Can a bad oxygen sensor cause a vehicle to run rich?

A malfunctioning oxygen sensor can indeed cause a vehicle to run rich. The oxygen sensor plays a critical role in the vehicle's fuel management system by monitoring the amount of oxygen present in the exhaust gases. This information is used by the Engine Control Unit (ECU) to adjust the fuel-to-air mixture for optimal combustion.

When the oxygen sensor fails or provides inaccurate readings, it may incorrectly signal the ECU that there is not enough oxygen in the exhaust. In response, the ECU may increase the amount of fuel injected into the engine to compensate, resulting in a rich fuel mixture. This rich condition can lead to increased emissions, reduced fuel economy, and potential long-term damage to the engine or exhaust components.

Understanding the function of the oxygen sensor helps clarify why its failure can lead to an issue like running rich, emphasizing the importance of this component in maintaining efficient engine performance and compliance with emissions standards.