Commercial software suites charge hefty annual subscription fees or lock usage behind proprietary hardware tokens. Terry’s tool offers a community-driven, transparent alternative. It gives mechanics full control over the diagnostic commands sent to the car. This flexibility makes it a staple for platform-specific diagnostics on classic LS engine swaps, late-90s trucks, and modern GM performance platforms.

Terry’s tutorials are famous for teaching people how to fix specific GM problems using affordable tools.

1995 K1500 truck won’t pass emissions. Solution: Terry’s tool reads the proprietary Mode 22 O2 integrator and block learn values. Fuel trims are stuck at 160 (rich). You find a leaking fuel pressure regulator through the vacuum line—a code a generic scanner would miss.

Monitoring transmission fluid temperature (TFT) and pressure control solenoid (PCS) duty cycle.

: Turn the vehicle’s ignition to the ON position (engine off or running, depending on your test criteria) and click "Connect". Troubleshooting Guide

Who it’s for

Essential data points for engine tuning and performance optimization.

The GM Mode 22 scan tool, developed by Terry, is a specialized diagnostic tool designed for General Motors (GM) vehicles. This report provides an in-depth analysis of the tool's features, functionality, and benefits, as well as its applications in the automotive industry.

What it is

The is a highly specialized, free legacy diagnostic software program designed to extract advanced manufacturer-specific data from General Motors vehicles. While standard OBD-II tools are limited to generic emissions data (Modes $01 through $0A), this utility leverages GM’s proprietary Mode $22 protocol to request specific diagnostic data identifiers (PIDs) directly from the Powertrain Control Module (PCM).

With enhanced GM PID files, Torque Pro can act as a modern Mode 22 scanner. ScanMaster ELM: A robust diagnostic program.

To appreciate why Terry's software became a staple on early diagnostic forums, it helps to understand how OBD-II communication is structured. The Society of Automotive Engineers (SAE) establishes specific diagnostic modes, numbered in hexadecimal format:

Based on the existing reputation of "Terry" (likely Terry Johnson of ) and his existing software (Terry's GM Scan Tool), the most logical and high-impact feature to add would be a "Bi-Directional Smart-Actuator Dashboard."