Circuit/System Description

For an overview of the component/system, refer to: Exhaust Aftertreatment System Description

The diesel exhaust aftertreatment system consists of an under hood catalyst and an underbody catalyst. The under hood catalyst consists of the main Diesel Oxidation Catalyst and the coated Diesel Particulate Filter (DPF). The Underbody catalyst contains the secondary selective catalytic reduction (SCR). One of the main purposes of the DPF is to collect particulates from the engine exhaust in order to minimize discharge of soot to the atmosphere. The 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. Three smart 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. he first NOx sensor is located at the turbocharger outlet and monitors the engine out NOx. The second NOx sensor is located in the exhaust pipe downstream of the SCR. and monitors NOx levels exiting the close coupled SCR. The third NOx sensor is located in the exhaust pipe downstream of the rear SCR and monitors NOx levels exiting the aftertreatment system. The smart NOx sensors communicate with the ECM over the serial data line.