BUS-OFF state of system bus (CAN)

What does CE4 mean?

The controller has received too many faulty telegrams via the system bus (CAN) and has disconnected from the bus. This indicates a severe communication issue on the CAN network, preventing data exchange.

• Incorrect CAN bus termination resistor values (e.g., 60 Ohm or 180 Ohm instead of 120 Ohm) at bus ends.
• Severed or shorted CAN_H and CAN_L wires in the bus cable, often due to mechanical stress or sharp bends.
• Excessive network length (beyond 40m without repeaters) causing signal degradation and reflection issues.
• Electromagnetic interference (EMI) ingress on unshielded or improperly grounded CAN bus cables, leading to corrupt telegrams.
• Faulty CAN transceiver chip on one of the connected devices, transmitting corrupted data or failing to acknowledge.

Click steps to track your progress.

1. 1

   Measure the resistance across CAN_H and CAN_L terminals at each end of the bus (with power off) to verify 120 Ohm termination.

2. 2

   Inspect the entire CAN bus cable length for visible damage, sharp bends, or loose connections at each node's terminal block.

3. 3

   Using an oscilloscope, monitor CAN_H and CAN_L signal integrity at several points on the bus for proper differential signaling and absence of reflections.

4. 4

   Disconnect devices one by one to isolate a potential faulty node that is flooding the bus with error frames.

5. 5

   Verify ground connection integrity for all CAN bus nodes, ensuring a low impedance path to the common ground plane.

6. 6

   Check parameter C0004 (CAN baud rate) consistency across all connected devices and adjust if mismatched.