Vehicle Inspection: The Pre-Trip Walk-Around for a Tractor-Trailer
The Vehicle Inspection portion of the Missouri skills test asks you to perform a pre-trip inspection on a combination vehicle and say out loud what you are checking and why. The examiner scores whether you find and explain defects, not whether you recite a list.
The walk-around, in order
- Paperwork and overall condition; look for fresh leaks under the unit.
- Engine compartment: oil, coolant, power-steering fluid, washer fluid, belts and hoses, battery secured, exhaust system intact.
- Lights and reflectors: headlights high and low, four-way flashers, turn signals, brake lights, clearance lamps, side markers, reflectors, mud flaps.
- Brakes and air system.
- Coupling system: fifth wheel, kingpin, air lines, electrical cable.
- Suspension and undercarriage: springs, hangers, shocks, brake chambers, push rods, slack adjusters, rims, tires.
- Cargo securement.
Air brake checks
- Build to governor cut-out (about 120–125 psi), shut the engine off, release the brakes, wait one minute: leakage must not exceed 3 psi for a single vehicle or 4 psi for a combination.
- Apply and hold the foot valve and repeat the one-minute check with the same limits.
- Fan off pressure to confirm the low-air warning activates by 60 psi and the spring brakes set between 20 and 45 psi.
Worked example
In the applied leakage test on a combination, the gauge falls from 90 to 85 psi in one minute. Five psi exceeds the 4 psi limit, so the unit is defective and should be written up rather than road-tested.
Traps that cost marks
Naming parts without stating the defect; skipping slack adjusters and push rods; ignoring the fifth wheel during the walk-around; failing to mention the low-air warning and spring brake check; recapped tires on a steering axle.