It's no more or less complicated. It's just that the check engine light is for the PCM only. ABS & SRS have their own modules and warning lights. Code readers and entry level scan tools can only access very limited areas of the PCM. On a decent scan tool, there's more stuff that you can't access, than what you can. If you've never seen a high end scan tool in action, you'd be amazed at the data it can access. Some of them will access a little known module called the CDR module, (Crash Data Recovery). GM has been using them in certain models since 1994. All 1998 and newer S/T have them http://www.boschdiagnostics.com/dsof...ist_R1_0_0.pdf