Select the best answer for the question. 7. The voltage value at which a Zirconia oxygen sensor switches from rich to lean or from lean to rich is A. 0.9 V (900 mV). B. 0.5 V (500 mV). C. 0.25 V (250 mV). D. 0.45 V (450 mV).
Select the best answer for the question. 7. The voltage value at which a Zirconia oxygen sensor switches from rich to lean or from lean to rich is A. 0.9 V (900 mV). B. 0.5 V (500 mV). C. 0.25 V (250 mV). D. 0.45 V (450 mV).
The Correct Answer and Explanation is:
Correct Answer: D. 0.45 V (450 mV)
Explanation:
A Zirconia oxygen sensor, commonly known as a narrowband O2 sensor, is a key component in automotive emission control systems. It measures the oxygen content in the exhaust gases to help the engine control module (ECM) maintain the optimal air-fuel ratio, known as the stoichiometric ratio, which for gasoline engines is approximately 14.7:1.
This type of sensor operates by generating a voltage signal based on the difference in oxygen levels between the exhaust gas and outside air. The sensor’s voltage output ranges from about 0.1 volts (lean condition) to about 0.9 volts (rich condition). The point at which the sensor transitions or “switches” between indicating a lean or rich mixture is known as the stoichiometric threshold, and that occurs at approximately 0.45 volts (450 millivolts).
At 0.45 V, the air-fuel mixture is very close to ideal (stoichiometric). The engine control system interprets voltages above 0.45 V as a rich mixture (too much fuel, not enough oxygen), and voltages below 0.45 V as a lean mixture (too much air, not enough fuel). Because of this, the ECM constantly adjusts the fuel injection to maintain this ideal balance, a process called closed-loop fuel control.
It’s important to note that Zirconia sensors are not linear. They act more like a switch than a gauge—they rapidly flip between high and low voltage rather than providing a gradual change. This makes them effective for detecting whether the mixture is rich or lean but not how rich or lean it is.
Therefore, the switching voltage point of 0.45 V is critical in engine control systems, and thus, option D is the correct answer.
