Lambda sensors / NOx sensors

The lambda sensor supports the catalyst in its work

The lambda sensor, also known as the exhaust probe or control probe, is a sensor that measures the oxygen content of the exhaust gases. Based on the values determined, the engine control system regulates the fuel-air mixture to achieve optimum combustion. The catalytic converter can thus significantly reduce the emission of harmful gases. Low-emission exhaust gases are particularly important in conurbations in order to prevent driving bans and reduce environmental pollution.

For this reason, the control probe is an important component of the exhaust system and it is worthwhile to rely on high quality and fitting accuracy. With the original lambda probes from the vehicle manufacturers, you can play it safe. How important the exhaust probe is, which other probes are added for the exhaust measurement, which lambda value means what and much more can be seen in the lower section of this page.

Where is the lambda sensor located and what do the different lambda values mean?
What happens when the lambda sensor fails?
How does a NOx sensor work and what happens if it goes faulty?
Buy lambda sensor or continue driving with defective component?

Where is the lambda sensor located and what do the different lambda values mean?

The control probe sits in front of the catalytic converter in the exhaust manifold. The diagnostic probe sits after the catalytic converter. Most engines only have one exhaust probe installed, but sports cars can even have one for each cylinder. The lambda sensor influences the performance, consumption and environmental impact of the engine. Its results are referred to as so-called lambda values. These values allow conclusions to be drawn about the mixture ratio of fuel and air. In the following you will find the lambda values with their corresponding meanings:

Lambda value less than 1: More fuel in the mixture than can be burned. One also speaks of a "rich mixture". Here more power can be called up and it comes to a higher consumption, as well as to a higher environmental impact.
Lambda value greater than 1: More air in the mixture than is necessary for combustion. There is thus an excess of air and is therefore also referred to as a "lean mixture". The fuel consumption is lower, but performance is reduced and problems can also arise with the catalytic converter.
Lambda value = 1: The mixture contains exactly as much air as is required for the combustion of the fuel. There is a balance between consumption and performance and is therefore environmentally friendly. The so-called lambda window provides the greatest cleaning performance in the catalytic converter.

What happens if the control probe fails?

Even standard probes can wear out, for example if they:

are exposed to excessive temperatures
experience chemical stress too high
too high mechanical loads such as vibrations of the vehicle act on them

If the lambda sensor is defective, the control unit no longer receives any useful data. The engine control goes into emergency mode and greases the mixture more strongly. This leads to increased fuel consumption and increased environmental pollution. The emission of smoke clouds can also point to a defective control probe.

The defective exhaust probe is usually detected and stored by the vehicle diagnostic system. In addition, there are also so-called diagnostic probes which are installed behind the catalytic converter. It checks whether the lambda sensor in front of the catalytic converter still functions correctly. If this is not the case, the driver will be informed accordingly.

How does a NOx sensor work and what happens if it goes faulty?

The NOx sensor sits behind the catalytic converter and is divided into two chambers one behind the other. In the first, the lambda value is measured and the oxygen is split into ions. In the second chamber, the remaining nitrogen oxide is split into oxygen and nitrogen. The current flowing in this process indicates the concentration of nitrogen oxide in the exhaust gases. This value is transmitted to the control unit. If there are deviations, the engine control lamp lights up.

NOx sensors also wear out over time. This can lead to incorrect values being sent to the control unit, triggering incorrect actions. In the worst case, this causes the engine to switch to emergency mode and run only at reduced power. In this case at the latest, a workshop should be visited as soon as possible.

Buy lambda sensor or continue driving with defective component?

From a technical point of view, a defective lambda sensor does not affect the engine performance. However, it is not advisable to continue with a defective control probe. On the one hand, an intact probe is TÜV-relevant. On the other hand, the additional costs due to increased fuel consumption are significantly higher than the fast and cost-effective replacement of the exhaust probe.

Before buying lambda sensors, please consider the installation location. Should it be the control probe before the catalytic converter or the diagnostic probe after the catalytic converter? In addition, there are heated and unheated variants. As a rule, unheated lambda sensors are used in older vehicles, whereas newer vehicle models rely on the heated solution. Other criteria include the type of connector and the length of the cable. For the exact distinction of the components, select the appropriate vehicle in the vehicle search above, so the search is reduced to the correct vehicle model.

In order to guarantee a long service life, it is worthwhile to focus on quality. You get the best quality with the original parts of the vehicle manufacturer. Simply select your vehicle and you will receive the suitable control probe for your vehicle. If you have any further questions, please feel free to contact our service team.