A heavy-duty transport truck operating in Ontario is fitted with a Diesel Oxidation Catalyst (DOC) and a Diesel Particulate Filter (DPF). The ECM logs a fault code indicating 'DPF Differential Pressure High'. Which of the following is the most likely cause?

Question: A heavy-duty transport truck operating in Ontario is fitted with a Diesel Oxidation Catalyst (DOC) and a Diesel Particulate Filter (DPF). The ECM logs a fault code indicating 'DPF Differential Pressure High'. Which of the following is the most likely cause?

Answer options: ✅ Excessive build-up of soot and ash in the DPF.

• An open circuit in the DPF differential pressure sensor wiring.
• A leak in the exhaust system upstream of the DPF.
• A faulty exhaust gas recirculation (EGR) valve stuck open.

Correct answer: Excessive build-up of soot and ash in the DPF.

Explanation: A high differential pressure across the DPF indicates that there's a significant restriction to exhaust gas flow within the filter. This is most commonly caused by an excessive build-up of soot that the DPF has not been able to regenerate effectively, or by excessive ash accumulation over time. The ECM monitors this pressure to determine the DPF's 'fullness' and trigger regeneration cycles. An open circuit would typically show unrealistic values or a specific sensor fault, and an exhaust leak would reduce differential pressure.