Final answer:
Using LS fuel in an engine designed for ULS can lead to the premature failure of the Diesel Particulate Filter (DPF) due to the higher sulfur content that can clog the filter or inhibit regeneration.
Step-by-step explanation:
When LS (low sulfur) fuel is used in an engine designed for ULS (ultra-low sulfur) fuel, the component most likely to fail first is the DPF (Diesel Particulate Filter). The DPF is especially sensitive to the sulfur content in the fuel because sulfur can form compounds that may clog the filter or inhibit its ability to regenerate. ULS fuels contain significantly lower amounts of sulfur, which helps in maintaining the functionality and longevity of the DPF by preventing these issues. If LS fuel is used instead, the higher sulfur content can lead to quicker degradation of the DPF, potentially causing it to fail before other components such as the C-EGR circuit, variable geometry turbocharger, or ECM heat exchanger.