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 troubleshootingSecurity indicator light circuit
Description
When the transponder key is registered, the transponder key ecu indicates the
key registration condition
by lighting up, blinking or turning off the security indicator.
Wiring diagram
Inspection procedure
Perform active test by intelligent tester (security indicator light)
...
If the shift lever cannot
be shifted from p
If the shift lever cannot be shifted with your foot on the brake
pedal, there may be a problem with the shift lock system (a system
to prevent accidental operation of the shift lever). Have the
vehicle inspected by your toyota dealer immediately.
The following steps may be used as an emergency ...
If your vehicle has to
be stopped in an
emergency
Only in an emergency, such as if it becomes impossible to stop
the vehicle in the normal way, stop the vehicle using the following
procedure:
Steadily step on the brake pedal with both feet and firmly depress it.
Do not pump the brake pedal repeatedly as this will increase the effort
req ...