What is a lambda sensor (O2 sensor)?

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You want to understand the tasks and function of the lambda sensor or O2 sensor? Then read our blog article to understand everything you need to know about this component.

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What is a lambda sensor?

Lambda sensor

In simple terms, a lambda sensor or O2 sensor is a sensor that is installed in the exhaust tract of the vehicle to measure the residual oxygen concentration in the exhaust gas. On the basis of this value, the sensor can also ensure optimum mixture preparation/mixture composition in order to reduce or maintain the emissions of the engine.

Depending on the vehicle, up to 4 lambda sensors can be installed. A distinction is made here between pre-catalyst and post-catalyst probes.

How does a lambda sensor work?

Once the probe reaches its operating temperature of approximately 350 degrees, the residual oxygen content in the lambda probe produces a voltage change. This means in the actual sense that the functional principle is based on an oxygen comparison measurement.

The probe compares the residual oxygen in the exhaust gas (which should be approx. 0.3 – 3 %) with the oxygen content in the ambient air (approx. 20.8 – 21 %).

  • If the residual oxygen content is less than about 3%, the mixture is said to be “rich” (too much fuel). Here the probe voltage rises to 0.9 V.
  • If, however, the residual oxygen content is 3%, this is referred to as a “lean mixture” (too much air). Here the probe voltage is 0.1 V.

As mentioned previously, the lambda sensor measures the residual oxygen content in the exhaust gas. After the measurement, an electrical voltage is sent to the engine control unit. Based on the voltage transmitted by the probe, the engine control unit can detect whether a “rich” or “lean” mixture composition is present.

Different types of lambda sensors

There are essentially two types of lambda sensors used in a production vehicle. The so-called jump probe and the broadband probe.

Broadband probe

The great advantage of the broadband probe is that it can measure much more accurately. This is because, compared to a normal “jump probe”, the broadband probe can measure accurately even in rich and lean mixtures. Often, the broadband probe is also referred to as a “linear” probe.
Nowadays, only wideband probes are installed in new vehicles, as this type of probe meets all the criteria required for modern exhaust gas after treatment.

Jump probe

In contrast to the broadband probe, the jump probe can only send a so-called jump signal to the engine control unit. This means that the jump probe can only distinguish between rich and lean mixtures, but cannot measure exactly like the broadband probe. For this reason, the jump probe is now rarely installed in new vehicles.

What happens if the O2 sensor is defective?

If the lambda sensor is defective, the engine control lamp is usually the first to light up and the engine control unit switches to an “emergency program”. This also means that the engine control unit drastically reduces the engine power. It is also usually the case that fuel consumption increases.
Of course, the exhaust gas values of the engine also deteriorate.

Symptoms of a defect

  • Illumination of the engine control lamp (MIL)
  • Jerking of the engine during acceleration
  • Increased fuel consumption
  • Power loss
  • Increased smoke from the exhaust pipe
  • Failure to pass the exhaust emission test

Diagnosis and repair of faults on the O2 sensor/lambda sensor

f you suspect any issue, we recommend running a diagnosis using an OBD2 adapter, first. This will read your error memory from your ECUs. In many cases you can find out when an error (DTC) has been detected and what specifically the error is.

OBD adapters and diagnostic equipment can be used to diagnose a variety of engine problems, regardless of make or model. The issues found vary between simple sensor defects and more complex problems, such as turbocharger defects. In some specific cases, an OBD adapter can help fixing an issue. Sometimes just clearing old trouble codes (DTCs) will help, saving you a trip to the repair shop.

Whether you like fixing stuff yourself or you are a professional, a diagnostic device is a valuable tool that every driver should have in his car.

How much does a lambda sensor cost?

The price varies depending on the model and the vehicle. As a rule, a O2 sensor costs between 100 and 300 dollar. However, it is important to note that some probes for certain types of vehicles can be significantly more expensive.

How can I check and change the lambda or O2 sensor?

If the lambda sensor is defective and the check engine light is on, in most cases there is no way around replacing the sensor.

For most vehicles, no special tools are required. Of course, there are also vehicles where the exchange is difficult and special tools are needed.

To give you an overview of how complex it is, you can find a general guide for the replacement of the lambda sensor here.

1. Find the lambda sensor

The lambda probe is normally located between the catalytic converter and the engine. It may be that the probe is relatively hidden on the exhaust. Therefore, you should look very carefully.

2. Disconnect the plug

Once you have found the component, you can disconnect the connector.
Attention. If you have just driven the vehicle, the exhaust is still very hot. There is a risk of burns!

3. Removing the old O2 sensor

Unscrew the old probe. If the probe is very difficult to turn, use rust remover to avoid damaging the thread.

4. Screwing in the new sensor

Check the thread in the exhaust before you install the new component. If there is any damage, it must be repaired beforehand.

5. Plug in connector

Once the sensor is screwed back in place and tight, you can reconnect the connector of the lambda sensor to the wiring harness of the engine. Make sure that there are no traces of oxidation in the engine connector.

6. Clear error memory

Once you are done with the work, clear the error memory of the engine control unit.

7. Perform test drive

Test drive the vehicle after clearing the engine control unit fault memory. Also during the test drive, check if the check engine light stays off. Once you have finished the test drive, read the fault memory again to check whether the fault has been re-entered or not.

Keep in mind, that every car has different software and modules built-in. Therefore specific features will vary with every model.


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