How to Master the CDL Pre-Trip Inspection: In-Cab Portion

Every day a commercial driver begins with one critical task: the pre-trip inspection. This is a comprehensive check that ensures all vital components of your truck are in optimal working condition, setting you up for a safe and efficient day on the road. From inspecting tires and brakes to testing lights and fluid levels, this process is much more than a quick glance at your truck—it’s a detailed, legally required safety measure. Skipping or rushing through this inspection isn’t an option; it’s a key responsibility that can prevent accidents and keep you, as well as everyone else on the road, safe.

For this reason, we take this portion very seriously at New Sound CDL School. We make sure our students are prepared and well-versed for this part of commercial driving since it's an essential part of the job. As well as that, it's also one of the most difficult parts of the CDL exam due to its requirement of thorough truck knowledge, memorization, and the ability to explain various parts of the vehicle’s systems. In our courses, we break down each step with hands-on practice, equipping you to confidently pass this portion of the CDL exam and setting you up for a safe, reliable career. This guide will walk you through each detail of the in-cab inspection, from air brakes to gauges, so you’ll know exactly what to expect on test day and beyond. We've also recorded a detailed pre-trip inspection video if you're more of a visual learner.

Understanding the In-Cab Pre-Trip Inspection

The in-cab pre-trip inspection can be broken down into three main parts:

1. Air Supply System – This is the most crucial part of the inspection, and it’s a "make or break" segment. You need to pass this section to proceed with the rest of the test.
2. In-Cab Inspection – Similar to checking your car at home, this includes inspecting windows, mirrors, and safety equipment.
3. Parking Brake and Service Brake Tests – Here, you'll ensure the brakes are functioning correctly.

The examiner will sit in the sleeper area to observe as you perform each test. Let’s dive into the details.

Step 1: Safety Start and Air Supply System Check

The inspection starts with a safety start:

1. Depress the Clutch and make sure the gear shifter is in neutral.
2. Set the Parking Brakes and turn the key to the "on" position. Confirm that the ABS lights come on and turn off correctly. Start the truck.

Now, you’re ready to perform the air governor cut-off check:

• Pump the service brakes until the air pressure falls below 90 PSI.
• The air governor should cut out when pressure reaches between 120-140 PSI. It’s fine to rev the engine to 1,000 RPM to speed this up.
• When you hear the air governor cut out, check the pressure. For example, it may cut out at around 135 PSI, indicating a successful test.

Step 2: Air Leakage Rate Test

Next, you’ll perform the air leakage rate test:

1. Place the shifter in gear, turn off the truck, then turn the key back to the “on” position, and release the clutch.
2. Release both the tractor and trailer protection valves after ensuring the clutch is released.

For this test, press and hold the service brake to apply around 40 PSI. Monitor the gauges to ensure the combination vehicle doesn’t lose more than 4 PSI within 60 seconds. You may use a stopwatch to count the time. If you hold the pressure steady and the gauges indicate no more than a 4 PSI loss, you pass this part of the test.

Step 3: Low Air Warning Device Check

In this part, you’ll test the low air warning devices:

• Pump the brakes slowly to release air until the low air warning light or buzzer activates, ideally above 55 PSI. For instance, if the light comes on at 60 PSI, the test passes.
• Ensure the warning light stays on continuously.

Step 4: Emergency Brake Test

The emergency brake test verifies that both protection valves pop out between 20-45 PSI. To perform this:

• Pump the brakes until the protection valves pop out at around 25 PSI.
• Watch the valves closely rather than the gauges to confirm they both pop out simultaneously.

With the air supply system test complete, turn the key off. Congratulations on completing the most technical portion of the pre-trip inspection!

Step 5: In-Cab Inspection

Now it’s time for the in-cab inspection:

1. Perform another safety start: Depress the clutch, set the shifter to neutral, check that the parking brakes are set, and turn the key to "on."
2. Confirm the ABS lights are functioning properly before starting the engine.

While waiting for the air pressure to rise, complete the in-cab safety checks:

• Emergency Equipment: Ensure a fully charged fire extinguisher is secured, three red reflective triangles are in the back, and you have six spare fuses.
• Mirrors and Windshield: Check mirrors are clean and adjusted. Inspect the windshield for cracks or obstructions.
• Windshield Wipers and Washers: Verify that the wiper arms and blades are secure and functioning, and that washers operate smoothly.
• Heater and Defroster: Test the heater and defroster to ensure they’re working properly.
• Horns and Lighting Indicators: Test the city horn, air horn, and dashboard indicators for right and left turn signals, four-way flashers, and high beams.

After completing these checks, the air governor should cut out at 120-140 PSI, indicating you’re ready for the final brake checks.

Step 6: Brake Tests

The last part of the pre-trip inspection is to confirm that the parking brakes and service brakes are working:

1. Tractor Parking Brake Test: Release the trailer parking brake, place the shifter in gear, and gently try to move forward. Resistance should confirm that the tractor parking brake is working properly.
2. Trailer Parking Brake Test: Set the tractor brake, release the trailer brake, and attempt to move forward. Resistance indicates the trailer parking brake is functioning.
3. Service Brake Test: Release both parking brakes, shift into gear, and move forward at about 5 mph. Gently apply the service brake. A smooth stop without pulling left or right shows that the service brakes are working correctly.

Step 7: Light Check with Examiner

Finally, ask the examiner to step outside for an external light check. Follow these steps:

1. Turn on all necessary lights, including clearance lights, headlights, high beams, turn signals, and four-way flashers.
2. Have the examiner confirm the side marker lights and the brake lights at the rear of the truck.
3. After the light check, turn the key off, and meet the examiner at the front of the vehicle to proceed with the out-cab inspection.

Washington’s Premier CDL School

The pre-trip inspection can be a daunting task to take on, especially for the first time. But we know that practice makes perfect. With New Sound CDL School’s expert trainers, you’ll have the close support of industry professionals with decades of commercial driving experience who’ll teach and train you to proficiency. Our curriculum includes hands-on practice that will familiarize you with the equipment and inspection process until it becomes second nature. We’re committed to providing you everything you need to confidently perform this inspection on test day and every day after. Our instructors guide you patiently through each step, providing tips and personalized feedback to help you succeed.

Our school boasts a high first-time passing percentage of 80% and offers translations in Spanish, Russian, and Ukrainian for those who prefer it. Our commitment is to provide you with an instruction environment that gives you every tool and opportunity you need to succeed. Ours is a proven program with instructors and systems that you can not only trust, but actually enjoy.

If you’re ready to begin your journey toward a successful career in commercial driving, apply today or contact us to learn more about our programs and see how we can prepare you for the CDL exam and life on the road.