How can line pressure be checked in an automatic transmission?

Using a pressure gauge is the correct method for checking line pressure in an automatic transmission because it provides a direct and accurate measurement of the fluid pressure within the transmission system. The gauge is specifically designed to connect to the transmission at designated test ports, allowing the technician to assess the pressure during transmission operation. This is crucial because line pressure can affect various functions, such as shifting performance, engagement of locks, and overall transmission operation.

In contrast, other methods such as visual inspection do not provide quantitative information about line pressure. While visual inspection can help identify leaks or other external issues, it cannot measure internal hydraulic pressures, which is essential for diagnosing transmission problems. Additionally, electronic diagnostic tools primarily read fault codes and do not directly measure hydraulic pressures unless they are integrated with specific hardware or sensors designed for that purpose. Therefore, relying on a pressure gauge is the most effective and accurate technique for checking line pressure in an automatic transmission.