Final answer:
A constant mid-range O₂ sensor voltage likely indicates that the 2. sensor is faulty, as a properly functioning sensor should display fluctuating voltages in response to changing oxygen levels.
Step-by-step explanation:
If the O₂ sensor voltage stays in the mid-range constantly at 2, it may indicate several possible scenarios. It could mean that the sensor is functioning properly, as a functional O₂ sensor can maintain a mid-range voltage under certain conditions. However, if the voltage never changes, even under varying conditions that should cause fluctuations in the sensor reading, it might also suggest that the O₂ sensor is faulty or contaminated, as a healthy sensor should display changing voltages in response to changes in oxygen levels.
Oxygen levels are critical for the accurate functioning of an O₂ sensor. In automotive applications, the O₂ sensor should fluctuate between low and high voltages corresponding to lean and rich combustion states. A constant mid-range voltage is abnormal and suggests a problem. If the sensor were unconnected, it would not give a voltage at all, so we can eliminate that option.
In summary, option 2, indicating that the O₂ sensor is faulty, is the most likely scenario provided the conditions for reading voltage were appropriate for revealing sensor fluctuations. Technicians would typically expect to see varying voltages if the sensor and the vehicle's engine were functioning correctly.