Selective Catalyst Reduction NOX Sensor

The Selective Catalyst Reduction (SCR) NOx sensor is located in the exhaust pipe downstream of the SCR catalytic converter. On North American Specification (NAS) market vehicles there is an additional NOx sensor fitted upstream of the SCR catalytic converter. The NOx sensor comprises a sensor element attached to a dedicated control module with a hardwired connection.

The sensor and the control module are replaced as an assembly. The NOx sensor is an evolution of the wide band oxygen sensor. The sensor element is constructed from special ceramics and contains two oxygen density detecting chambers that work together to determine the NOx concentration in the exhaust gas. The control module sends a message via the private Controller Area Network (CAN) bus to the Powertrain Control Module (PCM) for monitoring the effectiveness of the SCR system.