The oxides of Nitrogen are responsible for damaging the respiratory system, creating acid rain, and polluting the air. These have a significant adverse impact on our health and environment. But unfortunately, these are massively produced from diesel and petrol engines we use in the form of cars and engine-generators. Thus, controlling such emissions is of utmost importance, and that’s where NOx sensors come into play. In this article, we will discuss what a NOx sensor is and how it works. Let’s start with the basics.

What is a NOx Sensor?

A NOx (Nitrogen Oxide) sensor monitors nitrogen oxide levels emitted by a diesel or petrol engine and generator. It is a device that measures the concentration of nitrogen oxides and gives signals to the NOx reduction system. It has been an essential part of diesel engines for decades; however, modern petrol vehicles also have it to keep an eye on harmful emissions. It gives real-time measurements of NOx and oxygen concentration and helps the NOx reduction system to act accordingly. With that said, it plays a vital role in controlling NOx emissions from vehicles. It is the only way to comply with the regulations and keep our environment and lives safe.

NOx and Their Adverse Effects

Nitrogen Oxides or NOx include Nitrogen Dioxide (NO2), Nitric Oxide (NO), Nitrogen Monoxide (N2O), Nitrogen Pentoxide (NO5), and other oxides of Nitrogen. These oxides are highly reactive, and when they are emitted from vehicles, generators, and engines, they harm our health and the environment. Higher concentrations of NO2 in the air result in various human respiratory diseases. Long exposure causes asthma and other respiratory infections, especially in children and the elderly. All these nitrogen oxides are highly reactive, and they react with other chemicals and compounds to create ground-level ozone pollution; this ozone formation at the ground is nothing more than a curse. Moreover, they are responsible for solid particles and liquid droplets in the air, which are extremely small to see through the naked eye and harmful to health. Other than the adverse health effects, these oxides also disturb the environment. They contribute to the creation of acid rain, which harms lakes and forests. The particles in the air pollute the air and make it hazy, which causes difficulty to see. Thus, controlling NOx emissions is essential, and NOx sensors play a vital role in that. Without this sensor, we won’t have any idea of how much harmful gases are being emitted from our vehicles, which will result in higher concentrations of nitrogen oxides in the air.

How Does a NOx Sensor Work?

The NOx sensor is located at the exhaust of a vehicle to sense the levels of nitrogen oxides emitted from the engine. It contains electrochemical cells that generate an electrical signal after a reaction occurs with nitrogen oxides. There are usually two or three electrochemical cells. The primary one is made up of a Nernst cell, and its cell potentials can be determined by the Nernst equation. It helps in regulating the air/fuel ratio to reduce the emission of nitrogen oxides.  The second cell converts nitrogen oxides into Oxygen and Nitrogen, converting harmful gases into harmless products. It is made up of ceramic and has a layer of rhodium. The catalyst present inside the NOx sensor generates a voltage when it reacts with the nitrogen oxides. The voltage serves as an electrical signal and high voltages reflect higher concentrations of nitrogen oxides emission. The signal goes to the Engine Control Unit (ECU), which commands Selective Catalytic Reduction (CSR) to reduce the emission of nitrogen oxides.NOx sensor works along with the other elements of the system to sense the emission of nitrogen oxides and reduce them to a safe level according to the regulations.

Maintaining and Troubleshooting NOx Sensors

A NOx sensor ensures the emission of nitrogen oxides from an engine within safe limits. Therefore, we can’t bear any fault or issue with the sensor. And that’s why users should know about maintenance and troubleshooting.


NOx sensors have a limited lifespan, and it is usually specified by manufacturers in hours. For instance, a NOx sensor can have a lifespan of 3,600 hours. After his period, the sensor will not function properly and create various issues. This is the time you need to replace it with a new one. Once the sensor completes its lifespan, it starts creating various issues, such as increased fuel consumption, error or warning lights, etc.NOx sensors can stop working or fail before their lifespan due to multiple reasons, such as

  • Mechanical Damage: NOx sensors are fragile, and their components can break in case of a strong impact.
  • Temperature fluctuations: When you drive in snowy and cold areas, NOx sensors face abrupt changes in the temperature.
  • Presence of Water/Moisture: Water can corrode NOx sensors and prevent them from working. Make sure your NOx sensor has high water resistance.
  • Dirt Formation: The buildup of dirt is a common cause of inaccurate readings and shorter lifespans of NOx sensors.
  • Excessive Oil Use: If the consumption of engine oil is excessive, it could damage the sensors

Within the lifespan of a NOx sensor, you have to maintain it. The common issue is the buildup of soot, which prevents the sensor from taking correct measurements and also deteriorates its life.


If you encounter an error from P2200 to P225 on the onboard diagnostic system, it would probably be due to the NOx sensor. The engine warning light also indicates a failure of electronic components, which could be anything, including NOx sensors. If the vehicle does not start or show limp status, it could be due to any fault or failure of the NOx sensor. When you face such issues, get the sensor cleaned and see if it works. Although NOx sensors are automatically cleaned, you can try manual cleaning. The next options are repair or replacement.

Want a Reliable NOx Sensor?

If there is any issue with the NOx sensor, the best way is to get it replaced as soon as possible. It not only disturbs the performance of vehicles but also pollutes the environment. Getting the NOx sensor cleaned or repaired works, but once in a blue moon. Replacing it is an easier and better option. Get a reliable NOx sensor that is compatible with your vehicle and offers certain features, such as

  • Real-time monitoring
  • NOx and O2 concentration
  • Water resistance or waterproofing
  • Toxicity resistance
  • Long lifespan

Check out our NOx sensors for Volvo, DAF, Man, Mercedes-Benz, Scania, and Cummins.


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