What color is used to denote a DEF fill cap?

The color blue is used to denote a Diesel Exhaust Fluid (DEF) fill cap. This color standardization helps to easily identify the filling point for DEF, which is crucial in diesel engines equipped with selective catalytic reduction (SCR) systems to reduce emissions. Using a distinct color like blue ensures that technicians and vehicle operators can quickly recognize the fill cap among other fluid caps, minimizing the risk of cross-contamination with other fluids, such as diesel fuel or coolant. Proper identification of the DEF cap is important for vehicle maintenance and environmental compliance, as using the incorrect fluid can lead to serious engine damage and increased emissions.