What must be done before checking the cab height control valve operation?

To ensure accurate operation of the cab height control valve, it is essential to disconnect the linkage before performing any checks. This disconnection allows for a proper assessment of the valve's functionality without interference from the suspension system's operational components. By isolating the valve, one can accurately determine if it is functioning correctly and responding as intended when checking for height adjustments.

Disabling the linkage prevents any potential movement or influence from the connected systems, which could lead to misleading results during the testing process. This step is critical to identifying whether the issue lies within the valve itself or is caused by other components in the suspension system.

While checking for leaks, maintaining low air pressure, and inspecting for defects are all useful troubleshooting steps, they are not prerequisites for checking the cab height control valve's operation. Ensuring the linkage is disconnected first sets the stage for an effective and precise evaluation of the valve in question.