Pre-Trip Inspection Step by Step — Pass the CDL Skills Test

Section 1 — Engine Compartment

Start at the front of the vehicle, raise the hood or open the engine compartment door. Verbally identify and check each item as you go:

• Engine oil level — should be at or near the full mark on the dipstick
• Coolant level — check the overflow reservoir (never open a pressurized radiator cap when hot)
• Power steering fluid — fill line indicator on the reservoir
• Windshield washer fluid
• Battery — secure, no corrosion, fluid at proper level (if non-sealed)
• Belts — check for fraying, cracking, or excessive slack (max ¾ inch deflection)
• Hoses — no cracks, leaks, or soft spots; check upper and lower radiator hoses
• Air compressor — mounted securely, no visible leaks in air lines
• Alternator/generator — secure, belt in good condition
• Wiring — no frayed or loose wiring near hot or moving parts
• Leaks under the vehicle — oil, coolant, fuel, or brake fluid on the ground

Say out loud: "I'm checking the oil level — it reads full, no leaks visible. Checking coolant level — at the operating range mark. Power steering fluid — full. All belts secure with proper tension..."

Section 2 — Cab Interior Check

Enter the cab and check all controls and safety equipment:

• Parking brake — set (pull the yellow knob), will release during air brake check
• Clutch / gearshift — moves freely through all positions
• Steering wheel — check for excessive play (no more than 10° for power steering)
• Air pressure gauge — should be in the normal range (100–125 psi)
• Warning lights and buzzers — turn key on, all lights should illuminate (oil, temp, ABS, airbag if equipped)
• Windshield — no cracks or obstructions in the driver's line of sight
• Wipers and washers — blades in good condition, washer functional
• Mirrors — properly adjusted, no cracks
• Horn — both city (electric) and air horn (if equipped)
• Heater/defroster — operates properly
• Emergency equipment — fire extinguisher (charged, correct rating), 3 red emergency triangles, spare fuses
• Seat belt — latches and adjusts properly

Section 3 — Lights Check

Walk around the entire vehicle and check all lights. On the skills test, you typically need a helper or use a wall/reflection. Check:

• Headlights — low and high beam
• Taillights and brake lights
• Turn signals (front and rear, both sides)
• 4-way hazard flashers
• Marker lights (amber on front, red on rear)
• Clearance lights (top corners of cab and trailer)
• Reflectors — clean and unbroken
• License plate light
• Side marker lights on trailer

All lights must be clean, operational, and the correct color for their position. Missing, cracked, or non-functional lights are scored defects.

Section 4 — Brake System Check

This is where the air brake inspection takes place (see our complete Air Brakes guide for details). Key steps:

• Check low pressure warning at 55 psi
• Check spring brake application at 20–45 psi
• Build pressure to 100–125 psi
• Static leakdown test (max 2 psi/min single, 3 psi/min combination)
• Applied leakdown test (max 3 psi/min single, 4 psi/min combination)
• Walk around and check each brake chamber — no oil, grease, or visible leaks
• Check brake hoses and connections — no cracks, kinks, or chafing
• Check brake drums — no cracks, no contact with axle seals
• Check brake lining visible through drum holes or with a flashlight — adequate thickness
• Check slack adjusters — all in line, properly adjusted

Section 5 — Tires and Wheels

Check every tire on every axle of the tractor AND the trailer:

• Tire pressure — visually check for obvious flats; use gauge if tester provides one; steer tires min 90–100 psi typically, drive tires min 75–95 psi (varies by rating)
• Tread depth — minimum 4/32" on steering axle tires, 2/32" on all others
• Condition — no cuts, bulges, exposed cords, or sidewall damage
• Dual tires — must not be touching each other or other components; valve stems accessible
• Lug nuts — all present, no rust streaks (indicates loose nuts), no damage
• Hub oil seals — check center of wheel hub for oil leaks (wet = defect)
• Rims — no cracks, no welds on aluminum rims, no damage
• Spacers/lock rings — present and properly seated on multi-piece rims

Section 6 — Suspension System

• Leaf springs — check for cracks, missing leaves, or shifted leaves
• Air bags/air ride — no leaks, properly seated, equal height side-to-side
• Shock absorbers — no leaks, mounted securely
• U-bolts and spring hangers — tight, no cracking
• Torque arm / radius rods — securely mounted, no play
• Axles — no visible cracks or bends

Section 7 — Coupling System (Tractor-Trailer Only)

This section is specific to Class A tractor-trailer combinations and is heavily scored:

• Fifth wheel — properly lubricated (greased), mounted securely to frame, no cracks in mounting plate
• Fifth wheel jaws — fully closed and locked around the kingpin
• Kingpin / locking jaw test — pull forward with brakes set to confirm the trailer does not separate ("tug test")
• Trailer height — trailer should rest on fifth wheel, not too high or low
• Air lines (glad hands) — blue (service) and red (emergency/supply) lines connected, no leaks, no kinks, mounted in proper holders when traveling
• Electrical connector (pigtail) — plugged in securely, no damage to cord
• Trailer brake lines — check under trailer, no dragging or chafing
• Landing gear — fully raised and locked, crank handle secured
• Sliding tandem — locked in position, pins fully engaged
• Safety catch — fifth wheel release handle in the locked position