EMISSIONS
SCR — ective Catalytic Reduction
Definition
SCR is the chemical process by which urea (AdBlue) reacts with NOx in the exhaust catalyst to form harmless nitrogen and water vapor. The SCR catalyst itself is a vanadium- or zeolite-coated honeycomb that operates between 200-400°C.
Why workshops care
SCR efficiency below threshold (P20EE) is the most common SCR DTC. Causes: cold ambient, plugged catalyst, faulty NOx sensors, or aged urea. Same patching workflow as AdBlue OFF.