Oxygen Sensor (O2)

The Oxygen Sensor (also known as lambda sensor) is an automotive component that started being implemented in vehicles in 1980. It is part of the emission control system components. If you are interested in finding out how it works and its importance for the vehicle, below we tell you everything you need to know about the O2 sensor. We will also help you identify its physical characteristics and possible failures.

What is the Oxygen Sensor?


It is an electronic sensing component. As we mentioned above, it is known as a lambda sensor. It is a rigid element since its shape is that of a small and short cylinder made of an element called zirconium and coated in ceramic so that it can withstand the temperature.

Some oxygen sensors have a small metal casing as protection and this has several lines of perforations for the combustion gases to enter through them.

The function of the Oxygen Sensor

The O2 sensor performs the basic function of informing the ECU of the amount of oxygen in the gases expelled by the running engine. Its purpose is to achieve efficient fuel consumption and release the least amount of harmful gases into the environment.

How does the Oxygen Sensor (O2) work?

To understand how the O2 Sensor works, you must first understand how the combustion process occurs. In order to burn the fuel inside the engine, a spark must be generated, which originates in the spark plugs by voltage from the coil. Air flows into the chamber of each cylinder through the intake valve. If there is air, oxygen is present.

Already there the atmosphere for the controlled explosion is created, fuel injection, air-oxygen, and spark. When this mixture is activated, combustion is generated, which in turn creates the gases that are expelled through the exhaust valves. They pass into the exhaust manifold and are detected by the oxygen sensor on their way through the exhaust pipe.

The gases cause a chemical reaction when in contact with the O2 Sensor. This reaction generates a voltage that travels to the vehicle's ECU and indicates the quality of the fuel mixture. From there, it will maintain or correct parameters such as fuel injection and air intake.


Types of Oxygen sensors

Although in physical appearance they are all very similar, at least some differences can be found in oxygen sensors. Perhaps the most notable is the wiring or the connection pins.

Some O2 sensors have 2, 3, or even 4 pins, which in turn will be shown in the output branch diagram.

Classification of Oxygen sensors

The classification of such sensors is given by the process itself to initiate its function.

  • Unheated: Older, first-generation oxygen sensors have an expected duration of many minutes. This is due they have no heating or ignition voltage signal. Therefore, it must wait for the exhaust gases themselves to heat it up.
  • With heating: These have 3 or 4 wires and through one of them the sensor receives an electrical excitation that allows it to actuate within seconds of engine ignition.

Oxygen Sensor Failures

The most frequent failure is related mainly to the fuel mixture. For example, if there is little air or oxygen in the mixture, there will be an excess of unburned fuel at ignition. This condition is known as a rich mixture, and it is very harmful because there will be more polluting gases.

If it is the opposite, less fuel injection and more air, the mixture is defined as lean, affecting engine performance.

Other O2 sensor problems

There are other common failures due to the position where the Oxygen Sensor is located and associated with high temperature, for example:

  • Sulfated connection.
  • Overheated wiring.
  • Crystallized and brittle harness.

Interference of the Oxygen Sensor on other systems

The O2 sensor has a strong impact on the fuel injection system. In addition to how it regulates the air intake to the engine. Of course, it achieves this by transmitting the corresponding electrical signals to the ECU.

Depending on the amount of oxygen in the exhaust gases, the ECU will adjust the fuel injection timing. This process is continuous thanks to the Oxygen Sensor.

Symptoms of damaged Oxygen Sensor

The symptoms are defined, although they can also affect other sensors. If this sensor fails, you will notice the following symptoms:

  • Increased fuel consumption.
  • Increased exhaust gas emissions.
  • Problems with power, when starting.

How to measure or test the Oxygen Sensor

To check the operation of the O2 sensor of a cable, the method is quite basic, either referred to in bank 1, or bank 1 sensor 2 with a double sensor.

  • Using a DC multimeter, place the tip of the multimeter on the positive wire of the sensor, and with the other tip, make contact with the negative of the battery. The grounding phase is created by the sensor itself by its metal casing.
  • The Oxygen Sensor should flash many times in less than one second.
  • If you measure the voltage, it should be as close to 0.9 volts as possible, as a maximum value. The minimum should be close to 0.1.
  • If the sensor has 2 or 3 wires the procedure is similar, only with the other clamp of the multimeter you will ground another of the wires that is ground.
  • Finally, there is the one with 4 wires, this Oxygen Sensor has a signal wire and a constant ground wire, which comes from the ECU. So the values will be more defined.

OBD2 protocol codes concerning the O2 Sensor

When scanning the sensor you may see the following codes, which have the following meanings:

How to maintain and clean the Oxygen Sensor?

Cleaning the sensor is very easy and you can do it yourself. Have some thinner or carburetor cleaner handy.

  • Check that the engine and exhaust are cooled down. Carefully disconnect the harness.
  • Remove the sensor and apply solvent to it so that it drains and the dirt comes out.
  • Allow it to dry at room temperature and reinstall it.

It is important to maintain or replace the Oxygen Sensor at least every 40,000 to 50,000 kilometers.

Where is the Oxygen Sensor?

To know its location look at the exhaust pipe, specifically at the engine outlet, you will find it after the exhaust manifold. There are vehicles of modern automotive technology, to which the manufacturers have integrated two oxygen sensor units. They place one at the exhaust manifold outlet and the other where the catalytic converter goes. This allows them to measure the total efficiency of the emissions system. You can find out the exact location of the O2 sensor by acquiring the car's electrical diagrams.


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