The section applicants fail most often. Pressure figures differ by state manual.
Most Air Brakes questions are the same federal material in every state. One question in the app is written for Nebraska alone, from the Nebraska Commercial Driver's Manual (Nebraska Specifics).
Failing to perform the air brake check or hydraulic brake check properly is scored as an automatic failure of the entire vehicle inspection test. All four parts must be explained and demonstrated.
One example, answer shown. Practicing the rest happens in the app.
The governor 'cut-out' pressure is about 125 psi. When tank pressure falls to roughly 100 psi, the governor cuts back in and the compressor resumes pumping.