What would be a reason for a vehicle to be marked deficient during a mechanical inspection?

A vehicle marked deficient during a mechanical inspection typically indicates that there are critical issues affecting safety or compliance with regulations. A cracked driver's side mirror falls into this category because it can obstruct the driver's view, making it unsafe to operate the vehicle. Proper visibility is essential for safe driving, and a damaged mirror poses a risk of accidents, thereby warranting a deficiency mark during an inspection.

Other factors like a clean windshield, new tires, or functioning lights do not indicate deficiencies and are generally seen as signs of proper vehicle maintenance. While those elements contribute to the overall safety and performance of the vehicle, they do not signify any deficiencies that would necessitate a report during a mechanical inspection.