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 troubleshootingCoolant
Replacement
Remove no. 1 Engine under cover
Drain engine coolant
Loosen the radiator drain cock plug.
Hint:
Collect the coolant in a container and dispose of it
according to the regulations in your area.
Remove the radiator reservoir cap.
Caution:
Do not remove the radiator ...
How to proceed with troubleshooting
Hint:
Use these procedures to troubleshoot the supplemental
restraint system.
*: Use the intelligent tester.
Vehicle brought to workshop
Inspect battery voltage*
Standard voltage:
11 to 14 v
If the voltage is below 11 v, recharge or replace the battery
before proceeding.
...
Removal
Hint:
Use the same procedures for the rh side and lh side.
The procedures listed below are for the lh side.
Remove front pillar cover sub-assembly upper lh
Using a moulding remover, detach the 3 clips and
remove the pillar cover.
...