Which action is critical in maintaining control when brakes fail?

Shifting to a lower gear is essential for maintaining control when brakes fail. This technique, known as engine braking, utilizes the engine's resistance to slow down the vehicle. By downshifting, the vehicle’s speed can be reduced more effectively without relying on the brakes, which may be ineffective at that moment. This allows for better control over acceleration and deceleration, particularly on downhill slopes or when encountering emergency situations.

Utilizing this method also helps in steering control since you will have a more manageable speed which makes it easier to navigate turns or obstacles. It allows the driver to respond more smoothly to the driving conditions rather than abruptly.

Other options such as slamming on the brakes could lead to loss of control or skidding, while turning off the engine can eliminate power steering assistance, making it difficult to steer. Maintaining hands on the top of the wheel can be beneficial for steering control, but it does not directly address the critical need to slow the vehicle down when the brakes are failing.