First let me say that if you don't have a real symptom, those U codes are wasting your time. Ignore them and move on.
U codes are communication codes, modules set them when they lose communication with another module. Meaning, while modules are active they send out a "SOH" or State of Health message to other modules on the bus, sort of like "checking in" to make sure they are still there.
On Class 2 systems this begins when the key is turned on, all the modules send out an SOH and the other modules that use their information note that they have received a SOH from that module for the rest of the key cycle.
If for some reason a module stops sending out a SOH message, any module that uses information from it will set a DTC in this format
U- means it's a communication code.
1- means it's a GM specific code (ANSI codes have a leading 0)
016- this is the module identifier, meaning the module that stopped sending a SOH. 016 is the PCM by the way. If you saw two instances of U1016 that means that two modules did not see a SOH from the PCM. Now if this accompanies a problem, like error messages or freaky electronic problems then you can use U codes to your advantage. If you are just checking codes for fun, and you find U codes, they are usually worthless.
Now that being said, do you have any symptoms or were you just checking codes?
The reasons i posted this question is because a few weeks ago i pulled into a gas station and my car suddenly died. I checked the oil tranny fluid etc. all was fine, so i contacted Onstar and had them do their diagnostic test. They said that everything was fine. Today i was driving through town and my car died again, then about 5 mins later the right side speakers cut off for about 5 or 6 secs. and now the radio wont store any of my tone settings.