The immobiliser is a function, the transponder being read from the key by a module, to the BSI and BSI sending via canbus to ECU to unlock (this is encrypted between the BSI and ECU - they are a matched pair in factory). It is not really a module, but it is a series of ECU involved and a process to get to unlocked / start okay by the ECU.
A function of
BSI to have the key transponder recorded it (this can be done only one)
BSI to read the transponder from the module responsible, and assuming synced, to provide the unlock to ECU to start.
If not detecting you stepping on the brake, this is twin switch and may work for the lights, but not be working correctly.
The BSI and ECU are matched pair in the factory or else immobiliser function cannot be read (this is encrypted at factory and never the same between vehicles)
It is not clear from your post the problem, the damage that was present, the DTC present or the history the got you to
help with the for final repairs everything is ready
I'm not trying to cover in-between module like ABS which, if an error is present, may bring communication down.
But I can't access the immobiliser.
You need to be clear about what you're using to access (ie the diagnostics tool and software possibly)
Hope you find this useful.
