Detail explanation of NOx sensor working process

2019-6-7 22:05:47

Detail explanation of NOx sensor working process 

The main function of the N0x sensor is to detect whether the N0x concentration value in the exhaust gas is out of limits, and to diagnose whether the catalytic converter muffler is aging or removed.The N0x sensor communicates with the control unit via the CAN bus, which has its own diagnostic function. After the sensor self-test has no fault, the control unit instructs the heater to heat the N0x sensor. If the sensor signal is not received within the heating process if the maximum heating time limit is exceeded, it is determined that the sensor heating is not reliable.

1. "No power status"

A. In this state, 24V power is not supplied to the sensor.

B. In the case where the body igniter switch is off, this is the normal state of the sensor.

C. The sensor does not have any output at this time.

2. "There is power supply - sensor inactive state"

A. At this time, the power has been supplied to the sensor through the ignition switch.

B. The sensor enters the preheating phase, and the purpose of the preheating is to evaporate all the moisture on the sensor head.

C, the preheating phase will last for about 60 seconds.

3. When the ignition switch is turned on, the N0x sensor will heat up to 100 C.

4. Wait for the ECM to issue a "dew point" temperature signal ."Dew point" temperature means that there will be no moisture present in the exhaust system that can damage the N0x sensor. The current dew point temperature is set to 120 C, and the temperature value is the value measured with reference to the EGP outlet temperature sensor.

5. When the sensor receives the dew point temperature signal from the ECM, the sensor will self-heat to a certain temperature (maximum 800 C) - Note: If the sensor head is exposed to water, the sensor will be damaged.

6. After heating to the working temperature, the sensor starts normal measurement work.

7. The NOx sensor sends the measured NOx value to the ECM via the CAN bus, and the engine ECM monitors the NOx emissions  with this information from time to time.