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.
Terry’s tutorials are famous for teaching people how to fix specific GM problems using affordable tools.
“If you own a 1998–2013 GM truck and want to see exactly what your ECM, TCM, and ABS module are doing – without spending $1,000 on a Tech 2 – Terry’s Mode 22 tool is a must-have. It’s not pretty, but it works.”
Unlocking the Power of the GM Mode 22 Scan Tool: A Deep Dive into Terry’s Custom Solution
For GM enthusiasts, DIY mechanics, and LS-swap aficionados, the term "Mode 22" holds a special kind of reverence. While standard OBDII protocols give you the basics—like engine RPM, coolant temp, and those dreaded P0420 codes—they barely scratch the surface of what a General Motors Engine Control Module (ECM) actually knows.
Enter the GM Mode 22 Scan Tool by Terry. This specialized tool has gained a cult following in automotive forums and tuning circles for its ability to bridge the gap between basic consumer scanners and thousand-dollar professional diagnostic suites.
Here is everything you need to know about why this tool is a game-changer for GM diagnostics. What is "Mode 22"?
Before diving into the tool itself, it’s important to understand the protocol. Standard OBDII diagnostics use "Modes" (like Mode 01 for live data and Mode 03 for stored codes). These are federally mandated and universal across all brands.
Mode 22, however, is a proprietary GM diagnostic service. It allows for "Read Data by Identifier" (DID). In plain English: it lets you request specific, high-resolution data parameters that aren't available on standard scanners. We’re talking about granular transmission pressures, individual wheel speed sensor data, injector pulse widths, and knock sensor activity that standard tools often miss or lag on. The Man Behind the Tool: Who is Terry?
In the world of automotive electronics, some of the best tools come from independent developers who are frustrated by the limitations of commercial products. "Terry" (often associated with specialized software interfaces and hardware loops for older GM platforms) developed this tool to provide a lightweight, lightning-fast way to pull proprietary data without the overhead of a massive "all-in-one" scanner. Key Features of the GM Mode 22 Scan Tool
The reason this specific tool pops up in so many LS-swap and Silverado forums is its focus on utility over fluff.
High Refresh Rates: Standard OBDII data can be "laggy." Terry’s Mode 22 tool optimizes the request-response cycle, giving you near real-time data which is critical for diagnosing intermittent misfires or tuning fuel maps.
Extended Parameter IDs (PIDs): It unlocks access to PIDs like "Oil Pressure" (which many GM trucks don't report over standard OBDII), "Transmission Fluid Temp," and "Desired vs. Actual Idle."
Bi-Directional Light: While primarily a data logger, certain versions of these custom Mode 22 scripts allow for basic "active tests," such as cycling a cooling fan or testing an EVAP solenoid.
Hardware Compatibility: It is designed to work with affordable interfaces (like the OBDLink MX+ or specialized USB-to-OBD cables), making professional-level data accessible for the price of a few tanks of gas. Why You Need It for Tuning and Troubleshooting
If you are running a 4.8, 5.3, or 6.0 Vortec engine, or a classic LS1/LS6, the GM Mode 22 Scan Tool is your best friend for two specific scenarios:
Diagnosing "Ghost" Issues: Ever have a truck that stumbles but doesn't throw a code? Standard scanners might show a "green light," but Mode 22 can show you that your Long Term Fuel Trims are drifting or that a specific sensor is reporting "noise" just outside the standard threshold.
LS Swaps: When you put a modern GM engine into an old C10 or a Jeep, getting the gauges to talk to the computer is a nightmare. Terry’s tool helps verify that the ECU is seeing the correct inputs before you spend hours wiring up physical gauges. How to Get Started
Using the GM Mode 22 Scan Tool usually involves a specific hardware-software combo. Most users pair a laptop or an Android device with a high-quality OBD interface. Unlike "plug-and-play" tools from big-box stores, you may need to load specific PID lists or configuration files provided by Terry to "unlock" the full potential of your specific VIN. Final Verdict
The GM Mode 22 Scan Tool by Terry isn't for the person who just wants to turn off a gas cap light. It is a precision instrument for the "garage scientist." It provides a window into the brain of your GM vehicle that was previously reserved for dealership technicians with Tech2 scanners.
If you’re serious about maintaining, tuning, or reviving a GM vehicle, this tool is one of the most cost-effective performance upgrades you can "install."
The GM Mode 22 Scan Tool by Terry is a legacy freeware diagnostic software primarily used with ELM327-based adapters to interface with General Motors vehicles. Its core purpose is to leverage GM-specific Mode 22 diagnostics, which allow access to a deeper range of sensor data than standard OBD-II protocols. Key Features
Mode 22 Support: Specifically designed to request and display General Motors manufacturer-specific PIDs (Parameter IDs) that are not available through standard Mode 01 requests.
Freeware Availability: Distributed as a free software utility for Windows-based PCs, making it a budget-friendly option for DIY enthusiasts. gm mode 22 scan tool by terry
Live Data Streaming: Allows users to monitor vehicle performance in real-time by reading raw data directly from the ECU.
DTC Management: Capable of reading and clearing diagnostic trouble codes (DTCs) to help identify and reset check engine lights.
Hardware Compatibility: Works with standard ELM327 OBD-II interfaces, including USB and Bluetooth variants.
Platform Support: Traditionally compatible with older Windows operating systems such as Windows 98, 2000, and XP. Modern Alternatives for GM Vehicles
For users with newer GM models (2010+), modern tools often provide more comprehensive "dealer-level" capabilities:
Bluetooth V1.5 V2.1 ELM 327 WIFI/WI-FI V1.5 OBDII ... - eBay
In-Depth Review of GM Mode 22 Scan Tool by Terry
The GM Mode 22 scan tool, developed by Terry, is a software-based diagnostic tool designed to interface with General Motors vehicles. This review aims to provide an exhaustive analysis of the tool's capabilities, features, and performance.
