What does a NOX sensor do?

How does a NOX sensor work?

The NOX sensor has two chambers. In the first chamber (which is similar to that of a broadband sensor) the oxygen content in the exhaust gases is measured at around 10 ppm. The current required for this is inversely proportional to the air/fuel ratio and can be used to correct the NOX signal depending on the measured air/fuel ratio. The NOX reaction, the separation into nitrogen and oxygen, takes place in the second chamber. The current required to keep the area around the platinum-rhodium electrode free of oxygen is proportional to the NOX concentration and therefore supplies the measurement signal.

Why is a NOX sensor used?

Since modern petrol engines have direct injection and the combustion is proportionally hotter than conventional engines, more NOX is produced than is permitted for type approval in Europe.

Therefore, manufacturers must install a NOX catalyst and NOX sensor that store, measure and convert these gases into less harmful gases.

What's wrong?

Since the NOX sensor has a limited lifespan, it will fail sooner or later. If the signal that the NOX sensor emits is no longer within a certain bandwidth, the engine control unit will store an error, causing the engine to go into limp mode, increasing fuel consumption and causing the engine to stall easily. The engine failure light also comes on. In many cases, the NOX sensor is defective.

Solution?

ChipTuningPower can ensure that the engine management no longer needs this sensor. We can switch this off completely for you so that the engine light no longer lights up and the car no longer runs in "emergency mode". They also get through the periodic motor vehicle inspection without any problems. This often saves hundreds of CHF, since a new sensor quickly costs at least 500 CHF.

Lambda probe

A lambda sensor is a sensor in the exhaust of a petrol car that measures the oxygen content in the exhaust gas and forwards it to the engine management system. The lambda value is an indicator of the effectiveness of the combustion. Depending on the lambda value, this is adjusted by the engine management system by adjusting the composition of the fuel and air ratio, by adjusting the fuel injection and by changing the injection timing of the injectors.

Vehicles after 2000 have a second oxygen sensor behind the catalytic converter to check its effectiveness.

The probe

The sensor element is a ceramic cylinder coated with porous platinum electrodes on the inside and outside. The whole is protected by a metal grille. It works by the difference in oxygen between the exhaust gas and the outside air, creating a voltage or changing its resistance depending on the type of sensor.

The sensors are only effective when heated to approximately 316°C. This is why most oxygen sensors have a heating element that quickly heats the ceramic tip. This enables faster control of the mixture composition. Older probes without heating elements are heated by the exhaust gases. Between the time the engine is started and the time the probe is at the correct temperature, there will be a few minutes without heating.

The probe usually has four wires, a signal wire, usually black, a ground wire (grey) and two for the heating element (white). Older non-electrically heated sensors had one wire (the signal line and ground through the outlet) or two wires (a signal line and a ground line).

Lambda signal

The signal from the probe for the catalyst varies from 0.1 to 0.9 volts at resp. with a poor or rich mixture. With the stoichiometric combustion of petrol, this is 0.45 V, the lambda value is then 1.