Heavy Duty Equipment Technician Red Seal Exam Prep · Question
A new heavy-duty grader occasionally experiences engine derating and fault codes related to 'CAN Bus Data Missing from Transmission Control Unit (TCU)'. The technician inspects the wiring and connector at the TCU and central gateway module, finding no obvious damage. Which of the following is the next logical step in diagnosing this intermittent CAN bus issue?
Intermittent fault codes and derating, especially when no obvious damage is found, often point to a poor connection. A 'wiggle test' involves gently manipulatin
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Question: A new heavy-duty grader occasionally experiences engine derating and fault codes related to 'CAN Bus Data Missing from Transmission Control Unit (TCU)'. The technician inspects the wiring and connector at the TCU and central gateway module, finding no obvious damage. Which of the following is the next logical step in diagnosing this intermittent CAN bus issue?
Answer options:
- Replace the Engine Control Unit (ECU) immediately.
- Check the power and ground supply to the TCU. ✅ Perform a wiggle test on the entire CAN bus harness while monitoring communication.
- Reroute all CAN bus wiring away from other electrical harnesses.
Correct answer: Perform a wiggle test on the entire CAN bus harness while monitoring communication.
Explanation: Intermittent fault codes and derating, especially when no obvious damage is found, often point to a poor connection. A 'wiggle test' involves gently manipulating wiring harnesses and connectors while monitoring for changes in communication status using a diagnostic tool. This can reveal intermittent breaks or shorts within the harness that are not visible during a static inspection. Replacing the ECU or rerouting wiring are premature steps. Checking power and ground to the TCU is important, but a wiggle test specifically targets communication integrity over the entire bus.
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