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-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. gm mode 22 scan tool by terry
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 legacy freeware commonly bundled with ELM327 OBD-II interfaces for reading enhanced GM-specific diagnostics. Designed for older operating systems, it provides access to specialized vehicle data parameters not available in standard generic OBD-II modes. For modern GM vehicles, users typically transition to factory-level tools like the OEMTools GM MDI or advanced third-party scanners. Interfuse LLC. Obd2 elm327 v1.5 usb can bus scanner | PDF - Slideshare
Early versions were DOS or early Windows based, but more refined versions (often packaged as "TTS DataMaster" or similar, with Terry’s foundational logic) include the ability to log data to a file and play it back. This allows you to drive the car, record a stumble or misfire, and then review the data frame-by-frame later.
View every analog and digital input the ECM sees:
“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.”
GM Mode 22 Scan Tool by Terry is a legacy, free software utility designed for diagnosing General Motors vehicles. It primarily serves as an interpreter for "Mode 22" (also known as Mode $22), a proprietary diagnostic mode used by GM to provide enhanced sensor data that standard OBD-II protocols do not typically reveal. Core Functionality Enhanced Data Retrieval GM Mode 22 Scan Tool by Terry is
: Unlike generic OBD-II modes (like Mode 01), which only provide legally mandated emissions data, Mode 22 allows the user to request manufacturer-specific Parameter IDs (PIDs) Live Sensor Monitoring : It can display real-time data such as Engine RPM Coolant Temperature Vehicle Speed Fuel System Status Compatibility : The software is specifically designed to work with
based USB interfaces. It is widely listed as part of free software bundles provided with affordable OBD-II scanners. Quadstar Tuning LLC Historical Context OBD-II free software - OBDTester
In the world of GM tuning and diagnostics, “Terry” is a whispered name of respect. While multiple developers have created Mode 22 interfaces, the version most widely known as “the Terry tool” or “Terry’s Mode 22 Scanner” originated from the early 2000s GM EFI tuning forums (like thirdgen.org, DIY-EFI, and Gearhead-EFI).
Terry was a community programmer who recognized that professional tools like the Tech 1 or Vetronix Mastertech were expensive, rare, and locked to dealer use. He developed a software-based solution—often distributed as a freeware/shareware Windows application—that, when paired with a simple serial or USB-to-ALDL cable, could perform miracles. His tool demystified the $EE, $8D, $42, and $58 masks used in GM vehicles from the mid-80s to the mid-90s.
Key Models That Benefit from Terry’s Mode 22 Tool:
1. The "Terry Tune-Up" Presets Since the tool is "By Terry," it should leverage his specific diagnostic expertise. The feature would include pre-programmed test routines found in his tutorials:
2. GM-Specific Wizardry (Mode 22 Deep Dive) This feature would decode the obscure Mode 22 data that generic OBD2 tools miss.
3. Automated "Scope" Triggers Connect a cheap USB scope or use high-speed data logging.
The GM Mode 22 Scan Tool by Terry is a classic example of enthusiast-driven engineering filling a gap where commercial tools were either too expensive or nonexistent. While it lacks the polish and speed of a $10,000 Tech 2 or modern aftermarket scanner, it provides exactly the data needed to correctly diagnose fuel, ignition, and sensor issues on vintage GM EFI systems.
For anyone restoring a C4 Corvette, a 3rd-gen Camaro, a GMT400 pickup, or a Buick Grand National, this tool is a must-have. It turns guesswork into data, and data into a running, driving classic.
Disclaimer: The original author "Terry" (full identity and version lineage vary across forums) released this tool as freeware for personal use. Always verify compatibility with your specific ECM ID before use.
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 Support : The tool supports Mode
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."
Best for:
Limitations: Newer Global A vehicles (2014+) require Mode 23 or GMLAN-enhanced protocols – not supported.