Ensure your battery has at least 30% charge. Low voltage can cause the Diag port to be unstable.
Many SPD devices allow you to toggle DIAG mode through a hidden menu: Phone/Dialer Enter one of the following codes: *#*#83781#*#* *#*#9646633#*#* Navigate to the Connectivity USB Settings UART Settings and select How to Verify Connection To ensure you have entered the mode correctly: Right-click the Start button on Windows and select Device Manager Expand the Ports (COM & LPT) You should see an entry labeled SPD Diagnostic Port Unisoc USB Serial SCI USB2Serial (COMxx) Troubleshooting Tips enter diag mode spd