What does an O2 sensor do in a vehicle?

The O2 sensor, also known as an oxygen sensor, plays a critical role in monitoring the oxygen levels in a vehicle's exhaust gases. Its primary function is to provide feedback to the engine control unit (ECU) about the air-fuel mixture being burned in the engine. By measuring the amount of oxygen present in the exhaust, the O2 sensor helps the ECU adjust fuel injection and ignition timing for optimal engine performance and emissions control.

When the air-fuel mixture is too rich (meaning there's not enough oxygen), the O2 sensor detects this condition and indicates to the ECU to reduce the fuel supply. Conversely, if the mixture is too lean (too much oxygen), the ECU can add more fuel. This constant adjustment helps ensure complete combustion and improves efficiency while reducing harmful emissions that could contribute to pollution.

Understanding the role of the O2 sensor is fundamental to grasping how modern engines operate and maintain compliance with environmental regulations.