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 tire pressure warning ecu
Disconnect the e56 ecu connector.
Measure the voltage and resistance of the wire
harness side connector.
If the result is not as specified, there may be a
malfunction on the wire harness side.
Reconnect the e56 ecu connector.
Measure the ...
Removal
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.
Remove no. 1 Engine cover (see page es-410)
Remove air cleaner cap (see pag ...
Pressure control solenoid "d" performance (shift solenoid valve slt)
Description
The throttle pressure that is applied to the primary regulator valve (which
modulates the line pressure)
causes the solenoid valve slt, under electronic control, to precisely modulate
and generate the line
pressure according to the extent that the accelerator pedal is depr ...