CDL Pre-Trip Inspection: The Complete Walkaround Guide

The pre-trip inspection is where most CDL applicants fail the skills test. Not because they don't know the material — but because they forget to say things out loud or skip components under pressure. This guide covers every step, every component, and every number you need. Practice with our free CDL pre-trip inspection practice tests.

The 7-Step Pre-Trip Inspection Method

Step 1: Engine Compartment (Engine Off)

Check these items with the engine off and the key in your pocket:

• Oil level: Check dipstick — adequate oil within safe range
• Coolant level: Check reservoir — adequate coolant (do not open if hot)
• Power steering fluid: Check level in reservoir
• Engine compartment leaks: Check for oil, coolant, fuel, or power steering fluid leaks
• Hoses: Check for fraying, cracks, leaks, or loose connections
• Wiring: Check for bare or damaged wires, loose connections
• Air compressor: Securely mounted, no oil/coolant leaks, no unusual noise
• Belt(s): Check for cracks, fraying, or excessive wear; check tension

Step 2: Cab Check / Engine Start

Get in the cab and check the following:

• Parking brake: Apply and confirm it holds
• Neutral/start: Start engine in neutral; listen for unusual noises
• Gauges: Oil pressure rises within seconds, ammeter/voltmeter shows charge, temperature normal
• Air pressure gauge: Build to 90 PSI within 45 seconds (single) or 60 seconds (combination)
• Governor cut-out: Needle stops between 125–135 PSI
• Mirrors: Clean, properly adjusted, securely mounted
• Steering wheel: Check for excessive play (no more than 10 degrees / 2 inches free play)
• Wipers and washers: Must function properly
• Defroster: Must function properly
• Horn: Must work (both air horn and electric horn if equipped)
• Heater: Must function
• Lights: Check all dash indicators, headlights (high/low), markers, turn signals, brake lights, hazard lights, and clearance lights

Step 3: Front of Vehicle

• Windshield: No cracks larger than a quarter in the driver's line of sight
• Windshield wipers: Blades intact, not worn, spring tension adequate
• Headlights: Both high and low beam functional, lenses clean and not cracked
• Turn signals: Both left and right front signals functional, lenses intact
• Clearance lights: All front clearance and identification lights functional
• Bumper: Securely mounted, no damage
• Grille: Securely mounted, no obstructions

Step 4: Sides of Vehicle

• Tires: Steering axle minimum 4/32 inch tread; all other tires 2/32 inch. No bumps, bulges, cuts, or ply separation. Adequate pressure (not visibly underinflated).
• Rims: No cracks, no bent or broken rims. No welding repairs on rims.
• Hub/axle seals: No oil leaks. Seals intact.
• Lug nuts: All present, tight, not missing. No rust trails (indicates loose nuts).
• Suspension: Springs — no broken, missing, or shifted leaves. U-bolts — tight, not missing. Shock absorbers — no leaks, securely mounted.
• Brake chambers: Securely mounted, no cracks, no air leaks.
• Slack adjusters: Less than 1 inch free play (manual adjuster). Not frozen or seized.
• Brake drums: No cracks. Not excessively worn.
• Brake hoses/lines: No cuts, cracks, or leaks. Properly secured, not dragging.
• Mud flaps/splash guards: Present, securely mounted, not dragging.
• Doors: Open, close, and latch properly. Hinges secure.
• Reflectors: All present, clean, not cracked.
• Side marker lights: All functional, lenses intact.

Step 5: Rear of Vehicle

• Taillights: Functional, lenses intact, clean
• Brake lights: Functional, activate when brake is pressed
• Turn signals: Both left and right rear signals functional
• Hazard lights: Functional
• Clearance lights: All rear clearance lights functional
• Reflectors: All present, clean, red in color
• Rear bumper/underride guard: Securely mounted
• Licensing plate: Present, visible, current

Step 6: Brakes / Air System Test

If your vehicle has air brakes, you must perform the air brake system test. See our complete air brakes guide for the full procedure and PSI numbers:

• Build-up time: 90 PSI in 45 seconds (single) or 60 seconds (combination)
• Governor cut-out: 125–135 PSI
• Low air warning: Activates at 55–60 PSI
• Spring brake engagement: 20–45 PSI
• Air leak rate: ≤4 PSI/min (single), ≤6 PSI/min (combination)
• Parking brake test: Vehicle does not move at low RPM

Step 7: Lights and Reflectors Final Check

Walk around the entire vehicle and verify all lights and reflectors are present, clean, and functional. This is a catch-all step to make sure nothing was missed.

What Automatically Fails the Pre-Trip Inspection

• Missing a safety-critical component: Forgetting to check brakes, steering, or tires
• Not knowing how to check a component: If the examiner asks you how you would check something and you can't explain it
• Excessive prompting: If the examiner has to prompt you more than a few times to continue
• Identifying a safety defect as acceptable: Saying a tire with visible cord is fine — it's not
• Missing the air brake test entirely if your vehicle has air brakes
• Steering axle tire tread below 4/32 inch
• Any visible fluid leak under the vehicle

Combination Vehicle Additions (Class A)

If you're testing in a combination vehicle, you must also inspect:

• Fifth wheel: Mounting bolts (all present, tight), jaws locked around kingpin, release arm in locked position, plate greased, no cracks or broken welds
• Kingpin: Not bent, cracked, or excessively worn
• Air lines (glad hands): Connected, no leaks, gaskets present and in good condition. Red = emergency, blue = service
• Electrical cord: Connected securely
• Landing gear: Fully raised, crank handle stowed, no damage
• Sliding fifth wheel: If equipped, locking pins engaged, release arm locked
• Converter dolly (doubles/triples): Pintle hook closed and latched, lunette eye secure, dolly axle and tires in good condition

Practice Tips: How to Ace the Pre-Trip

1. Practice out loud. The examiner can't read your mind. Say what you're checking, what you're looking for, and what would make it fail. Example: "I'm checking the left front tire. Tread depth is more than 4/32 inch. No bumps, bulges, cuts, or ply separation. Pressure is adequate."
2. Use a physical checklist during practice. Walk around a real vehicle and check every item. Take photos of components you don't recognize and look them up.
3. Develop a routine. Always start at the same point and go in the same direction. This prevents skipping components.
4. Touch every component. Physically touch or point to each item as you inspect it. This keeps you focused and shows the examiner you're actually checking.
5. Memorize the "leaks, cracks, mounts, missing, loose" pattern. For every component, check: Is it leaking? Is it cracked? Is it securely mounted? Is anything missing? Is anything loose?
6. Take free practice tests at CDL Study Buddy to reinforce the component names and what to look for.

Frequently Asked Questions