Circuit/System Description

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.

The selective catalytic reduction (SCR) system reduces oxides of nitrogen (NOx) emissions by injecting a metered amount of diesel exhaust fluid or reductant into the exhaust gas stream entering the SCR. Within the selective catalytic reduction catalyst, the reductant reacts with the NOx to form nitrogen, carbon dioxide, and water vapor. Upstream and downstream NOx sensors provide the engine control module (ECM) with engine-out and tailpipe-out NOx levels. The ECM uses two (NOx) sensors to control exhaust NOx levels. The first NOx sensor is located upstream of the reductant fluid injector and monitors the engine out NOx. The second NOx sensor is located at the outlet of the SCR and monitors NOx levels exiting the SCR The engine control module (ECM) varies the amount of diesel exhaust fluid (Reductant) or reductant added in response to changes in engine exhaust out NOx levels.