P20EE – SCR NOx Catalyst Efficiency Below Threshold Bank 1

P20EE Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P20EE Possible Causes

Exhaust Leaks,Fuel contamination,Faulty Diesel Particulate Filter (DPF),Faulty NOx Sensor,Diesel Exhaust Fluid,Faulty Selective Catalyst Reduction (SCR) Catalyst

P20EE Description

The selective catalytic reduction 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 Diesel Particulate Filter (DPF). Within the selective catalytic reduction catalyst, the reductant reactswith 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 the 2 NOx sensors to control exhaust NOx levels. The NOx sensor measures the amount of NOx and oxygen in the exhaust system. The first NOx sensor is located at the outlet of the turbocharger and monitors the engine out NOx. The second NOx sensor is located in the DPF that monitors NOx levels exiting the DPF. The ECM varies the amount of reductant added by varying the reductant injector duty cycle in response to changes in engine exhaust out NOx levels.