How does an oxygen sensor influence fuel metering in an EFI engine?

• A. It provides feedback to the ECU to adjust injector pulse width to maintain the target air-fuel ratio in closed-loop operation.
• B. It heats the exhaust to improve combustion.
• C. It measures oil temperature to regulate fuel viscosity.
• D. It controls the fuel pump speed.

Answer: (A)

The oxygen sensor’s job is to feed the engine computer with real-time information about how much oxygen remains in the exhaust, which tells the ECU whether the mixture is lean or rich compared with the target air-fuel ratio. In closed-loop operation, the ECU compares this sensor signal to the desired ratio (around 14.7:1 for gasoline) and makes small changes to the injector pulse width to adjust fueling accordingly. If the sensor shows a lean condition, the ECU lengthens the injector pulse to add more fuel; if it shows a rich condition, it shortens the pulse to reduce fuel. This continuous feedback keeps the engine running at the target AFR and reduces emissions. The sensor’s role isn’t to heat the exhaust, measure oil temperature, or directly control the fuel pump.