Mode 22 Scan Tool By Terry - Gm

Is the software perfect? No. You’ll need patience to find a working download and to configure your serial connection. But once it’s running, you will wonder how you ever diagnosed a GM “Check Engine” light without it.

Terry’s original tool was written for Windows 95/98/XP. However, modern versions or community updates run on Windows 10/11 in compatibility mode. Install the FTDI or Prolific drivers for your USB-to-serial adapter. gm mode 22 scan tool by terry

Plug your USB ALDL cable into the port. Pins A and B (top two rightmost pins) are typically the ground and data lines, but quality cables auto-detect. Is the software perfect

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. Before discussing the tool, we must understand the protocol. In the early days of engine control computers (ECUs), GM developed a proprietary data stream to communicate with its electronic control modules (ECMs, PCMs, and BCMs). This system operates on a single-wire, 8192 baud (8.2kbps) data line—often accessed via the Assembly Line Diagnostic Link (ALDL) connector under the dashboard. But once it’s running, you will wonder how

| Tool | Protocol | Price | Best For | |------|----------|-------|-----------| | | ALDL Mode 22 | Free | Budget, simple diagnostics | | Scan9495 | ALDL Mode 22 | $30 shareware | LT1/LT4 specific (94-95) | | TunerPro RT | ALDL + OBD-II | Free (donation) | Advanced tuning & logging | | ALDLLogger | ALDL Mode 22 | Free | Mac/Linux users | | Tech 1 w/ GM cartridge | All GM modes | $500+ used | Professional restoration |

For decades, General Motors vehicles (GM, Chevrolet, Buick, Cadillac, Pontiac, Oldsmobile, GMC) have relied on a unique and powerful data stream known as Mode 22 . While generic OBD-II scanners can read basic engine codes and live data on vehicles from 1996 onward, older GM models (primarily 1980–1995) and even some early OBD-II systems speak a different language. Enter the legendary solution: The GM Mode 22 Scan Tool by Terry .