Oxygen Sensor Function

Possible Defects & Costs

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There is often confusion about the topic of oxygen sensors in vehicles. Many people don’t even know that there are at least two oxygen sensors in a car, both of which play a crucial role in its operation. If an oxygen sensor is faulty, you won’t pass the vehicle inspection, as the emission values will be distorted. How oxygen sensors work in vehicles, their purpose, and how you can prevent a defect are all explained in this article. We’ve also prepared a guide for replacing the diagnostic sensor for you.

Contents
  1. 1) What is the Oxygen Sensor and where is it installed?
  2. 2) Preventing Issues with the Oxygen Sensor
  3. 3) Lambda sensor costs
  4. More Articles

1) What is the Oxygen Sensor and where is it installed?

Nowadays, a modern vehicle has at least two oxygen sensors. These are located on the exhaust system and regulate or monitor the emission values. However, both sensors are similar and can sometimes be used interchangeably. In practice, it is not uncommon for the same sensor to be used as both a control sensor and a diagnostic sensor. This mainly depends on the car model and the manufacturer of the oxygen sensor.

The Control Sensor:

The oxygen sensor BEFORE the catalytic converter is the control sensor. The control sensor measures the oxygen content in the exhaust gas of a combustion engine and sends the measured signal to the engine control unit. This unit then adjusts the air-fuel mixture of the engine to regulate the oxygen content in the exhaust gas. This ensures that the engine operates optimally and reduces emissions. Control sensors are essential for optimizing the vehicle's exhaust gas purification and reducing emissions, and they are installed in almost all modern motor vehicles.

Lambda sensor/control sensor (before catalytic converter)
Oxygen sensor upstream of the catalytic converter (control sensor)

The Diagnostic Sensor:

The oxygen sensor AFTER the catalytic converter is the diagnostic sensor and usually has a longer cable than the control sensor. The diagnostic sensor is primarily used to identify and diagnose issues in the engine or exhaust cleaning system. For instance, it detects faults in the catalytic converter or diesel particulate filter and sends an error code to the engine control unit. The diagnostic sensor checks whether the control sensor is functioning correctly and can also compensate for deviations. Additionally, the diagnostic sensor is used to read the emission values for the vehicle inspection or emissions sticker.

Lambda sensor/diagnostic sensor (after catalytic converter)
Oxygen sensor after the catalytic converter (diagnostic sensor)

2) Preventing Issues with the Oxygen Sensor

There are several steps you can take to prevent a defect in an oxygen sensor:

Keep the engine clean: A clean engine reduces deposits in the oxygen sensor, which can lead to faults.
Use high quality fuel: Always use the better fuel for your vehicle. If you use poor quality fuel, this can lead to deposits in the lambda sensor.
Check the air filter regularly: A clogged air filter can impair the performance of the engine and lead to deposits in the oxygen sensor.
Check the exhaust system: Make sure that the exhaust system is in good condition and that there are no leaks. Leaks in the exhaust system can lead to falsified values or to error messages in the engine control unit.

Don’t forget that the oxygen sensor is a wear part and will inevitably need to be replaced sooner or later. However, early detection of issues and regular maintenance can help extend the lifespan of the oxygen sensor.

3) Lambda sensor costs

The cost of an oxygen sensor can vary depending on the manufacturer, model, and year of the vehicle. Additionally, you need to differentiate between a control sensor and a diagnostic sensor.

The price for a diagnostic sensor can range between 20 and 170 euros.
The price for a control sensor can range between 50 and 250 euros.

In some cases, it may be necessary to replace the oxygen sensor along with other parts, such as the exhaust manifold or exhaust pipe. In such cases, the repair can become more expensive.
Additionally, you should ensure that you use a high-quality and original replacement oxygen sensor. Original oxygen sensors have a longer lifespan and function reliably.

*Favorable offers for Oxygen Sensors can be found here:

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We have prepared a guide for replacing the diagnostic sensor for you. The replacement is simple and can be done at home without much effort.


* Affiliate links are marked with a *. Nothing changes for you and the offer/price remains the same. You can find more information about affiliate links here.

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