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Heavy Duty Equipment Technician Red Seal Exam Prep · Question

A technician is diagnosing an intermittent communication fault on a 24V heavy-duty excavator's CAN bus system. Using an oscilloscope, they measure the voltage on the CAN-high line at 3.5V and the CAN-low line at 1.5V when communication is active. What is the differential voltage and does this indicate a healthy CAN bus signal?

The differential voltage on a CAN bus is the difference between CAN-high and CAN-low. Here, 3.5V - 1.5V = 2.0V. A differential voltage of approximately 2V and t

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Question: A technician is diagnosing an intermittent communication fault on a 24V heavy-duty excavator's CAN bus system. Using an oscilloscope, they measure the voltage on the CAN-high line at 3.5V and the CAN-low line at 1.5V when communication is active. What is the differential voltage and does this indicate a healthy CAN bus signal?

Answer options: ✅ Differential voltage is 2.0V; this indicates a healthy signal.

  • Differential voltage is 5.0V; this indicates a healthy signal.
  • Differential voltage is 2.0V; this indicates a fault in the CAN bus signal.
  • Differential voltage is 3.5V; this indicates a fault in the CAN bus signal.

Correct answer: Differential voltage is 2.0V; this indicates a healthy signal.

Explanation: The differential voltage on a CAN bus is the difference between CAN-high and CAN-low. Here, 3.5V - 1.5V = 2.0V. A differential voltage of approximately 2V and the specific voltage levels are characteristic of a healthy CAN bus signal (dominant state) in most heavy-duty applications as per OEM standards.

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