For owners and technicians working on 1980s to mid-1990s General Motors vehicles (especially those with the 8192-baud ALDL data stream), the "GM Mode 22 Scan Tool by Terry" remains a legendary piece of DIY diagnostic software. Unlike generic code readers that only retrieve "Check Engine" codes, Terry's tool provides a deep, real-time look into the inner workings of early GM electronic control modules.
Designed specifically for 8192-baud ALDL GM vehicles, typically:
Terry’s tutorials are famous for teaching people how to fix specific GM problems using affordable tools.
“If you’re still trying to diagnose transmission or ABS problems with a generic code reader, you’re guessing. Mode 22 turns guessing into graphing. Invest in a real scan tool, learn a dozen key PIDs, and you’ll fix in one hour what used to take three.”
For the DIYer: Look for used GM Tech 2 clones or an Autel AP200 (which supports limited Mode 22 on GM). For the pro: Master Mode 22, and you’ll be the person on the forum everyone asks, “How did you find that?”
Author’s Note: Thanks to Terry and countless GM master techs who shared Mode 22 PID lists on forums like Gearhead-EFI, LS1Tech, and the now-defunct GM TechTrain listserv. The data is old, but the protocol is still gold.
The GM Mode 22 Scan Tool by Terry is a specialized, often free software utility designed for deep-level diagnostics on General Motors vehicles, typically used in conjunction with low-cost ELM327 OBD2 interfaces. Overview of the Tool
Unlike generic OBD2 scanners that only read "Mode 01" global data, this tool targets Mode 22, a manufacturer-specific diagnostic mode used by GM to provide access to enhanced data parameters (PIDs) not available through standard protocols.
Platform Compatibility: It is frequently bundled with ELM327 USB or Bluetooth diagnostic kits as part of a free software suite.
Target Audience: It is primarily aimed at DIY enthusiasts and older GM vehicle owners who
Key Capability: It enables users to view proprietary sensor data that generic tools might miss, such as specific transmission temperatures, ABS data, or body control module (BCM) status. Functionality Comparison
While "Terry's" tool is a lightweight utility, it sits between basic code readers and professional factory equipment: OBD II Generic PID Diagnosis - MOTOR Information Systems gm mode 22 scan tool by terry
If you own a 1982–1995 GM vehicle with TPI, TBI, LT1, or Crossfire Injection, the GM Mode 22 Scan Tool by Terry is not a luxury—it is a necessity. Cheap generic readers will lie to you or show blank data. Professional Tech 2 or GDS2 tools will refuse to communicate. Only a dedicated Mode 22 tool bridges the gap.
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.
For the price of a USB ALDL cable (around $40-60), you can have dealer-level diagnostics from the early 1990s. Terry may not have a corporation or a tech support line, but his Mode 22 scan tool has kept more vintage GMs on the road than any dealership recall. Download it, connect it, and finally see what your old GM is really thinking.
Disclaimer: The GM Mode 22 Scan Tool by Terry is community-developed software. Always verify compatibility with your specific GM ECM/PCM mask ID and use at your own risk. Incorrect bi-directional commands can damage sensors or actuators. When in doubt, consult factory service manuals for your vehicle.
GM Mode 22 Scan Tool by Terry is a legacy, freeware diagnostic application designed to interface with General Motors vehicles through the OBD-II port. It is primarily recognized within automotive enthusiast communities for its ability to access manufacturer-specific data that standard generic scan tools often miss. Overview and Purpose Target Protocol : The tool focuses on
(Enhanced Data), which is a proprietary diagnostic mode used by General Motors to provide more detailed information than the standard legislated OBD-II Mode Functionality
: It allows users to request specific Parameter IDs (PIDs) from various vehicle control modules, including the Engine Control Module (ECM) and Transmission Control Module (TCM). Accessibility
: It was developed as a free alternative to expensive professional tools like the or modern GDS2 systems. Key Technical Capabilities Enhanced PID Access
: Unlike basic scanners that only show engine RPM or coolant temperature, this tool can potentially access "hidden" data such as transmission fluid temperature, actual boost levels, and detailed sensor voltages. Compatibility
: It typically requires an ELM327-based interface (often the USB version) to connect a laptop to the vehicle's 16-pin OBD-II port. Software Ecosystem
: It is often distributed alongside other classic OBD-II software like on technical repositories such as Limitations Technical Knowledge Required For owners and technicians working on 1980s to
: Users must often know or manually enter specific PID addresses and headers to retrieve data, as it does not always feature an automated interface for all GM models. Legacy Status
: As a piece of older freeware, it may struggle with modern GM "Global A" or "Global B" electrical architectures found in vehicles produced after 2010, which often require newer software like Techline Connect find specific GM PIDs for use with this tool, or are you looking for modern alternatives that run on mobile devices? OBD-II free software - OBDTester
GM Mode 22 Scan Tool by Terry: A Comprehensive Report
Introduction
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.
