An excavator operating on a remote site in Quebec has an engine with a modern Tier 4 diesel engine featuring an electronic control module (ECM). The operator reports intermittent dashboard warnings and a 'limp mode' activation. The diagnostic tool shows multiple 'U' series Diagnostic Trouble Codes (DTCs), specifically U0073 (Control Module Communication Bus Off). Which component should the technician inspect first?

Question: An excavator operating on a remote site in Quebec has an engine with a modern Tier 4 diesel engine featuring an electronic control module (ECM). The operator reports intermittent dashboard warnings and a 'limp mode' activation. The diagnostic tool shows multiple 'U' series Diagnostic Trouble Codes (DTCs), specifically U0073 (Control Module Communication Bus Off). Which component should the technician inspect first?

Answer options: ✅ The CAN bus terminating resistors.

• The fuel pressure sensor wiring.
• The engine oil level switch.
• The turbocharger wastegate actuator.

Correct answer: The CAN bus terminating resistors.

Explanation: U-series DTCs, particularly U0073 ('Control Module Communication Bus Off'), are directly related to CAN bus communication issues. Terminating resistors are crucial for CAN bus signal integrity, preventing reflections and ensuring proper communication between electronic control units (ECUs), making them a primary suspect.