Heavy Duty Equipment Technician Red Seal Exam Prep · Question
A forestry feller buncher's diagnostic tool indicates a 'CAN Bus off-line' error, affecting communication between the engine ECM and the transmission ECM. Further investigation reveals that the CAN bus communication wires (CAN-High and CAN-Low) are showing a continuous short to ground on an oscilloscope. What is the most likely cause?
A continuous short to ground on both CAN-High and CAN-Low lines would completely disable communication, indicating a severe physical fault. This is most commonl
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Question: A forestry feller buncher's diagnostic tool indicates a 'CAN Bus off-line' error, affecting communication between the engine ECM and the transmission ECM. Further investigation reveals that the CAN bus communication wires (CAN-High and CAN-Low) are showing a continuous short to ground on an oscilloscope. What is the most likely cause?
Answer options: ✅ A direct short circuit in the CAN bus wiring harness due to chafing or damage.
- An open circuit in an individual CAN node's internal transceiver.
- An excessive number of active nodes on the CAN network, causing overload.
- Incorrect termination resistor values present on the bus.
Correct answer: A direct short circuit in the CAN bus wiring harness due to chafing or damage.
Explanation: A continuous short to ground on both CAN-High and CAN-Low lines would completely disable communication, indicating a severe physical fault. This is most commonly caused by damaged wiring (chafing against a frame, pinching), leading to the wires making contact with the vehicle's chassis or ground, which directly shorts out the differential signal.
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