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.
The GM Mode 22 Scan Tool by Terry is community-developed software. Always verify compatibility with your specific GM ECM/PCM mask ID and use at your own risk. Incorrect bi-directional commands can damage sensors or actuators. When in doubt, consult factory service manuals for your vehicle.
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.
While professional dealership tools like the GM Tech2 cost thousands of dollars, a developer known simply as released a free, lightweight software utility that could "talk" to GM vehicles using this specialized mode. The Story of a DIY Legend
In the early 2000s, accessing advanced data from a vehicle's computer typically required expensive professional equipment. The ELM327, a now-iconic integrated circuit, began to change this by providing a simple way to interface a computer with a car's OBD-II port. The “GM Mode 22 Scan Tool by Terry” was a direct beneficiary of this burgeoning hobbyist ecosystem. gm mode 22 scan tool by terry
It is listed among classic diagnostic tools for ELM327, such as OBD Logger by Jonathan Senkerik and pyOBD. Conclusion
“That’s the power of Mode 22,” says Terry. “Generic data would show RPM and VSS, but you’d never see the slip. You’d replace the torque converter unnecessarily.”
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:
Vehicle Diagnostic Scan Tool By BLUETOOTH... From 1,79 - DHgate Standard OBD-II protocols are designed for emissions testing
: 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
Here is everything you need to know about why this tool is a game-changer for GM diagnostics. What is "Mode 22"?
The GM Mode 22 Scan Tool by Terry: Specialized Functionality
To help you get the tool up and running or troubleshoot a specific vehicle issue, could you tell me: Always verify compatibility with your specific GM ECM/PCM
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.
: Specifically designed to request and display General Motors manufacturer-specific PIDs (Parameter IDs) that are not available through standard Mode 01 requests.
The tool records data at up to 8-10 frames per second (depending on cable speed). You can drive the car, log the run, and then review parameters like knock retard under load, TPS drop-out, or O2 sensor cross-counts—critical for tuning or finding intermittent misfires.
Vehicle diagnostics rely on specific "modes" of communication established by the Society of Automotive Engineers (SAE). While Mode $01 reads live powertrain data and Mode $03 reads standard trouble codes, is a proprietary diagnostic mode reserved by General Motors.