Diesel Exhaust Fluid (DEF) Quality

Prior to the NOx sensor and the monitoring function becoming operational, the sensor must have reached its 'dew point'. This is the point where the moisture content in the exhaust gas has evaporated and can no longer damage the NOx sensor. In normal ambient conditions, this process typically takes around 6 to 10 minutes. If a malfunction is detected during the operation of the NOx sensor, a reversible fault is stored. If a malfunction is detected over two (NAS variants) or three (EU6 variants) consecutive drive cycles, a permanent fault is stored and the MIL is activated

The following monitoring is performed on the NOx sensors

• Signal plausibility and correction factor limits
• Circuit continuity between the sensor control unit and probe element
• Operating temperature reached after a defined heating period