Gm Mode 22 Scan Tool By Terry -

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).

Terry’s original tool was written for Windows 95/98/XP. However, modern versions or community updates run on Windows 10/11 in compatibility mode. Install the FTDI or Prolific drivers for your USB-to-serial adapter.

| Tool | Protocol | Price | Best For | |------|----------|-------|-----------| | | ALDL Mode 22 | Free | Budget, simple diagnostics | | Scan9495 | ALDL Mode 22 | $30 shareware | LT1/LT4 specific (94-95) | | TunerPro RT | ALDL + OBD-II | Free (donation) | Advanced tuning & logging | | ALDLLogger | ALDL Mode 22 | Free | Mac/Linux users | | Tech 1 w/ GM cartridge | All GM modes | $500+ used | Professional restoration | gm mode 22 scan tool by terry

For decades, General Motors vehicles (GM, Chevrolet, Buick, Cadillac, Pontiac, Oldsmobile, GMC) have relied on a unique and powerful data stream known as Mode 22 . While generic OBD-II scanners can read basic engine codes and live data on vehicles from 1996 onward, older GM models (primarily 1980–1995) and even some early OBD-II systems speak a different language. Enter the legendary solution: The GM Mode 22 Scan Tool by Terry .

Find the 12-pin connector. On most F-bodies and Corvettes, it is under the dash left of the steering column. On trucks, it may be above the gas pedal. 1991 Camaro 5

For the price of a USB ALDL cable (around $40-60), you can have dealer-level diagnostics from the early 1990s. Terry may not have a corporation or a tech support line, but his Mode 22 scan tool has kept more vintage GMs on the road than any dealership recall. Download it, connect it, and finally see what your old GM is really thinking. 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.

Turn the ignition to ON (engine off for sensor checks) or start the engine. Click “Connect” or “Scan Mode 22”. Replace the knock sensor (false triggering due to

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.