What does an O2 sensor measure in an engine's exhaust system?

The O2 sensor, or oxygen sensor, is a critical component in an engine's exhaust system, specifically designed to measure the concentration of oxygen in the exhaust gases. This measurement is vital for the engine control unit (ECU) as it helps determine whether the engine is running rich (too much fuel) or lean (too little fuel).

Based on the sensor's readings, the ECU can adjust the air-fuel mixture to optimize combustion efficiency, reduce emissions, and improve fuel economy. By maintaining the appropriate oxygen levels, the sensor plays a significant role in meeting environmental regulations and ensuring the engine operates at peak performance.

When the sensor detects high levels of oxygen in the exhaust, it indicates that there is excess air and too little fuel in the mixture, prompting the ECU to inject more fuel. Conversely, if it senses low levels of oxygen, it indicates a rich mixture, and the ECU will reduce fuel supply. Understanding this function is essential for diagnosing fuel mixture issues and overall engine performance.