Selective Catalyst Reduction Components
EU6 vehicles have a single post Selective Catalyst Reduction (SCR) NOx sensor module and a post SCR NOx sensor located in the exhaust system after the SCR catalytic converter.
NAS vehicles have a pre SCR NOx sensor module and a pre SCR NOx sensor located in the exhaust system after the catalytic converter and Diesel Particulate Filter (DPF) assembly. A second post SCR NOx sensor and post SCR NOx sensor module is located in the exhaust system after the SCR catalytic converter.
NAS vehicles also have a post SCR soot sensor located in the exhaust system after the SCR catalytic converter.
Selective Catalyst Reduction NOx Sensor and Module
| ITEM | DESCRIPTION |
|---|---|
| 1 | Selective Catalyst Reduction (SCR) NOx sensor |
| 2 | SCR NOx sensor module |
The NOx sensor comprises an integrated heater and sensor control module. The sensor is used to measure the O2 and the NOx concentration in the exhaust gas of a diesel engine. The sensor and the control module are replaced as an assembly.
The NOx sensor is an evolution of the wide band Heated Oxygen sensor (HO2S). 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 NOx sensor control module sends data via a private Controller Area Network (CAN) bus. The data is received by the Powertrain Control Module (PCM) for monitoring the effectiveness of the Selective Catalyst Reduction (SCR) system.
The functionality of the SCR catalytic converter is monitored by the NOx sensor(s) and NOx modelling software in the PCM.
On EU6 vehicles the NOx mass entering the SCR catalytic converter is measured by a software model within the PCM.
On NAS vehicles the NOx mass entering the SCR catalytic converter is measured by a pre SCR catalytic converter NOx sensor.
On EU6 and NAS vehicles, the NOx mass emitted from the SCR catalytic converter is measured by a post SCR catalytic converter NOx sensor.
Values are measured over a certain period of time and the actual NOx reduction is compared to a minimum expected criteria calculated within the PCM.
If there is a failure of a NOx sensor or if the NOx emissions fail to reach a pre-determined threshold:
- The PCM will store a Diagnostic Trouble Code (DTC)
- Relevant messages will be displayed to the driver in the Instrument Cluster (IC) message center
- The Malfunction Indicator Lamp (MIL) in the IC will be illuminated.
It is a legislative requirement to prevent the engine from starting if a fault occurs in the SCR system. As long as the fault is still present the IC message center will provide a distance countdown to customer after which engine start will not be possible.