Vehicles these days are loaded with computers, and most do all sorts of complicated jobs. They rely on hundreds of inputs and intricate networking to optimize total vehicle performance. The airbag computer, though, has to be much simpler and tougher to withstand the hardest of impacts while still recording data -- and it's just as tough to reset.
The first step to clearing the airbag computer is diagnosing the airbag system, and fixing whatever's wrong with it, if anything. The Supplemental Restraint Computer is a stand-alone unit with limited interaction with the body control module, and there's no way to clear the codes without removing the computer and connecting it to a very expensive and bespoke programming unit. Once you have it connected to the GM "key" programmer, you must then connect the "key" to a laptop, and go through and manually reprogram the computer to clear the faults and crash data. This requires not only the right equipment, but in-depth knowledge of the SRS computer programming itself.
If you're thinking that GM made this task almost impossibly difficult for a DIY mechanic, you're getting the right idea. It was an intentional attempt to keep DIY mechanics and unscrupulous car sellers from hacking and resetting a malfunctioning airbag system, or disguising crash data from later owners or insurers. Unfortunately, your quickest and safest bet is to take the truck to a GM stealership to have the system diagnosed and repaired. They'll clear the codes afterward. There are airbag system specialist companies out there who will clear the codes for you, but you'll have to remove the module and mail it off for reprogramming while your truck sits in the driveway.
