A bad modulator would most likely cause which of the following?

A faulty modulator plays a crucial role in how an automatic transmission operates, particularly in managing shift points. The modulator is responsible for controlling the pressure in the transmission that affects when and how the gear shifts occur. If the modulator is not functioning properly, it may lead to shifts that are too late and can feel harsh.

When the modulator signals are incorrect due to a fault, the transmission may not receive the appropriate pressure required for smooth shifting. This can result in delayed shifts, where the vehicle continues to operate in the current gear longer than intended before finally shifting. Additionally, a harsh shift occurs when the engagement into the next gear is forceful rather than smooth, often causing a jolt or feeling of hard engagement as the transmission attempts to synchronize the gears without the right pressure modulation.

Understanding this function emphasizes the importance of the modulator in enhancing driving comfort and transmission longevity. Therefore, this connection between a faulty modulator leading to late and harsh shifts clarifies why this is the most accurate answer choice.