Right-click the device > Properties > Port Settings > Advanced. Change the COM port number to COM 3, 4, or 5 (Opcom 1.39 prefers low numbers). Also set Latency Timer to "1" (very important for stable data).
In the world of automotive diagnostics, the balance between professional-grade functionality and affordability is a tightrope walk. For owners of General Motors (GM) vehicles—specifically Opel, Vauxhall, and Holden—one name has echoed through forums, garage meet-ups, and DIY repair blogs for over a decade: Opcom . opcom free4all portable
Do not install the software via MSI. Simply double-click Opcom_Portable.exe or Run.bat . The software should open immediately. Right-click the device > Properties > Port Settings
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