I subscribed to the ALLDATADIY and followed the Symptom Related Diagnostic Procedures for Low Tire Pressure Indicator Always On and it appears to me that the BCM needs to be replaced.
Also in response to an earlier post, my mechanic hooked up his general purpose diagnostic scan tool and it did not detect any DTCs. It was an Autel tool, not a Tech-2. One thing that was strange was that his tool live data reading for the left rear tire pressure was in the 20 psi range like the other three, not 57.9 psi that my tool live data was showing.
We increased the pressure in my tires up to a little over 50 psi and it got the live data readings up to 27-28 psi which was equal to or greater than the 27 psi pressures that I selected for the recommended pressures. The Low Tire Pressure Indicator still stayed on.
Based on all this, I am leaning towards replacing the BCM.