Sorry for the delay, i had to do some digging to come up with the proper way to intiate the on board diagnostics on this model. Here is what I have found.
The automatic display feature allows you to read each module DTC display function in an automatic display sequence. Each system module DTC will be displayed for 3 seconds followed by a 1 second pause before the next DTC is displayed in an automatic sequence. If no DTC information is sent to the IPC from the system currently displayed on the IPC, the IPC will display NO CODES for that system. At any time during the automatic display function, the manual display feature can be activated by pressing any button on the DIC except the E/M 5 button. The E/M 5 button is used to completely exit the DIAGNOSTICS mode at any time. If there is a communications problem between any system, the IPC will display NO COMM when the IPC is trying to communicate with that system. When all DTCs have been displayed for all systems, the IPC will display NO MORE CODES for 2 seconds then will enter the manual display mode, waiting for manual mode operation.
Let me know how you make out. Good luck!
Honestly this is not a good way to determine the trouble codes as there are so many points in which bumping the wrong button and so on can cause you to overlook important information. Most techs that work with this advanced of a cadillac also have a scan tool to access information such as you are looking for. Personally I have not tried to utilize the onboard diagnostics in this particular model as I use a gm tech 2 scan tool. The manual does state that it can be done. This according to the manual is done through the drivers information center. I am thinking that the process of pulling trouble codes through the climate control system is something that stopped prior to this model. Here is how the manual states this is to be done. Let me know if this still does not help and I will opt out so other experts can assist.