To understand why Terry's software is valuable, it is crucial to understand how On-Board Diagnostics (OBD) systems handle data request requests. Generic OBD-II vs. Manufacturer-Specific Diagnostics
What (like an OBDLink or ELM327) do you plan to use?
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
| 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 |
[Vehicle OBD-II Port] ---> [ELM327 or OBD2crazy Serial Cable] ---> [PC running Terry's Scan Tool] All Car Diagnostic Tools - Snap-on gm mode 22 scan tool by terry
Unlike pulling trouble codes, which only tell you that something is wrong, this tool tells you what is wrong. You can observe the oxygen sensor oscillating to see if the engine is running rich or lean, or check if the TPS is showing a smooth transition from idle to wide-open throttle. 2. Deep Diagnostics (BLM and Integrator)
Standard OBD-II protocols are designed for emissions testing and basic engine data. However, manufacturers like GM and Ford use to transmit more detailed information through the CAN network.
A high-quality OBD2 adapter is required. While cheap ELM327 clones sometimes work, adapters featuring original STN1110 or PIC18F25K80 chips (such as the OBDLink LX/MX series) offer the timing stability required for custom hex commands.
Because these codes are proprietary, they are often guarded by manufacturers or sold for high fees. Terry's scan tool was developed to give enthusiasts a way to request this data without needing expensive dealership equipment like the GM MDI 2 . Why Use the "Terry" Version? To understand why Terry's software is valuable, it
Mode 22 is primarily found on GM vehicles from ~1996 to 2006 (pre-CAN bus transition), covering:
The is a lightweight, legacy software utility designed to work with ELM327-based interfaces. Free USB OBDII software - MoneySavingExpert Forum
Mode $22 allows a scan tool to request specific data parameters (PIDs) directly from individual electronic control modules (ECUs). This includes data from the: Powertrain Control Module (PCM) Transmission Control Module (TCM) Body Control Module (BCM) Electronic Brake Control Module (EBCM/ABS)
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 , becomes indispensable. GM Mode 22 Scan Tool by Terry is
If you have a modern computer architecture or find Terry's legacy terminal utility too manual, several alternatives offer alternative or upgraded options:
This comprehensive guide covers the significance of GM Mode 22, the role played by Terry's software, and how it laid the framework for modern diagnostic applications. What is OBD-II Mode 22?
Body Control Module (BCM) inputs like door switches and lighting states Fuel trim data per cylinder Knock sensor activity in real-time Origin of "Terry's" Custom Tool
A flashing check engine light indicates a severe misfire, but generic codes (like P0300) often label it as a random or multiple cylinder misfire. Terry’s tool leverages Mode 22 to view real-time, individual misfire counters for cylinders 1 through 8. This lets you spot a single failing spark plug wire or valve spring before it triggers a hard fault code. 4. Raw Sensor Voltages