System Overview

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 diesel exhaust after treatment system is designed to reduce the levels of hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx), and particulate matter remaining in the vehicle's exhaust gases. Reducing these pollutants to acceptable levels is achieved through a 4 stage process:

A close coupled diesel oxidation catalyst (DOC) stage
A selective catalyst reduction (SCR) stage
A diesel oxidation catalyst (DOC) stage
A diesel particulate filter (DPF) stage

In stage 1, the close coupled DOC removes exhaust HC and CO through an oxidation process. After stage 1, reductant, also known as diesel exhaust fluid (DEF) or urea, is injected into the exhaust gases prior to entering the SCR stage. Within the SCR, NOx is converted to nitrogen (N2), carbon dioxide (CO2), and water vapor (H20) through a catalytic reduction fueled by the injected reductant. The exhaust then enters a second DOC. In the final or stage 4 process, particulate matter consisting of extremely small particles of carbon remaining after combustion are removed from the exhaust gas by the large surface area of the DPF