It has been two weeks, have yous solved your engine brake issue?
You did not specify the FMI for your fault but for SPN 523531 FMI 31 Troubleshooting manual shows description as "Extra Sub bus switch" details "Active when one or more sub bus switches are plugged in that do not have a corresponding MSF parameter." Action : With the key ON, connect to the vehicle with ServiceLink or DiagnosticLink. Go to the MSF "Switches" screen or panel and note which switches are marked as extra. For each extra switch, determine whether or not the vehicle should have that switch installed. If it should be installed, set the appropriate MSF parameter (based on switch ID) to make that switch "available." If it should not be installed, find the switch on the vehicle and remove it.
Again for SPN 973 you did not specify the FMI so I am attaching all three of FMI's for SPN 973. Read them over and maybe check if the electrical harness is to your engine brakes switches are fully connected and in proper position. Otherwise, it appears your going need someone with Diagnostic Link to solve the problem