The GM Mode 22 Scan Tool, developed by Terry (often associated with the "Scan Tool by Terry" or "STBT" project), represents a significant milestone in the world of DIY automotive diagnostics. While professional-grade scanners often cost thousands of dollars, this tool was designed to provide enthusiasts and home mechanics with deep-level access to General Motors vehicle data using affordable hardware. The Power of Mode 22
In the world of OBD-II diagnostics, most basic scanners rely on "Mode 01" data, which is the federally mandated generic information required for emissions testing. This includes basic engine RPM, coolant temperature, and oxygen sensor readings. However, GM vehicles utilize Mode 22, a proprietary diagnostic mode that allows for "Enhanced Data."
Mode 22 provides access to specific Parameter IDs (PIDs) that generic scanners cannot see. This includes critical transmission data (like fluid temperature and gear slip), individual wheel speed sensors for ABS troubleshooting, fuel trim data for specific engine banks, and oil life monitoring. By targeting Mode 22, Terry’s tool unlocked professional-level insights for the average user. Accessibility and Community Impact
What makes the "Scan Tool by Terry" notable is its focus on accessibility. In an era where automotive software is increasingly locked behind subscriptions and expensive proprietary interfaces, this project offered a way to interface with GM’s complex Electronic Control Units (ECUs) using standard laptops and inexpensive interface cables.
The tool became a staple in online enthusiast communities. It allowed owners of classic GM platforms—such as the LS-based trucks, Corvettes, and late-model Pontiacs—to perform their own tuning, troubleshoot intermittent electrical ghosts, and verify the health of their drivetrains without a trip to the dealership. Technical Simplicity
The genius of the tool lies in its efficiency. Rather than a bloated graphical user interface, the tool focuses on the raw exchange of data. It interprets the hexadecimal responses from the vehicle's computer and translates them into human-readable values. This lightweight approach ensured that the software could run on older hardware, making it a rugged choice for a garage environment where high-end computers might be at risk. Conclusion gm mode 22 scan tool by terry
The GM Mode 22 Scan Tool by Terry serves as a testament to the power of the automotive hobbyist community. It bridged the gap between expensive professional equipment and the limited functionality of generic code readers. By democratizing access to manufacturer-specific data, it empowered thousands of vehicle owners to better understand, maintain, and enjoy their GM vehicles.
Should we look into the hardware requirements needed to run this software, or
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. The GM Mode 22 Scan Tool , developed
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: Fuel pump relay on/off (prime the system without
Bluetooth V1.5 V2.1 ELM 327 WIFI/WI-FI V1.5 OBDII ... - eBay
This is where Terry’s tool beats any generic scanner. You can command:
| Tool | Mode 22 Support | Price | Ease of Use | |------|----------------|-------|--------------| | Terry’s Tool | Yes (older GM) | Free | Moderate (requires PC) | | Tech 2 | Full | $500–2000 | High | | Autel MaxiDiag | Partial (some PIDs) | $500+ | High | | Torque Pro + custom PIDs | Limited (requires manual PID entry) | $5 | Medium |
Problem: 1994 C4 Corvette idles rough but no OBD-II codes. Solution: Use Mode 22 to view the IAC position and TPS closed-throttle voltage. The tool reveals a TPS voltage of 0.78V (spec is 0.45-0.65V) – adjusting the TPS fixes the idle.
Problem: 1991 Camaro 5.7L TPI has hesitation under load. Solution: Log Mode 22 data during a test drive. The log shows the knock sensor pulling 8-10° of timing at 2500 RPM, but there is no audible knock. Replace the knock sensor (false triggering due to a loose torque converter bolt).
Problem: 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.