You will need a class 2 scanner capable of running function tests to find the problem. Because the system is run through the body control module,there is little that can be tested with a 12 volt test light or a volt meter. A regular code reader won't do it as function tests need to be run on the system to find the failed component. I am enclosing the GM test procedure for you to take a look at, it may help and give you some ideas, but without the class 2 scanner it will be an up hill battle. Note, the blue high lights will not open for you, they are GM access only, thanks.
Sorry, may be under the hood, GM isn't very specific.
The fuses 5 and 6 are labeled IGN0 and CRUISE (they are OK). See image. I have an appt at the Dealer this afternoon, was hoping to avoid that with a simple fix. Found nothing in dash or inder hood labeled BCM.