If you are a vintage GM enthusiast, a professional mechanic working on LT1/LT4 engines, or a DIYer trying to resurrect a C4 Corvette, a 3rd-gen Camaro, or a square-body truck, understanding this tool is not just helpful—it is essential. This article dives deep into what Mode 22 is, why Terry’s tool became an industry legend, and how it can save you hours of diagnostic headaches.