CDL Air Brake Leak Rate
Last updated: September 2026
What is the CDL air brake leak rate?
Static (foot off brake): single 2, combination 3 PSI/min. Applied (foot on brake): single 3, combination 4 PSI/min. California also lists triple combination at 5 static / 6 applied.
Source: California Commercial Driver Handbook (DL-650)
Static leak test
With the engine off, parking brakes released, and foot off the brake pedal:
| Single vehicle | 2 PSI/min |
| Combination vehicle | 3 PSI/min |
| Triple combination (California) | 5 PSI/min |
Applied leak test
With the engine off and foot holding the brake pedal:
| Single vehicle | 3 PSI/min |
| Combination vehicle | 4 PSI/min |
| Triple combination (California) | 6 PSI/min |
Triple-combination leak rates are California DL-650 content — most other states only test single and combination vehicles.
Static vs applied — what's the difference?
Static measures leaks with the brakes released. Applied measures leaks with the brakes held. Applied allows 1 PSI/min more because the brake chambers and lines are pressurized.
How the test is performed
Charge the system to full pressure, turn the engine off, release the parking brake, and let the gauge settle. Time one minute and watch the pressure drop. If the loss exceeds the limit, the vehicle has a leak that must be fixed.
Related Resources
Frequently Asked Questions
What is the static leak rate for a combination vehicle?+
3 PSI per minute. A single vehicle allows 2 PSI/min static.
What is the applied leak rate for a single vehicle?+
3 PSI per minute. A combination vehicle allows 4 PSI/min applied.
What's the difference between static and applied?+
Static is measured with the brakes released; applied is measured with the brakes held. Applied allows 1 PSI/min more.
This page is an independent study resource. It is not affiliated with the California DMV. Verify current requirements against official sources.