What does the O2 sensor in an Electronic Fuel Injection System report?

The O2 sensor in an Electronic Fuel Injection (EFI) System plays a critical role in monitoring the combustion efficiency of an engine. Its primary function is to measure the amount of oxygen present in the exhaust gases. By analyzing this data, the O2 sensor provides valuable feedback to the engine control unit (ECU) regarding the air/fuel ratio being used during combustion.

When the O2 sensor detects a deviation from the target air/fuel ratio, it sends a signal to the ECU, which then adjusts the fuel injection accordingly to maintain optimal combustion conditions. This feedback loop ensures that the engine runs efficiently, reduces emissions, and improves overall performance. In contrast, the other options do not accurately describe the primary role or behavior of the O2 sensor in the context of an EFI system. For instance, the sensor does not report the content of fuel in the exhaust, nor is its operation dependent on conditions like exhaust temperature or an open-loop system. Its function revolves around continuously monitoring and reporting the air/fuel mixture's effectiveness through the oxygen content in the exhaust.