CDL Air Brake Cut-In Pressure
Last updated: September 2026
What is the air brake cut-in pressure?
The governor cut-in pressure is about 100 PSI. This is the pressure at which the air compressor starts pumping again after the system has been used.
Source: California Commercial Driver Handbook (DL-650)
What “cut-in” means
“Cut-in” is the point where the governor turns the compressor back on to refill the tanks. On the CDL test, the standard answer is about 100 PSI.
Cut-in vs cut-out
Cut-in (about 100 PSI) is when the compressor starts. Cut-out (about 125 PSI) is when it stops. Together they keep the system in its normal operating range of roughly 100–125 PSI.
A common mix-up
The “85 to 100 PSI within 45 seconds” figure is a buildup-rate test, not the cut-in pressure. Don't confuse the two.
Related Resources
Frequently Asked Questions
What PSI does the air brake governor cut in?+
About 100 PSI. The compressor starts pumping again once pressure drops to this level.
Is 85 PSI the cut-in pressure?+
No. 85 PSI relates to the air-pressure buildup test (85 to 100 PSI within 45 seconds), not the governor cut-in pressure.
This page is an independent study resource. It is not affiliated with the California DMV. Verify current requirements against official sources.