NOx Sensors

A dew point must be reached for effective operation and therefore also the monitoring of the NO_x sensor. This ensures that there is no longer any water in the exhaust system that could damage the NO_x sensors.

A reversible fault is set if the following monitoring functions detect a fault at the NO_x sensor. If the fault is determined in two successive driving cycles, an irreversible fault is stored and the MIL is activated.

• Detection signal or correction factor incorrect
• Line break or short-circuit between measuring probe and control unit of NO_x sensor
• Measured value outside the defined range for a certain period of time
• Operating temperature is not reached after a defined heating time
• The distance from the measured value to zero is too great in overrun mode (no nitrogen oxides expected)
• During the transition from load to overrun mode, the signal of the NO_x sensor does not drop fast enough from 80% to 50% (only NO_x sensor before SCR catalytic converter)
• If, despite a peak in the signal of the NO_x sensor before the SCR catalytic converter, at least a defined change in the signal of the NO_x sensor after the SCR catalytic converter is not determined this is interpreted as implausible.