If your vehicle has a properly functioning dual air brake system and minimum-sized air tanks, the air pressure should build from 85 to 100 psi within ____ seconds.

Check the Rate of Air Pressure Buildup To perform this test, the engine must be running at normal operating idle, typically 600–900 rpms. Observe the air gauge to determine if the pressure builds at the proper rate. For dual air systems, the pressure should build from approximately 85 to 100 psi within 45 seconds. For single air systems (in pre-1975 vehicles), the pressure should build from approximately 50 to 90 psi within 3 minutes.
For testing purposes, you must verbalize the parameters of the test and identify if the vehicle met the appropriate standards.
[Commercial Driver Handbook]