What exhaust smoke color indicates a leaking "Dosing" valve?

The presence of black exhaust smoke is indicative of an engine running rich, often due to an excess of fuel in the combustion process. When a dosing valve, such as those found in diesel exhaust fluid (DEF) systems, leaks, it can allow too much diesel fuel or combustion byproducts to enter the exhaust stream. This results in incomplete combustion, leading to an increase in soot and unburnt fuel particles, which manifests as black smoke.

While other smoke colors can point to different issues—such as blue smoke indicating oil burning or white smoke suggesting coolant in the combustion chamber—black smoke specifically correlates with poor combustion efficiency usually stemming from an over-supply of fuel. Therefore, recognizing black smoke as a symptom of a leaking dosing valve is crucial for diagnosing issues related to exhaust emissions and fuel management within diesel engines.