What is an Oxygen Sensor? Structure and principle of operation

Oxygen sensors are  important in the operating system of cars, taking on the role of controlling the amount of fuel, contributing to improving engine efficiency and fuel economy. However, not everyone understands the structure, principle of operation as well as how to test oxygen sensors when they fail. Let’s take a brief  look at this type of sensor with RX Tradex.

1. What is an oxygen sensor?

An oxygen sensor in a car is an electronic device that measures the concentration of residual oxygen in exhaust gases, thereby supporting the engine to adjust the amount of fuel injected accordingly. This not only helps to optimize the performance of the vehicle, but also ensures compliance with emission standard regulations. When a problem occurs, the warning light system on the vehicle will turn on to warn.

Each different brand and model will use different types of sensors, including common types such as intake gas sensors, oxygen sensors, camshaft sensors,…

1.1. Structure of oxygen sensors in cars

The current oxygen sensor structure mainly uses the ZIRCONA type and is classified into two types: heated and unheated.

Heated Oxygen Sensor: equipped with an internal resistor that heats up the sensor quickly, allowing the sensor to reach a working temperature of 315 – 343 degrees Celsius (600 – 650 degrees Fahrenheit) in a short time.

The Unheated Oxygen Sensor does not have a self-heating mechanism, so it takes more time to reach the required working temperature on its own. This leads to the car taking more time to achieve the ideal carburetion ratio, because the fuel carburetor ratio is initially low.

1.2. Principle of operation of oxygen sensor

When the exhaust gas from the engine will pass through the pipe where the oxygen sensor is installed, it will come into contact with the probe of the sensor. Here, the sensor generates a voltage current inversely proportional to the amount of oxygen present in the exhaust gas and sends a signal to the ECU.

If the amount of oxygen in the exhaust gas is high, the voltage will be at 0.1V. Conversely, when the oxygen output is low, the voltage increases up to 0.9V. Obtaining the current figures, the ECU will automatically adjust the fuel injection time to achieve the ideal gasoline ratio, which improves the engine’s performance.

2. What does an oxygen sensor do

The main function of an oxygen sensor is to measure the excess oxygen content in the exhaust gas and send this data to the car’s ECU (central control unit). Based on this information, the system will evaluate the oxygen concentration and adjust the amount of fuel injected into the engine to match the amount of air intake.

In addition, the ECU also helps extend the fuel supply time to minimize the concentration of pollutants in exhaust gases such as COx and SOx,…

If the vehicle is not equipped with an oxygen sensor or the sensor fails, this will directly affect the performance of the engine, causing problems such as difficulty accelerating, more fuel consumption, or emissions exceeding engine standards.

3. Signs and causes of oxygen sensor failure

3.1. Causes of faulty oxygen sensors

The cause of oxygen sensor failure mainly comes from the quality of the input fuel. If the user uses poor-quality fuel, the toxic emissions produced will harm the parts involved in the chemical reaction with oxygen, resulting in damage to the oxygen sensor.

In addition, the sensor can also be damaged due to other causes such as broken wires, broken or crooked sensors,…

3.2. Signs of oxygen sensor failure

Signs that the oxygen sensor is damaged include:

The car consumes more gas

When the oxygen sensor fails, the data sent to the PCM loses accuracy or is completely absent, leaving the ECU to only estimate the amount of fuel based on the intake gas flow sensor. This causes excessive fuel pumping, even though the amount of oxygen in the exhaust gas is low, leading to excess fuel. If not fixed early, gasoline consumption will increase.

The car smoke smelled of live gasoline.

If you notice that the car smoke smells like live gasoline, it could be a sign of a faulty oxygen sensor. Because the amount of gasoline entering the combustion chamber is too much and is not completely burned, this excess gasoline will escape through the exhaust system.

The Check Engine light turns on continuously.

The Check Engine light is designed to warn when the engine or related parts are malfunctioning. If this light is on continuously, then the motor should be checked immediately to determine the cause.

4. How to test the oxygen sensor in a car

You need to prepare a voltmeter (Volt) to check the oxygen sensor.

Check the sensor while still installed on the motor

• The first step is to adjust the voltmeter to measure DC current below 1V. If the voltmeter has two negative (-) and positive (+) terminals, attach the positive (+) terminal directly to the sensor output.
• If the engine is hot, turn on the ignition but do not start the vehicle (the key is in the ON position), the voltage should range from 0.4 – 0.45 V.
• When the engine is hot, turn on the ON lock and change the speed by releasing the accelerator, the voltage needs to reach 0.5V.
• With the motor cold and the key in the ON position, the voltage should be between 0.1 – 0.2 V.
• When the motor is operating normally at temperatures between 600 – 650 degrees Fahrenheit (315 – 343 degrees Celsius), the voltage should be between 0.1 – 0.9 V.

Note: When performing the test, use adequate protective equipment and avoid touching the sensor directly by hand.

Check the sensor when disassembled from the motor

Start by securing the sensor on a flat surface with a clamping table or pliers, then attach the voltmeter conductors to the locations to be measured. Use a soldering iron to heat the tip of the sensor.

When the sensor is hot enough, the voltage on the voltmeter needs to reach 0.6V and remain for 20 seconds. Then, when the heating stops, the voltage drops by 0.1V/s. If the voltage difference is too large, it may affect the working performance of the sensor or kill the sensor.

After the inspection is completed, if no damage is detected, the car owner can clean the oxygen sensor to maintain its life and operating efficiency.

5. Conclusion

The car’s oxygen sensor helps the engine adjust the fuel injection level accurately. However, during operation, it is inevitable to encounter problems from parts, especially the sensor system.  Therefore, regular inspections and adherence to periodic maintenance milestones are necessary to detect problems early, prevent damage, and extend the life of the vehicle. In addition, if you want to grasp the latest advanced technologies and market trends, participate in NEPCON 2024 – The leading exhibition in Vietnam on SMT, test technology, equipment, and electronics manufacturing supporting industry organized by RX Tradex Vietnam. Register for exhibitors or visitors.