In an EFI system, what does Closed Loop operation rely on?

In an Electronic Fuel Injection (EFI) system, Closed Loop operation primarily relies on feedback from the oxygen (O2) sensor located in the exhaust system. This sensor measures the amount of oxygen present in the exhaust gases, providing critical information about the air-fuel mixture being burned in the engine.

During Closed Loop operation, the engine control unit (ECU) uses this data to adjust the fuel injection in real-time. If the O2 sensor indicates that the engine is running too rich (too much fuel) or too lean (not enough fuel), the ECU will modify the fuel delivery to achieve the optimal air-fuel ratio, typically around 14.7:1 for gasoline engines. This dynamic adjustment helps ensure more efficient combustion, better fuel economy, and reduced emissions.

In contrast, the other options do not accurately describe the function of Closed Loop operation in an EFI system. Triggers limp home mode is related to safety and fault detection in the system, while a standard calibration or comparison to a carburetor does not capture the essence of how Closed Loop systems function effectively through continual adjustments based on actual exhaust readings.