If you look at the "Democracy" that is the underlying principle of Single Wire Serial Communications depicted in this Class 2 Network Diagram below... You can see that the Radio is displayed
Way down in the Far Right hand Corner... while the BCM occupies the space Way up in the Upper Left hand Corner of the same Diagram. But...
All of the "Serial Data Lines" from each Module eventually 'Meets Up in The Middle':
The GM Class 2 "Star Topology" Communication Protocol means that
ANY Module can communicate on this Network as soon as there is a Minimal Clock Cycle Break in the Pulsed Signalling on that One Wire and after the Priority Order for "chatting" has been met.
So ANY one of them can then be in command and Take the Network HIGH to around "7" Volts DC from the quiescent state of "0" Volts DC to be able to Transmit and Receive Data.
It follows on that if any ONE Module Shorts to Ground OR even if it Shorts to B+ Positive Voltage, well above "7" Volts DC during any 'Bad Moments',
it alone can take the ENTIRE Network Down; whether HIGH or Low. In this regard, the GM Class 2 Network is an 'Equal Opportunity Offender' in such instances.
However, during ordinary Operations there is NO ONE Over-Arching "Module Dictator" telling which of the Modules gets to 'speak' over others at any given time. "Un-Corking" the Class 2 Network Splice Pack Combs
SEVERS this influence in between
ALL Modules on the Network, until the "Single Wire" interface is restored. If the BCM is one of those Removed Modules... it can have NO Further Influence on the others.
Naturally, some Modules MUST take precedence over others, depending upon their Absolute Necessity for the Safe Operation of the Vehicle. The PCM and the BCM have a lot to say about that and which Modules will command under these situations.
A Perfect Example occurs whenever the Engine Operations go instantly into "Limp Mode" if there is even the
slightest disagreement between the ACC Pedal Module and the Throttle Body Module
not reconciling their Physical Positions with the Throttle Plate Position Signals in between each other and the PCM.
As it concerns the Anti-Theft programming between the Radio and the BCM... Normally, it runs that security check each and every time the Vehicle is Started so that after exchanging the confirming information, the BCM can allow the Radio to function properly.
However, a BCM can malfunction and become "The Fly in The Ointment". BCM Modules DO Fail from time to time and in some cases, installing the BCM from ANOTHER similar Vehicle as a replacement will likewise NOT work unless it gets Added to the System using a "GYMKO" Tech 2 Scan Tool.
It is usually necessary to ensure a common Vehicle VIN assigned inside the PCM will agree with the BCM. YMMV with this as the outcome depending upon which GM Vehicle is involved after installing a "Junk Yard" BCM and finding out if it will Function Properly...
or NOT.
Also, if someone Swaps in a Different Radio
(...that has possibly been stolen from another vehicle...) it will NOT work until it has been correctly added-assigned as a New Module to the Network via the "GYMKO" Tech 2.
You have not mentioned whether or not the Radio in the 2003 Cadillac Escalade is an OEM version, or an After-Market Unit. THAT information might be relevant to its present behavior whenever the Network goes sideways for any reason.
All of this intermingling of disparate GM OEM Control Modules is impossible to achieve without having access to the right High End Scan Tools to Diagnose the System... and access to the ACDelco TIS2WEB or TIS2000 SPS Software if needs be to be able to Download and Install New Calibrations that satisfy ALL their Module Functionality and Security Issues.