In standard OBD-II (SAE J1979), Mode 01 requests generic live data (RPM, coolant temp, speed). Mode 22 is a GM-specific proprietary mode (often called “High-Speed Data” or “Enhanced Parameters”).
It allows a scan tool to request individual Parameter IDs (PIDs) directly from a module at a much faster refresh rate than generic polling. This is critical for intermittent problems and dynamic drivetrain behavior. gm mode 22 scan tool by terry
Key Vehicles: Mode 22 is primarily found on GM vehicles from ~1996 to 2006 (pre-CAN bus transition), covering: In standard OBD-II (SAE J1979), Mode 01 requests
It displays sensor readings in real-time, updating several times per second. This allows you to watch how sensors respond to throttle changes, engine load, and temperature shifts—critical for diagnosing intermittent issues. Limitations: Newer Global A vehicles (2014+) require Mode
Limitations: Newer Global A vehicles (2014+) require Mode 23 or GMLAN-enhanced protocols – not supported.
Unlike modern generic scan tools that use a standard J1850 or CAN bus, Terry’s tool sends a specific Mode 22 request frame to the ECM. The ECM responds by dumping a packet of 32–64 bytes of raw RAM data. Terry’s software then decodes that raw hex data into human-readable values.
Why is this a big deal? Because the "Terry" interpretation accounts for the unique scaling and addressing used by each GM ECM. A generic tool might just display "MAF = 127," but Terry’s tool knows that raw value of 127 actually means 12.7 grams/second. That level of specific calibration is why enthusiasts still seek out this tool.
