When does 'lock down' occur in an automatic vehicle?

'Lock down' in an automatic vehicle typically occurs when the vehicle is experiencing a condition that restricts its movement, but it's important to clarify that the term most commonly refers to the engagement of the transmission to prevent the vehicle from accelerating unintentionally. This is often a safety feature in automatic transmissions to help with vehicle control.

In this context, when selecting a lower gear for better control, it allows the engine’s braking effect to slow the vehicle down, particularly in situations like descending steep grades. This helps maintain control and prevents the vehicle from picking up excessive speed. By engaging a lower gear, the transmission effectively “locks” the gear, giving the driver more control over the vehicle's speed and responsiveness.

Other options may refer to situations that do not inherently trigger a 'lock down' condition. For example, parking the vehicle does not induce any active engine-braking control; pressing the accelerator too hard is generally associated with unwanted acceleration, and coasting downhill without proper gear selection does not engage the braking mechanisms of the vehicle. Hence, selecting a lower gear comes out as the most appropriate action relating to 'lock down' in the context of managing vehicle speed more effectively.