USB‑8502 Enters Bus OFF State and LED Turns Red

Issue Details

USB‑8502 Enters Bus OFF State and LED Turns Red

When using an NI USB‑8502, the device LED turns red, and the device enters a Bus OFF state. When this occurs, the device cannot communicate on the CAN network and does not function as expected.

Solution

This behavior typically occurs after a long sequence of CAN errors or when Windows USB power management settings interrupt communication with the device.

You can recover the USB‑8502 from the Bus OFF state by performing a Self-Test using the methods below.

• Perform a Self-Test Using NI MAX

1. 1. Connect the USB‑8502 directly to the computer.
   2. Open NI Measurement & Automation Explorer (NI MAX).
   3. Expand Devices and Interfaces.
   4. Right-click the USB‑8502.
   5. Select Self-Test.
   6. Verify that the self-test completes successfully.

• If you need to perform the recovery programmatically, you can use the Self-Test VI in LabVIEW.

1. 1. Open LabVIEW.
   2. Navigate to
      Measurement I/O » System Configuration » Hardware Management » Self-Test.
   3. Use the Self-Test VI to initiate a self-test on the USB‑8502.
   4. Run the VI and monitor for a successful completion.

An example demonstrating this functionality is available in LabVIEW:

1. In LabVIEW, select Help » Find Examples.
2. Set Browse according to: to Directory Structure.
3. Open the nisyscfg folder.
4. Locate and open Self-Test All Devices.vi.

If the self-test passes, check whether the device LED returns to its normal state and communication resumes.

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.

If you follow all the steps above, and the issue still persists, then please contact NI Support as the device might be in need of repair.