VATS delete: what it is and how to do it

VATS (Vehicle Anti-Theft System) is GM's immobilizer logic in the donor PCM. Swapped into a different vehicle, the PCM doesn't see the donor's key or theft module, so the engine won't start (or starts and dies). The fix is a VATS delete in the PCM calibration, done by a tuner (HP Tuners/EFI Live) or ordered with a pre-programmed swap PCM. It's part of the standard swap tune, along with injector/MAF data and transmission settings.