A technician is diagnosing an intermittent communication fault on a heavy-duty excavator's CAN bus system. Using an oscilloscope, they observe that the CAN High and CAN Low signals are consistently at 2.5 V when idle, but during communication, the CAN High signal fluctuates between 2.5 V and 3.5 V, and CAN Low fluctuates between 2.5 V and 1.5 V. What does this indicate about the CAN bus termination?

Question: A technician is diagnosing an intermittent communication fault on a heavy-duty excavator's CAN bus system. Using an oscilloscope, they observe that the CAN High and CAN Low signals are consistently at 2.5 V when idle, but during communication, the CAN High signal fluctuates between 2.5 V and 3.5 V, and CAN Low fluctuates between 2.5 V and 1.5 V. What does this indicate about the CAN bus termination?

Answer options: ✅ The CAN bus is properly terminated.

• The CAN bus has too many termination resistors.
• The CAN bus is missing one or both termination resistors.
• There is a short circuit on the CAN bus lines.

Correct answer: The CAN bus is properly terminated.

Explanation: The observed voltage fluctuations (CAN High: 2.5V-3.5V and CAN Low: 2.5V-1.5V) with a differential voltage of approximately 2V during data transmission are characteristic of a correctly terminated and functioning CAN bus system. If there were issues with termination resistors, the voltage levels and signal integrity would be significantly compromised, often showing reflections or incorrect DC offset voltages. Too many termination resistors or missing resistors would distort these voltage levels drastically.