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 troubleshootingCircuit opening relay
On-vehicle inspection
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.
Inspect instrument panel junction block
Notice:
Th ...
Headlight relay circuit
Description
When the light control switch, located on the headlight dimmer switch, is
turned to the head position, the
head relay illuminates the headlights.
Wiring diagram
Inspection procedure
Perform active test by intelligent tester (headlight)
Connect the intelligent tester ( ...
Open in stop light switch circuit
Description
The skid control ecu detects the brake operating conditions through a signal
transmitted by the stop light
switch. The skid control ecu incorporates an open circuit detection circuit.
This dtc is set under either of
the following conditions:
An open is detected in the stop lig ...