Vehicle Inspection for Combination Vehicles
Vehicle inspection - what the Combination test asks
The Combination test treats inspection as a combination-specific skill: you must know the seven-step walkaround and the extra items that exist only when a tractor pulls a trailer - fifth wheel, kingpin, air lines, electrical cord, landing gear, and trailer frame.
The seven steps, in order
- Vehicle overview and paperwork; look for missing or damaged parts and leaks.
- Engine compartment: fluids, belts, hoses, steering, exhaust.
- Start the engine and inspect inside the cab: gauges, controls, horn, wipers.
- Check lights and reflectors.
- Check brakes and the air system.
- Walk-around: tires, wheels, rims, hubs, suspension, frame, doors.
- Signal and brake lights, then the final air-brake test.
Combination-only items
- Fifth wheel: jaws closed around the kingpin, release handle in and latched, no gap between the trailer apron and the fifth wheel plate, mounting bolts tight, plate greased.
- Air and electrical: glad-hand seals intact, lines not crossed or chafed, cord with enough slack to turn, secured so it cannot drag.
- Landing gear fully raised, crank handle in its holder, no leaks at the couplers.
The leakage test
Engine off, tanks at 90 psi, brakes released: no more than 3 psi lost in one minute. Brakes fully applied: no more than 4 psi in one minute. A single non-combination vehicle gets 2 and 3 psi. A popped tractor protection valve or a leaking glad-hand shows up here.
Worked example
At 90 psi with the engine off and a full brake application held, the gauge drops 5 psi in one minute. The combination limit is 4 psi/min, so this rig fails the test and cannot be dispatched until the leak is found - usually a coupler seal, a trailer hose, or a spring-brake chamber. The reasoning is the limit comparison, not the gauge reading alone.
Traps
- Mixing the single-vehicle 2/3 psi limits with the combination 3/4 psi limits.
- Looking at the fifth wheel instead of confirming jaw position and the gap.
- Forgetting the low-air warning must sound before 60 psi.
- Skipping the tug test after coupling.