LED on the COM Port of the USB-8502 Turning Red

Updated Mar 27, 2023

Reported In


  • USB-8502

Issue Details

I am trying to read CAN frames from my network and the LED on the COM port of my USB-8502 device turns red quickly after it starts trying to read frames. What does the red LED mean?


If the LED on your USB-8502 turns red, this means your device has entered the "Bus OFF State" and will stop trying to read frames from the CAN network. The USB-8502 will enter this state when it reads a long stretch of continuous error frames. 

Additional Information

Common reasons this occurs:
  • The baud rate setting for your device is not set to the same baud rate as your network.
  • The devices on your network are not actually sending frames that follow the CAN/J1939 protocol.
  • The CAN cables in your network are not properly terminated.
  • There is a physical layer mismatch between the USB-8502 and the network you are connected with.