Your "Question" suggests a different concept from mine, so I'll explain my concepts and how I would use ISTA to address your FRM issue. THEN I'll suggest HOW to inspect/clean the Bus Connections at the FRM & JBE (Bus Hub), per the attached ISTA ScreenPrints.
ISTA is NOT part of "BMW Standard Tools" (which includes INPA for Diagnostics, NCS for coding, WinKFP for Programming/Flashing, and Tool32 (for a bunch of unknown things ;-). ISTA-D or ISTA+, also known as Rheingold, is "Dealer-Level" diagnostic software that can be installed on Windows OS Laptop, free download from MEGA, and a K+DCAN Cable ($50 from BimmerGeeks) is used to connect Laptop to E9x vehicle OBD II Socket. That cable can be used for most software connections to E9x vehicle (INPA, ISTA, NCS, etc.).
ISTA can be used to view "Documents" such as SSP wiring diagrams, REP repair procedures, etc., WITHOUT being connected to the Vehicle (OBD II Socket). However, to run any kind of "Diagnostics", the laptop MUST be connected to the Vehicle via K+DCAN Cable (or Wi-Fi/ BT Adapter). ISTA "Guided Troubleshooting" uses a "Flow Chart" method of "Diagnostics", and the initial step in that process is to connect to the Vehicle and read fault codes. THEN you select a particular fault code you want to diagnose. SO, you MUST be connected to vehicle to do that.
So to Emphasize: what you CAN do with ISTA, WITHOUT Cable/Wi-Fi/BT connection to vehicle:
RESEARCH: view documents, such as wiring diagrams, component locations, connector views, etc. ScreenPrint Examples of such documents were attached to Post #10 above, and also to this post.
FRM Bus Connections:
The FRM Module is connected to BOTH the PT-CAN Bus (PowerTrain) & the K-CAN Bus. I assume from the Definition of the "CDAB" code, and the Fault Info, linked in Post #10 above, that what should be checked is the PT-CAN bus connections between the FRM (Connector X14260, Pins #43 & #44, Red & Blue/Red wires) and the JBE Module (Connector X14271 [Blue], Pins #1 & #2). I have never "Checked CAN link" between two modules myself.
I would simply begin by disconnecting those two connectors, and inspecting the specific pins & sockets identified above (Red wire & Blue/Red wire at each). Look for any moisture, corrosion, enlarged sockets or anything preventing proper contact between pins/sockets, use Electronic Contact Cleaner to clean.
Since you can't connect to the FRM Module, it is also possible that the K-CAN Bus connections have issues. The two wires used for K-CAN Bus are (1) Green, & (2) Orange/Green. They are located in the SAME two Connectors, and are identified as follows:
FRM: X14260/45 (Green wire) & X14260/46 (Orange/Green wire).
JBE: X14271/10 (Green wire) & X14271/46 (Orange/Green wire).
So while you have those 2 connectors disconnected, carefully inspect/clean those pins/sockets as well.
Of course, after ALL THIS, your FRM COULD be "Fried" (mysterious internal Black Box failure).
Since you cannot connect to the FRM, and SOME of the FRM lighting functions work, THAT suggests a possibility of Bus connection issues, either in PT-CAN or K-CAN connections.
Wiring could PROBABLY be safely tested for continuity and short to chassis ground by using Ohms setting on Multimeter to measure Resistance between either end of Red wire at each separated connector; repeat for Blue/Red. Then test for Continuity to Chassis Ground at each of the wires at one of the connectors.
know any reason WHY that could damage anything, such as another Module that remains connected to bus? Better way to test for continuity or Short-to-Ground?
Attached are ISTA ScreenPrints showing PT-CAN bus wiring, and Connector Location and Connector view for FRM & JBE Connectors, so you can do the suggested inspection and cleaning.
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