Pre-Trip Inspection Guide: Step-by-Step CDL Walkthrough

Pre-Trip Inspection Overview

A pre-trip inspection is a systematic check of your vehicle's safety-critical components before operating it. Federal Motor Carrier Safety Regulations (49 CFR 396.13) require every CMV driver to be satisfied the vehicle is in safe operating condition before driving it.

For CDL testing purposes, you will demonstrate the pre-trip to an examiner while verbally explaining what you are checking and why. In daily practice, you perform the same checks but without the narration. The goal is the same: identify any defect that could make the vehicle unsafe to operate.

The inspection follows a logical flow: start with the engine compartment (hood up), move to the cab interior, check all exterior lights, then do a complete walk-around covering every component from front to rear. For Class A CDL drivers, this includes the coupling system and full trailer inspection.

Engine Compartment

Start with the engine compartment. Make sure the parking brake is set and the wheels are chocked before raising the hood.

• Engine oil level: Check the dipstick. Oil should be between the minimum and maximum marks. Look for signs of contamination (milky appearance indicates coolant mixing with oil).
• Coolant level: Check the coolant reservoir or radiator overflow tank. The level should be within the indicated range. Never open the radiator cap on a hot engine. Look for leaks around hoses and connections.
• Power steering fluid: Check the reservoir level. Low fluid indicates a leak somewhere in the steering system.
• Windshield washer fluid: Verify the reservoir is adequately filled.
• Belts and hoses: Inspect all belts for cracks, fraying, or excessive wear. Hoses should be firm without cracks, bulges, or leaks. Check clamp connections.
• Wiring: Look for frayed, cracked, or hanging wires. Check battery connections for corrosion and tightness. Batteries should be secured and not leaking.
• Air compressor: Check the compressor for oil leaks and secure mounting. Inspect the air lines connected to it.
• Water pump: Look for leaks around the pump housing and weep hole.
• Leaks: Check for any fluid puddles or wet spots under the engine. Look for oil, coolant, power steering fluid, or fuel leaks.
• Steering components: If visible, check the steering gear box for leaks and secure mounting. Inspect the pitman arm, drag link, and steering linkage for looseness or damage.

Cab and Controls

Enter the cab and check all controls, gauges, and safety equipment:

• Parking brake: Ensure it is engaged and holds the vehicle. The parking brake button/valve should be in the applied position.
• Clutch and gearshift: Press the clutch and check for smooth engagement. Shift into neutral and verify the gearshift moves freely.
• Steering wheel: Check for excessive play (more than 10 degrees of free movement before the wheels respond is too much). The steering column should be firmly mounted.
• Gauges: Start the engine and check all gauges: oil pressure (should build within seconds), water temperature, voltmeter/ammeter, air pressure gauge (should build to operating range), and fuel gauge.
• Air pressure build-up: Monitor the air pressure gauge. The system should build from 85 to 100 psi within 45 seconds (with the engine at operating RPM). If it takes longer, there may be a compressor or air system problem.
• Low air pressure warning: When testing air brakes, the warning buzzer or light should activate below 60 psi.
• Windshield and wipers: Check for cracks, chips, or visibility obstructions. Test windshield wipers and washer spray on all speeds.
• Horn: Test the horn to verify it works.
• Heater and defroster: Verify both function, especially in cold weather.
• Safety equipment: Confirm the presence of three reflective triangles, a properly charged fire extinguisher (check gauge and inspection date), and spare fuses.
• Seatbelt: Check that the seatbelt retracts and latches properly.

Lights and Mirrors

All lights must be functioning and clean. This check requires turning on different light circuits from the cab and then walking around the vehicle:

• Headlights: Test both low and high beams. Both should illuminate properly without flickering.
• Turn signals: Activate left and right turn signals. Verify all front, side, and rear turn signal lights flash correctly.
• Hazard flashers (4-way): Activate and verify all flasher lights work on the tractor and trailer.
• Marker and clearance lights: Front, side, and rear clearance lights must all be functioning. These are amber on the front and sides, red on the rear.
• Brake lights: Have someone press the brake pedal (or use the trailer hand brake to activate trailer brake lights) while you walk around. All brake lights should illuminate brightly.
• Mirrors: Adjust all mirrors (flat, convex, and hood mirrors) for proper visibility. They should be clean, securely mounted, and not cracked. You should be able to see the trailer sides and the area immediately behind the vehicle.

Walk-Around Inspection

The walk-around is the heart of the pre-trip. Start at the driver's door and work your way around the vehicle systematically, checking every visible component:

• Frame and body: Check the frame for cracks, bends, or rust damage. Look at body panels for damage that could affect safety. Check that mud flaps are present and in good condition.
• Fuel tanks: Verify fuel level, check caps for secure fit, and look for leaks around tanks and lines.
• Exhaust system: Check for leaks, loose clamps, or broken hangers. Exhaust should not be routed near fuel lines or wiring.
• Air lines and electrical cords: Inspect all visible air lines for cracks, abrasion, or leaks. Listen for audible air leaks. Check electrical connections for damage or corrosion.
• Suspension: Check leaf springs for cracks, missing leaves, or shifted spring assemblies. Inspect air bags (if equipped) for leaks or damage. Check shock absorbers for leaks and secure mounting.
• Brake components: Visually inspect brake drums for cracks, brake linings for visible thickness, brake chambers for secure mounting, and slack adjusters for proper adjustment. Push rods should not extend more than one inch when brakes are applied.
• Drive shaft: Check for secure connections, missing balance weights, and excessive play in U-joints.
• Landing gear: On the trailer, ensure the landing gear is fully raised and the handle is secured. Check for bent or damaged support legs.

