247SimpleTests
CDL · General

At what air pressure does the low air pressure warning signal typically activate?

Correct answer

Below 60 psi (usually around 60 psi or below)

  1. A Below 60 psi (usually around 60 psi or below)
  2. B At 125 psi
  3. C At 200 psi
  4. D It never activates

Why this is the answer

The LOW AIR PRESSURE WARNING signal must activate before pressure drops below 60 psi (typically activating at around 60 psi or below) — alerting the driver that air pressure is getting dangerously low. CDL air brakes. The warning may be a light, buzzer, and/or a 'wig-wag' device. If pressure keeps dropping, the SPRING (emergency/parking) BRAKES will apply automatically (around 20-45 psi). The driver must STOP SAFELY as soon as the low-pressure warning comes on — never continue driving with low air. Knowing the warning activates at/below 60 psi is commonly tested.
Source: FMCSA CDL Manual — Air Brakes, Low Pressure Warning

Practice more questions

This question is from our CDL Practice Tests practice test. Take the full practice test to test your knowledge across all General and other topics.

Take the Air Brakes practice test →

New to this exam? Our CDL exam guide explains the format, scoring, and how to prepare.

Related questions

General

Why should you drain the air tanks (reservoirs) regularly?

 General

If the low air pressure warning comes on while driving, what should the driver do?

 General

At approximately what air pressure do the spring (emergency/parking) brakes typically apply automatically if air pressure is lost?

 General

Why is it dangerous to 'fan' the brakes (rapidly pump them) repeatedly when descending a long grade with air brakes?

State-specific guides

Need information for your state? Our state guides cover local requirements, fees, and what to expect on exam day.

California Texas Florida New York Pennsylvania Illinois Ohio Georgia

Recommended study materials

Study guide

CDL Study Guide 2025–2026 (Trivium)

Complete prep for all CDL written tests: general knowledge, air brakes, combination vehicles, hazmat, and all endorsements. Includes full-length practice tests.

Check Price → Study guide

CDL Practice Tests & Flashcards (Accepted Inc.)

600+ practice questions covering every FMCSA knowledge area, plus 400 flashcards for endorsement prep.

Check Price → Study guide

Master the CDL Truck Driver's License (Arco)

Arco's classic CDL prep with in-depth FMCSA manual coverage, endorsement chapters, and scored practice exams.

Check Price →

As an Amazon Associate, CJ Affiliate, and AWIN publisher we earn from qualifying purchases. Links above are affiliate links. Full disclosure →