Might Not Be the ECM
You may experience a 2007-2012 Cadillac Escalade, ESV or EXT that has a P0633 DTC set in the ECM. Also, the Tech 2 will not be able to clear the DTC.
This code will set as an indicator that the ECM is in learn mode and not as a fault indicator. Any malfunction that causes a no-crank condition will prevent DTC P0633 from clearing. This DTC will clear upon a successful engine crank and start.
Prior to diagnosing the DTC or replacing the ECM, ensure that all power moding, VTD and engine cranking systems are operating correctly.