Which exhaust colour indicates a dosing valve leak?

• A. Blue
• B. Brown
• C. Black
• D. White

Answer: (C)

Exhaust colour reflects what’s happening with fuel, air, and aftertreatment in the system. If a dosing valve leaks, it can dump excess fuel (or reducing agent) into the exhaust stream. That extra fuel isn’t fully burned in the engine, so soot particles form in the exhaust, resulting in dark, black smoke. So black exhaust is the telltale sign that a dosing valve is leaking. White smoke would point more to water/coolant issues, blue to oil burning, and doesn’t fit the symptom of a dosing valve leak.