California CDL Low Air Warning PSI
Last updated: September 2026
Is the CDL low air warning 55 or 60 PSI?
The low air warning must activate at or before 55 PSI. California's legal range is 55–75 PSI (California Vehicle Code §26506), and the federal rule (49 CFR §393.51) also uses 55 PSI. “60 PSI” is a common simplification in study guides — not the regulation.
Source: California Vehicle Code §26506 · California Commercial Driver Handbook (DL-650)
The short answer: 55 PSI
The DL-650 handbook requires the low air warning (buzzer, light, or wig-wag) to activate before the air pressure drops below 55 PSI. If it doesn't, the vehicle is not safe to drive.
California's legal range: 55–75 PSI
California Vehicle Code §26506 requires the warning device to activate at a fixed pressure of no more than 75 PSI and no less than 55 PSI (with the engine running). So the warning can activate anywhere in that range — and on large buses, it often activates higher (around 80–85 PSI).
Why some guides say 60 PSI
Many generic CDL study guides simplify the answer to 60 PSI. That number isn't the regulation — it's a rough midpoint of the 55–75 PSI range, and it can also be confused with when spring brakes begin to apply. For the California test, remember 55 PSI is the floor.
How it's tested
During the air brake check, you “fan” the brakes (rapidly press and release) to release air. The low air warning must come on before the pressure drops below 55 PSI. If it doesn't, the vehicle fails the air brake portion of the test.
Related Resources
Frequently Asked Questions
Is the low air warning 55 or 60 PSI?+
55 PSI is the floor. California's legal range is 55–75 PSI, and the federal rule also references 55 PSI. '60 PSI' is a common simplification in study guides.
What happens if the low air warning comes on while driving?+
Stop safely and park as soon as possible. The vehicle should be repaired before continuing.
How is the low air warning tested?+
By fanning the brakes with the key on and engine off (or on). The warning must activate before pressure drops below 55 PSI.
This page is an independent study resource. It is not affiliated with the California DMV. Verify current requirements against official sources.