Overview
The GM Mode 22 scan tool is a Windows-based application that allows users to connect to a vehicle's onboard computer (ECU) via a compatible OBD-II interface. The tool provides access to various vehicle parameters, enabling users to diagnose and troubleshoot issues, as well as perform advanced functions.
Key Features
User Interface and Experience
The GM Mode 22 scan tool features a user-friendly interface, with a logical and intuitive layout. The main dashboard provides quick access to essential functions, while the menu system allows users to navigate to more advanced features.
Performance and Compatibility
The GM Mode 22 scan tool performed well during testing, with reliable connections and accurate data readings.
Comparison to Other Scan Tools
The GM Mode 22 scan tool stands out from other scan tools on the market due to its:
Conclusion
The GM Mode 22 scan tool by Terry is a powerful and versatile diagnostic tool designed for General Motors vehicles. Its advanced features, user-friendly interface, and reliable performance make it an excellent choice for DIYers and professionals.
Rating: 4.5/5
Recommendation:
The GM Mode 22 scan tool is recommended for:
Limitations:
Future Development:
The developer, Terry, has expressed plans to continue updating and improving the GM Mode 22 scan tool. Future updates may include:
Overall, the GM Mode 22 scan tool by Terry is a valuable resource for anyone working on General Motors vehicles. Its advanced features and reliable performance make it a worthwhile investment for DIYers and professionals alike.
GM Mode 22 Scan Tool by Terry is a free, legacy diagnostic software utility designed for use with ELM327-based hardware interfaces
to access enhanced diagnostic data from General Motors vehicles. Key Features and Capabilities
This tool specializes in proprietary GM diagnostic "Mode 22" requests, which provide deeper insight than standard generic OBD-II modes. Its primary functions include: Enhanced Data Access
: Reads ongoing sensor data and fault codes beyond basic emissions-related info, allowing users to view real-time data while driving. Sensor Monitoring : Displays a variety of parameters including: Engine RPM and Vehicle Speed. Coolant and Intake Air Temperatures. Fuel System Status and Fuel Pressure. Short/Long Term Fuel Trims. Timing Advance and Air Flow Rate. Absolute Throttle Position. Code Management
: Allows users to read and clear diagnostic trouble codes (DTCs) and reset the Check Engine Light (MIL). Technical Details Hardware Requirement
: Typically requires an ELM327 USB or Bluetooth interface to bridge the vehicle's computer and a PC. Software Design
: It was originally distributed as a lightweight, user-friendly program. Installation usually involves simply extracting files to a hard drive folder without a complex installer. Availability
: It is often found in the "downloads" or "free software" sections of OBD diagnostic resource sites
In the mid-2000s, the "GM Mode 22 Scan Tool by Terry" was a small but legendary piece of the early OBD-II hobbyist scene. At the time, General Motors used a proprietary diagnostic method called Mode 22, which allowed for deeper data extraction than the standard OBD-II protocols required by law.
While professional dealership tools like the GM Tech2 cost thousands of dollars, a developer known simply as Terry released a free, lightweight software utility that could "talk" to GM vehicles using this specialized mode. The Story of a DIY Legend
Terry’s tool was born out of the "Wild West" era of car hacking. During this time, enthusiasts were transitioning from the old ALDL systems of the '80s to the more complex computer networks of modern vehicles.
The Problem: Standard scanners could only see "Generic" data like engine RPM or basic trouble codes. To see "Enhanced" data—like individual wheel speeds for ABS or transmission oil temperature—you needed a tool that understood GM's proprietary Mode $22.
Terry's Solution: Terry wrote a program that ran on simple PC-based interfaces (like the ELM327). It was one of the first times a regular car owner could plug in a cheap laptop and see the same high-level data a dealership mechanic saw.
The Legacy: Terry's tool became a staple on forums like Scantool.net and early car-tuning communities. It paved the way for modern, affordable bi-directional scanners from brands like Launch and Autel that we use today.
Though largely superseded by modern apps and GDS2 software, "GM Mode 22 Scan Tool by Terry" remains a nostalgic name for anyone who spent their weekends in a garage with a bulky laptop and a dream of fixing their own Chevy or Buick.
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. Understanding the GM Mode 22 Scan Tool by
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:
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.
Based on the existing reputation of "Terry" (likely Terry Johnson of Terry's GM Tutorials) 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."
Here is a detailed proposal for that feature:
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.
Mode 22 refers to a specific command request within that proprietary ALDL protocol. Unlike “Mode 1” (basic OBD-II generic data), Mode 22 allows a scan tool to request any memory address within the computer’s RAM or ROM. This means you can access:
Most generic code readers cannot send Mode 22 requests. They are locked into universal OBD-II PIDs (Parameter IDs). This is where a dedicated tool, specifically The GM Mode 22 Scan Tool by Terry, becomes indispensable.
Once you have the software and cable, follow this guide:
Step 1 – Locate the ALDL Port: Find the 12-pin connector. On most F-bodies and Corvettes, it is under the dash left of the steering column. On trucks, it may be above the gas pedal.
Step 2 – Connect the Cable: 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.
Step 3 – Install Drivers (Windows only): 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.
Step 4 – Launch the Software: Open “GM Mode 22 Scanner by Terry.exe”. Set the correct COM port and baud rate (8192).
Step 5 – Power Cycle: Turn the ignition to ON (engine off for sensor checks) or start the engine. Click “Connect” or “Scan Mode 22”.
Step 6 – Interpret Data: The software will populate fields. Pay special attention to: The Gap: Most affordable tools show what is
Pros:
Cons: