What happens to fuel efficiency when an O2 sensor is malfunctioning?

When an O2 sensor is malfunctioning, the fuel efficiency often decreases because this sensor plays a crucial role in regulating the air-fuel mixture that the engine uses for combustion. The O2 sensor monitors the level of oxygen in the exhaust gases and provides feedback to the engine control unit (ECU). This feedback enables the ECU to adjust the fuel injection and air intake accordingly to achieve the optimal combustion ratio.

With a faulty O2 sensor, the ECU may receive incorrect signals about the oxygen content in the exhaust. As a result, it may either inject too much fuel (enriching the mixture) or not enough fuel (leaning the mixture), both of which can lead to inefficient combustion. When the air-fuel mixture is not optimal, it can result in increased emissions, reduced power, and worse fuel efficiency, thus causing a decrease in overall fuel economy. Therefore, the malfunction of the O2 sensor has a direct and negative impact on fuel efficiency.