Tires and Wheels

Tire and wheel problems are among the leading causes of roadside breakdowns and DOT violations. Check every tire on the vehicle:

• Tread depth: Minimum tread depth is 4/32 of an inch on the front (steer) tires and 2/32 on all other tires. Use a tread depth gauge or the built-in wear indicators.
• Tire condition: Look for cuts, bulges, separations, and sidewall damage. Check for objects embedded in the tread (nails, screws, glass). Sidewall bulges indicate internal damage and are an immediate out-of-service condition.
• Air pressure: Check tire pressure with a gauge (or at minimum, thump tires with a tire billy and listen for the solid, consistent sound of properly inflated tires). Mismatched pressure between duals causes uneven wear and potential blowouts.
• Lug nuts: Check that all lug nuts are present and appear tight. Look for rust trails radiating from lug nuts, which indicate looseness. Missing lug nuts are an out-of-service condition if more than one is missing per wheel.
• Wheel seals and hubs: Check for oil or grease leaks around hub seals. A leaking hub seal can lead to bearing failure.
• Valve stems: Ensure valve stems are present, not cracked, and have caps installed.
• Matching duals: Dual tires should be properly matched in size and tread depth. A significant size difference between duals causes excessive wear on the larger tire.

Coupling System (Class A)

For Class A CDL drivers pulling a trailer, the coupling system requires careful inspection:

• Fifth wheel: Check that the fifth wheel is securely mounted to the frame with no missing bolts. The platform should not be cracked or damaged. Verify there is adequate grease on the fifth wheel plate.
• Locking jaws: Visually confirm that the locking jaws are closed around the trailer kingpin. The release handle should be in the locked position and the safety latch should be engaged.
• Kingpin: The kingpin should not be bent, cracked, or excessively worn.
• Air lines (gladhands): Check that the air line connections (gladhands) are properly seated, locked, and not leaking air. The emergency (red) and service (blue) lines should be correctly connected to their respective couplers.
• Electrical connection: The 7-way electrical cord should be firmly plugged in and secured. Check for damaged insulation or corroded pins.
• Slide mechanism: If the fifth wheel slides, check that the locking pins are fully engaged and the release handle is in the locked position.
• Tug test: Gently pull against the trailer with the tractor in a low gear to verify the coupling is secure. The trailer should not separate or show movement at the fifth wheel.

Trailer Inspection

The trailer inspection covers the same components as the tractor walk-around, plus trailer-specific items:

• Trailer body: Check for damage to the roof, sides, and floor. Look for holes, cracks, or shifted panels. On reefer trailers, check the refrigeration unit operation and fuel level.
• Doors: Rear doors should open and close freely. Check hinges, latches, and seals. For roll-up doors, check the door track and lifting mechanism.
• Trailer tires and wheels: Apply the same tire inspection standards as the tractor. Check all tires on both sides for tread depth, condition, pressure, and lug nuts.
• Trailer brakes: Inspect brake drums, linings, chambers, and slack adjusters on all trailer axles. Apply the trailer hand brake and check that the brakes engage properly.
• Trailer suspension: Check leaf springs or air ride suspension components for damage, leaks, or looseness.
• Trailer lights: Verify all marker lights, clearance lights, brake lights, and turn signals on the trailer are functioning. Check reflective tape for damage or missing sections.
• Landing gear: Confirm the landing gear is fully raised and the crank handle is stowed. Check for bent legs or damaged gears.
• Cargo securement: If loaded, verify the cargo is properly secured with adequate tie-downs, blocking, and bracing as required. Check that load does not exceed weight limits.

What CDL Testers Look For

During the CDL skills test, the pre-trip inspection is scored on your thoroughness and knowledge. Here is what examiners expect:

• Systematic approach: Follow a consistent, logical order. Start at one point and work your way around without skipping back and forth. Examiners want to see an organized method.
• Verbal explanation: For each component you check, explain what you are looking at, what the correct condition should be, and what defects would concern you. Do not just point and say "tire" -- say "I am checking the steer tire for tread depth, which must be at least 4/32 of an inch. I am looking for cuts, bulges, and sidewall damage."
• Touch and look: Actually touch components where appropriate (tug on lug nuts, push brake chamber push rods, wiggle hoses). Visual-only checks are not enough for some items.
• Under-vehicle checks: You are expected to get down and look under the vehicle at suspension, brakes, drive shaft, and frame components. Do not skip this because it is inconvenient.
• Air brake tests: Demonstrate the proper sequence: build air to full pressure, perform the static and applied air leakage tests, test the low air pressure warning, and test the spring (parking) brakes.
• Know your numbers: Be able to state specific measurements: minimum tread depths (4/32 front, 2/32 other), maximum steering wheel play (10 degrees), governor cut-out pressure (120-145 psi), and leakage rate limits (3 psi/min single, 4 psi/min combination).

For study resources on the knowledge test portion, see our CDL Practice Test Guide and 14-Day Study Plan. For the full CDL process overview, start with How to Get a CDL.

Frequently Asked Questions