of toyota motor sales, u.S.A., Inc.
Caution ...