I have been studying this thread to learn how to troubleshoot my issue. One of the few threads that actually diagnoses an issue from start to finish.
https://www.e90post.com/forums/showthread.php?t=2121740
I was able to pull the PT CAN wiring diagram using ISTA.
1. Do I test these wires at the connector for each module? Are the tests done with the connectors plugged in or removed from the module?
2. Am I looking for voltage, ohms, something else? One data point I can't find is the normal values for the tests. Is that information also in ISTA?
3. Do I need an oscilloscope?
In the meantime, I am going to get my car in the air and start removing panels to do visual inspections where possible. There is a location identified in the thread I linked which points to the wheel well that I want to look at just to rule it out.