USB CAN Analyzer V8.00 causes CAN Bus A Off on 2009 GMC Sierra (Factory OBD-II)

General
1

Hello RealDash Team,

I am trying to connect a USB CAN Analyzer (V8.00) directly to the factory OBD-II port of my 2009 GMC Sierra (GM LS platform).

My wiring is:

  • OBD Pin 6 → CAN High
  • OBD Pin 14 → CAN Low
  • No 120Ω termination resistor enabled.
  • CAN bitrate: 500 kbps.

According to your forum, this direct connection should work with a CAN Analyzer, and I also found the GM LS XML files shared by RealDash. However, I am experiencing a serious issue.

As soon as I connect the CAN Analyzer to the vehicle CAN bus, the truck reports CAN communication faults, including traction/stability warnings, and a diagnostic scanner reports “CAN Communication Bus A Off”. Disconnecting the analyzer returns the network to normal.

I would like to ask:

  1. Has anyone successfully connected a USB CAN Analyzer directly to a factory GM/GMC OBD-II port without causing CAN Bus errors?
  2. Is there a recommended CAN Analyzer model that has been verified to work with RealDash on GM vehicles?
  3. Does the USB CAN Analyzer need to operate in a specific mode (such as Listen Only/Silent Mode) to avoid transmitting ACK or Error Frames?
  4. Have you seen similar issues with the common Chinese USB CAN Analyzer V8.00 adapters?

I would appreciate any advice or recommendations, as my goal is only to passively monitor the factory CAN bus and use the existing GM LS XML files in RealDash without transmitting any CAN messages.

Thank you for your support.