An O2 (oxygen) sensor measures the amount of unburned oxygen in your car's exhaust gases and sends this real-time data to the engine computer (ECU or PCM).
How It WorksAir-Fuel Ratio: The computer uses this data to adjust the balance of air and fuel entering the engine, aiming for the ideal stoichiometric ratio of 14.7 parts air to 1 part fuel.• Rich vs. Lean:• A rich mixture means there is too much fuel and not enough oxygen, which wastes gas and clogs emissions systems.
• A lean mixture means there is too much oxygen and not enough fuel, which can cause dangerously high combustion temperatures and damage internal engine parts.
• Upstream and Downstream:
• Upstream sensors (before the catalytic converter) monitor the initial exhaust and help fine-tune fuel delivery.