The "Failed to create diag service" error indicates that the QXDM application on your PC could not successfully instantiate the communication channel required to talk to this subsystem. This failure can occur at various levels: the physical layer (USB/Cable), the driver layer (Windows OS), the service layer (Qualcomm Drivers), or the application layer (QXDM configuration).
: brltty service claims all Qualcomm DIAG interfaces. Fix : sudo apt remove brltty and add udev rule: SUBSYSTEM=="tty", ATTRSinterface=="Qualcomm Diagnostics", MODE="0666" qxdm failed to create diag service
: Build config USB_CONFIG_INCLUDE_DIAG=0 in NvItem Fix : Override NV 6468 (USB configuration) using QMSL_WriteNV() to enable diag interface. The "Failed to create diag service" error indicates
Many production devices (non-engineering samples) have the DIAG port disabled at the kernel or Android level. You may need to enable it via one of these methods: Fix : sudo apt remove brltty and add
When QXDM on your Windows PC tries to connect to the device via a COM port (or USB), it sends a handshake request. If the device either: