A car loses automatic transmission fluid but shows no leaks on the garage floor. What is the likely cause?

The likely cause of a car losing automatic transmission fluid without any visible leaks on the garage floor is often traced back to an internal leak, and the vacuum modulator is a common component that can cause this issue. The vacuum modulator is responsible for regulating the transmission's fluid pressure based on engine load, and if it has an internal leak, it can allow transmission fluid to escape into the intake manifold or engine, leading to a depletion of fluid levels without any visible signs on the ground.

This situation can result in poor shifting performance and may eventually cause significant damage to the transmission if not addressed. Understanding the internal workings of the transmission system, particularly how the vacuum modulator interacts with fluid levels, emphasizes the importance of diagnosing issues early to prevent further complications.