Oxygen sensor effect on fuel trim

• A. It measures oil temperature to adjust fuel economy.
• B. It regulates airflow via the MAF sensor.
• C. The O2 sensor provides feedback on exhaust oxygen content; the PCM adjusts fuel trim to correct rich/lean conditions.
• D. It directly controls the ignition timing.

Answer: (C)

The oxygen sensor’s job is to tell the engine computer how much oxygen is left in the exhaust, and the PCM uses that feedback to continually adjust the fuel trim so the engine runs near the target air–fuel ratio. When the sensor detects lean conditions (more O2 in the exhaust), the PCM adds fuel; when it detects rich conditions (less O2), it trims fuel back. This adjustment happens in two stages: short-term fuel trim, which makes quick, small tweaks, and long-term fuel trim, which slowly adapts to persistent conditions to keep the mixture around the ideal ratio for efficient combustion and catalytic converter operation. This function is separate from oil temperature sensing, MAF-based airflow regulation, or ignition timing control, all of which serve different roles.