[ewill3rd]

A U1088 loss of communication with SDM doesn't mean much.
It means whatever module you retrieved that from did not recieve a state of health (SOH) message from the SDM for a given period of time.
If the code is history, ignore it.
Don't start tossing parts at it.
U codes pop up from time to time all over the place, rarely do I see a car that doesn't have some. U codes are worthless unless they are current or related to another problem that you might be having.

The SDM is the controller and sensor for the air bag system. It has circuitry that records crash data for retrieval if needed. They used to have all kinds of other stuff but these days it is just an SDM and some other sensors, and on CTS you'll find a PPS system for the passenger seat.
I don't know the time window that the SDM will record, and it is only set to monitor certain parameters. It takes special equipment to retrieve the data and it rarely gets examined these days.
I can assure you it doesn't work like everyone thinks it does or how the news wants you to believe.

A module that sets a current U1000 can be faulty and will usually require replacement but only if the code is CURRENT and causing a problem.