Within what range must a vehicle’s oxygen sensor readings be during an emissions test?

The range of 0.1 to 0.9 volts for a vehicle’s oxygen sensor readings during an emissions test is the correct choice because this range corresponds to the operational parameters of typical oxygen sensors used in emissions systems. Oxygen sensors monitor the level of oxygen in a vehicle's exhaust, providing crucial information for the engine control unit to optimize air-fuel mixture for efficient combustion.

In this range, the sensor can effectively switch between rich and lean conditions, helping to maintain the ideal combustion process. Readings below 0.1 volts typically indicate a very lean mixture, while readings above 0.9 volts suggest a rich mixture. Maintaining these readings within the specified range is vital for compliance with emissions regulations and ensuring that vehicles operate efficiently while minimizing harmful emissions.