CDL General Knowledge TestAir Brakes (if applicable)Hard
A driver is operating a vehicle with a dual air brake system. The air pressure gauge for the primary system indicates 65 psi, while the secondary system indicates 120 psi. What action should the driver take immediately?
- AApply the parking brake and stop the vehicle safely.
- BEngage the emergency brake to bypass the primary system.
- CIncrease engine RPM to build pressure in the primary system.
- DContinue driving, but monitor the secondary system closely.
Show answer & explanationAnswer & explanation
Correct answer: A. Apply the parking brake and stop the vehicle safely.
In a dual air brake system, if one system's pressure drops below 60 psi (or significantly low), it indicates a major problem. The vehicle should be stopped safely and immediately to prevent brake failure.
Why the other options are wrong
- B. The emergency brake (parking brake) uses spring brakes and is not designed for continuous braking or to bypass a failing service brake system during operation.
- C. While increasing RPM might temporarily help build pressure, it won't fix the underlying leak or malfunction causing the pressure drop, and the vehicle is still unsafe.
- D. Driving with one system significantly compromised is unsafe and risks complete brake failure.
Dual Air Brake System Failure
A condition where one of the two independent air brake systems (primary or secondary) in a commercial vehicle loses significant air pressure.
- Each system operates half of the service brakes.
- Loss in one system still allows partial braking.
- Requires immediate and safe stop due to reduced braking capacity.
Memory trick: Dual System Down? STOP Now, Don't Clown Around!