If a technician finds that the pressure gauge reads 0 psi with the shutoff valve open, what is the next troubleshooting step?

The next troubleshooting step of checking the filter pressure drop is appropriate because a pressure gauge reading of 0 psi with the shutoff valve open indicates that there is likely a blockage or restriction in the system that is preventing airflow. A filter can become clogged over time with debris, dust, or other contaminants, which can lead to a significant pressure drop. By assessing the filter pressure drop, a technician can determine whether the filter is indeed the cause of reduced airflow and, thus, the zero pressure reading.

By contrast, inspecting wiring connections, replacing the regulator, or calibrating the pressure gauge do not directly address the immediate issue of a lack of pressure in the system. These actions would be more relevant in different scenarios, such as electrical faults or issues with component calibration, but the situation at hand suggests that airflow is being obstructed. Therefore, checking the filter pressure drop is the most logical and effective next step.