Watch the Air Brake Check Step by Step
The 3 Parts of the Air Brake Check
The air brake check is usually taught and performed in a specific order.
On the CDL Skills Test, this part matters because the examiner is looking for both the correct procedure and the correct pressure ranges. According to the FMCSA CDL manual, the three key parts are
- The applied pressure test
- The low-air warning test
- The spring brake pop-out test.
The manual also states that if you do not perform all three correctly, you can automatically fail the vehicle inspection portion of the test.
The Setup: Perform a “Safe Start”
Before you can test the brakes, you have to safely start the truck and build up the air in your tanks.
- Turn the key to the “ON” position: Do not start the engine yet. Just turn the key so the dashboard gauges and electronics turn on.
- Check your setup: Verify the transmission is in Neutral and both of your parking brakes are applied (pulled out).
- Start the engine: Turn the engine fully on.
Now, your goal is to build the air pressure up to 120 to 140 PSI. You can give the truck a little bit of gas to raise the RPMs (no higher than 1500) to make the air compressor work faster. Keep watching the gauges until you hear a loud “sneeze” from the air tanks. That sneeze indicates your air pressure is full!
Now that the setup is done, it is time for the 3 Steps of the Air Brake Test.
(CRITICAL WARNING: Once the tanks are full, turn the engine OFF, and turn the key back to the ON position. If you forget to turn the key back on, your dashboard electronics won’t work, and you will fail!)
Step 1: The Applied Pressure Test
First, push in the yellow brake valve (tractor) and then the red brake valve (trailer). This moves the air from the tanks into the lines.
- Press your foot firmly on the brake pedal and hold it there.
- Wait for exactly one minute.
The Goal: Watch your gauges. You must not lose more than 4 PSI during that one minute. This proves your system doesn’t have a massive air leak.
Step 2: The Low-Air Warning Test
Next, you need to make sure the truck will warn you if the air pressure is dropping.
- Begin pumping the foot brake.
- The low-air warning light and buzzer should come on before 55 PSI.”
The Goal: Watch the dashboard. Make sure the warning light and buzzer activate before the gauge hits 55 PSI.
Step 3: The Spring Brake Pop-Out Test
Finally, you need to prove that the emergency spring brakes will automatically pop out and stop the truck if you lose too much air.
- Continue pumping the foot brake even faster.
- Between 20 and 45 PSI, both parking brake valves should pop out.
The Goal: Keep pumping and watching the red and yellow valves. Between 20 and 45 PSI, both valves will loudly pop out. (Do not pull them out with your hands, they must pop out on their own!)
Need Help Passing the Air Brake Check?
If the air brake check still feels confusing, you are not alone.
At Driving Academy, our professional instructors help students learn difficult parts of the CDL Skills Test. Instead of trying to memorize everything on your own, you can train with instructors who walk you through the process!
Click the button below and learn how our instructors and Guaranteed CDL Program can help you get ready for the test.
Common Mistakes on the Air Brake Road Test
I’m going to be straight with you: this is going to be one of the most difficult parts of the road test itself. Why? Because the grading is incredibly strict. If you miss just one thing on the checklist, you completely fail the test and have to restart from the beginning again.
The biggest reason I see students fail is the lack of repetitions. During your training here at Driving Academy, we give you a step-by-step checklist to help you build that muscle memory. But remember, during the road test itself, you’re not allowed to use the checklist. You are completely on your own.
Because of the pressure, students often make small errors that cost them the entire test. In my experience, here are the two most common mistakes that will lead to an instant fail:
- Forgetting the Key: After you hear the sneeze, turn the engine off, but you must turn the key back to the “ON” position (no engine). A lot of people forget this step. If the key isn’t on, your dashboard warning lights and buzzer won’t work. And what do you think is going to happen? You’re going to fail.
- Touching the Valves: During the final pop-out test, you must let the truck do the work. It is very, very important that you keep pumping those brakes until both valves pop out on their own. If you reach over and touch them or pull them out yourself, you fail.
Why the Air Brake Check Matters?
The manual explains that the air brake check is meant to confirm that the safety devices operate correctly as pressure drops. It also warns that if the low-pressure warning does not work, you could lose air pressure without knowing it, which could cause emergency braking in a single-circuit system or increased stopping distance in a dual system. The manual also says excess air loss can lead to losing your brakes while driving.
When even one mistake can cost you the test, proper training can make a big difference. Contact Driving Academy and learn how our instructors can help you prepare for the air brake check and the rest of the CDL Skills Test.
FAQs About the Air Brake Road Test
The air brake road test usually refers to the air brake check performed during the pre-trip inspection portion of the CDL Skills Test. It is not the written air brake exam. Instead, it is the part where you show the examiner that you know how to check the air brake system correctly before driving.
Yes. The FMCSA manual states that if you fail to perform all three parts of the air brake check correctly, you automatically fail the vehicle inspection test portion of the CDL Skills Test.
Yes. For the applied pressure portion, the FMCSA manual says to shut off the engine before completing that part of the test. It also says to chock the wheels if necessary.
According to the FMCSA manual, air pressure should not drop more than 3 psi in one minute for a single vehicle or 4 psi in one minute for a combination vehicle during the applied pressure test.
The air brake check is important because it shows that the brake system can hold pressure, warn the driver when pressure gets too low, and activate the spring brakes when necessary.
Disclaimer: Exact wording and pressure ranges may vary slightly by state examiner or testing vehicle.
