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 troubleshootingTerminals of ecu
Check occupant classification ecu
Measure the voltage of the connector.
...
Removal
Hint:
Use the same procedures for the rh side and lh side.
The procedures listed below are for the lh side.
When removing the moulding, heat the vehicle body and
moulding using a heat light.
Standard heating temperature
Notice:
Do not heat the vehicle body and moulding
excessively.
...