CAN Bus-Off State

What does ce4 mean?

The controller has entered a 'Bus-Off' state, meaning it has detected and received too many faulty telegrams on the system bus and has consequently disconnected itself. This indicates severe bus communication issues, such as incorrect termination, poor shielding, or excessive bus load. Being 'Bus-Off' means the controller cannot communicate, halting operations.

• Persistent high error rate on the CAN bus due to repeated data corruption or arbitration losses.
• Incorrect bus termination (e.g., missing 120 Ohm resistors, multiple terminators) causing signal reflections.
• Short circuit between CAN_H and CAN_L lines, or either line to ground/supply, on the CAN bus.
• Defective CAN transceiver chip on the controller or another device on the network.
• Excessive network length or improper cable impedance leading to significant signal degradation.

Click steps to track your progress.

1. 1

   Disconnect all devices from the CAN bus except for the controller and one other known-good device, then re-establish communication.

2. 2

   Measure the resistance across the CAN_H and CAN_L lines; it should be approximately 60 Ohms with two 120 Ohm terminators or 120 Ohms with a single terminator.

3. 3

   Systematically check each segment of the CAN bus cable for short circuits between CAN_H, CAN_L, and ground using a multimeter.

4. 4

   Verify all CAN devices on the network are configured with unique node IDs (e.g., P8-02 for CAN-IN1, P8-12 for CAN-IN2) and identical baud rates (P8-01 or P8-11).

5. 5

   Inspect the CAN bus cable for correct impedance (typically 120 Ohms) and maximum length specifications for the given baud rate.