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 troubleshootingFuel tank
Components
Removal
Discharge fuel system pressure (see page
fu-9)
Disconnect cable from negative battery
terminal
Caution:
Wait at least 90 seconds after disconnecting the
cable from the negative (-) battery terminal to
prevent airbag and seat belt pretensioner activation.
...
Dtc check / clear
Check dtc (when using intelligent tester)
Connect the intelligent tester (with can vim) to the
dlc3.
Turn the ignition switch on.
Turn the tester on.
Read the dtcs by following the prompts on the
tester screen.
Hint:
Refer to the intelligent tester operator's manual for
furth ...
Terminals of ecu
Check power steering ecu
Hint:
Measurements cannot be performed on the c connector
side of the power steering ecu.
Measure the voltage and resistance of the
connectors.
If the result is not as specified, the ecu may have a
malfunction. ...