Overview of GM Mode 22 Scan Tool
The GM Mode 22 scan tool is a software-based tool that connects to a vehicle's onboard computer system, enabling technicians to diagnose and troubleshoot issues more efficiently. The tool is designed to work with GM vehicles and is compatible with a range of models, including those with CAN (Controller Area Network) and non-CAN bus systems.
Key Features of GM Mode 22 Scan Tool
Benefits of GM Mode 22 Scan Tool
Applications in the Automotive Industry
The GM Mode 22 scan tool has various applications in the automotive industry, including: “If you’re still trying to diagnose transmission or
Conclusion
The GM Mode 22 scan tool by Terry is a powerful diagnostic tool designed for GM vehicles. Its features, such as bi-directional control, real-time data streaming, and customizable interface, make it an essential tool for technicians. The tool's benefits, including improved diagnostic efficiency, enhanced accuracy, and increased productivity, make it a valuable asset for independent repair shops, dealerships, and fleet maintenance operations.
Recommendations
Based on the analysis, it is recommended that:
Future Developments
Future developments for the GM Mode 22 scan tool could include:
Overall, the GM Mode 22 scan tool by Terry is a valuable diagnostic tool that can help technicians and repair shops improve their efficiency and accuracy when working on GM vehicles.
The Terry GM Mode 22 Scan Tool has become a legendary piece of kit for enthusiasts of late-90s and early-2000s General Motors vehicles. Unlike generic code readers that only provide surface-level data, this specialized tool taps into the specific proprietary "Mode 22" diagnostics used by GM. If you are looking to diagnose a misfire, check real-time sensor data, or perform advanced maintenance on a classic LS-based engine or a 3800 Series V6, this tool is often the most cost-effective bridge between a basic scanner and a professional Tech 2.
The core appeal of Terry’s tool is its ability to access PID (Parameter ID) data that most budget scanners simply cannot see. Mode 22 is a specific request mode used by GM controllers to broadcast high-speed, live data. While a standard OBD-II scanner might show you a generic oxygen sensor reading, Terry’s setup allows you to monitor individual cylinder misfire counts, transmission line pressure, and torque converter slip in real-time. This level of granularity is essential for tracking down intermittent issues that don’t always trigger a Check Engine Light.
Setting up the scan tool typically requires a compatible interface cable and a laptop running the specific software developed and refined by the community. It is favored by the DIY crowd because it prioritizes function over form. The interface is lean and designed for performance, ensuring that data lag is minimized—a crucial factor when you are tuning a vehicle or trying to catch a momentary dip in fuel pressure.
One of the standout features often cited by users is the misfire monitor. GM’s Mode 22 data is famous for being incredibly sensitive. By using this tool, a mechanic can see if Cylinder 4 is having a slight "hiccup" even if the engine feels smooth to the touch. This allows for proactive maintenance, like replacing a single failing ignition coil or spark plug wire before it leaves you stranded or damages your catalytic converter.
Furthermore, the tool is a staple for those performing engine swaps. When putting a modern GM drivetrain into an older chassis, communication between the various control modules can be tricky. Terry’s tool helps verify that the PCM is receiving the correct signals from the rest of the vehicle, making it an indispensable part of the "LS swap" toolkit.
In a world where automotive software is increasingly locked behind subscriptions and expensive handheld units, the GM Mode 22 Scan Tool by Terry remains a testament to the power of community-driven diagnostics. It provides professional-grade insights for the price of a few parts, ensuring that older GM vehicles stay on the road and perform at their peak. Whether you are a weekend warrior or a dedicated tuner, having this tool in your garage changes the way you interact with your vehicle's computer.