What do oxygen sensors do?

Many cars with Electronic Fuel Injection (EFI) systems are now equipped with oxygen sensors to maintain exhaust gas emission levels to remain environmentally friendly. Although the development of the EFI system is not new, the use of oxygen sensors in vehicles still has an important meaning, both for the environment and engine performance.

Now on this opportunity, we will share information regarding what do oxygen sensors do on the EFI system. The following is the oxygen sensor function and what they do for the engine.

1. Measure oxygen concentration in the exhaust gas.

The first oxygen sensor function is to measure the concentration of oxygen in the exhaust gas. Yes, the oxygen sensor detects the oxygen volume in the exhaust gases resulting from engine combustion.

Generally, oxygen sensors use an electronic component called Zirconia electrolyte (ZrO2). This component will react to the oxygen content and heat that flows along with the residual exhaust gases in the exhaust manifold.

Therefore, we will find the oxygen sensor only on the exhaust path of combustion, starting from the exhaust manifold (header) to the end of the car exhaust. But generally, the oxygen sensor is installed near the exhaust header or between the catalytic converters.

Oxygen sensors are usually connected directly to the ECM (Engine Control Module) using several wires (depending on the type and model used).

That way, the voltage sent by the ECM to the Oxygen Sensor can be directly received back by the ECM after the Zirconia electrolyte (ZrO2) reacts to the flowing exhaust gases. The reaction will result in the different values of voltage that have flowed from the previous voltage that ECM has given before.

Suppose the voltage received by the ECM from the oxygen sensor is at a voltage value of 0.1 volts. In that case, this indicates that the total oxygen concentration in the exhaust gas is in the range of 3%. It means that the air and fuel mixture in the engine is too thin (too much air compared to fuel).

And suppose the voltage received by the ECM from the oxygen sensor is 0.9 volts. In that case, it indicates that the amount of oxygen concentration in the exhaust gas is in the range of 0.3%. It means the mixture of air and fuel in the engine is too rich (too much fuel than air).

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2. As an input data for ECM to correct engine air-fuel ratio

The second Oxygen sensor function is as an ECM input data to correct the amount of air-fuel ratio mixture of the engine. The data is used to get an ideal ratio of air-fuel mixture conditions according to engine speed and load conditions.

Yes, to get an ideal combustion result and a powerful engine performance but still environmentally friendly, the ECM will use the input data in the form of a voltage from this oxygen sensor to correct the air-fuel ratio in the engine.

The ECM will adjust the length of time fuel injection into the combustion chamber and ignition timing to obtain the ideal air-fuel ratio according to engine speed and load.

For example, when there is a rich air-fuel ratio mixture, the ECM will speed up the fuel injection time to get less fuel mixed with air. The same applies to the opposite condition.

A change in the oxygen volume in the exhaust gas will immediately be re-measured by the oxygen sensor after the air-fuel ratio correction occurs.

When the value of the oxygen volume is correct by the data and engine requirements, the air-fuel ratio correction will temporarily stop. It will return to correction if the value of the oxygen content changes again.

So, the ECM will determine whether the air-fuel ratio is rich or lean and controls the injection timing based on the oxygen sensor's output voltage.

If the oxygen sensor malfunctions so that the output voltage becomes abnormal, the ECM will no longer control the air-fuel ratio accurately.