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Heavy Duty Equipment Technician Red Seal Exam Prep · Question

A heavy-duty truck equipped with a Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) system is experiencing frequent DPF regeneration cycles. Diagnostic trouble codes indicate a high soot load. Which of the following is the most likely contributing factor to this issue?

Operating a diesel engine predominantly at low loads and speeds results in lower exhaust temperatures, preventing passive regeneration and leading to increased

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Question: A heavy-duty truck equipped with a Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) system is experiencing frequent DPF regeneration cycles. Diagnostic trouble codes indicate a high soot load. Which of the following is the most likely contributing factor to this issue?

Answer options:

  • Low DEF (Diesel Exhaust Fluid) tank level. ✅ Operating the engine predominantly at low loads and speeds.
  • High quality, low sulfur diesel fuel usage.
  • Malfunctioning NOx sensor upstream of the SCR catalyst.

Correct answer: Operating the engine predominantly at low loads and speeds.

Explanation: Operating a diesel engine predominantly at low loads and speeds results in lower exhaust temperatures, preventing passive regeneration and leading to increased soot accumulation in the DPF, which then triggers more frequent active regeneration cycles.

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