I own an Aurora, which of late has had some strange electrical issues, like trunk flying open when I lock the doors using driver side button, antitheft onstar not recognizing my key when in ignition, etc. I was told I needed a new ECU. Trying to get parts for this vehicle is nearly impossible. I finally received an ECU, removed my origanal one, only to find the company had accidentally programmed the replacement as a Pontiac. Took my car and both ECU units to a garage, and my original OEM ECU showed no fault codes and no freeze frame of fault codes. My question is, by removing my original unit did it completely reset? Because now mechanic is saying it's my timing belt my cam and crank sprockets and etc, since there appears to be no faults in units.
I'm afraid I'm not familiar with the Aurora but generally speaking, interrupting the power to an ECU will clear all fault codes and freeze frames so physically unplugging the unit will usually be enough to clear the codes.
The faults you describe would, in my mind, point more to a faulty with the BCU (Body Control Unit) which is typically responsible for functions such as central locking, electic windows, vehicle security, etc... Again, this is more generic advice and I don't know much about the vehicle in question.
I don't see how the tailgate opening itself or the onstar not recognising the key could have any relation to the cambelt or timing gear as this is only responsible for keeping the engine running. Attempting to plug an ECU into a car which is configured for a totally different vehicle may (but not always) cause issues.