Pre-trip inspection parts

Small side and corner lights that outline a vehicle's size at night.

Side marker lights run along the trailer. Clearance lights sit at the top corners. Front and side ones are amber; the rear ones are red.

The front glass of the cab that the driver looks through.

Check it for cracks, dirt, and stickers that block your view. Keep it clean inside and out, because dirt glares at night. Clear ice and snow before you drive.

Arms with rubber blades that sweep rain and snow off the windshield.

Check the arms for spring tension and the blades for stiff or torn rubber. The washer must spray and have fluid. If the wipers fail in bad weather, stop safely and fix them.

The hinged cover over the engine at the front of a truck.

You raise it, or tilt the whole cab, to check the engine compartment. Secure loose items first. Lower and latch it before you drive.

Few questions name the hood; they ask what to inspect at the front of the vehicle and in the engine compartment.

Side-mounted glass showing the driver traffic beside and behind the vehicle.

Adjust them before every trip, with the trailer straight, so each shows a bit of your vehicle. Check them often but briefly. Convex mirrors show more but make things look small and far.

A curved mirror that gives a wider view than a flat mirror.

Most trucks and buses have a small round mirror under the big flat one. It is convex, so you see more of the road beside you. Objects in it look smaller and more distant than they are.

The front lights that light the road and make the vehicle visible.

Headlights have low beams and high beams. On the pre-trip you check them from outside the vehicle: lenses clean, correct color, both beams working.

Flashing lights that tell other drivers you will turn or change lanes.

Front turn signals are amber or white; rear ones are red, yellow, or amber. The same lamps usually work as the four-way flashers.

The bar across the front of the vehicle that takes minor impacts.

On the pre-trip you check that the bumper is secure, not loose or hanging, and has no missing parts. The guard at the rear of a trailer is the DOT bumper, a separate item.

The registration plate that identifies the vehicle to police and inspectors.

The plate must be present, clean, readable, and firmly attached. Any registration sticker on it must be current.

Oil, fuel, coolant, or other liquid escaping from the vehicle.

Look under the vehicle for fresh puddles and at the underside of the engine and transmission for drips. Any leak must be found and fixed before you drive.

The rubber casings on the wheels that grip the road.

On the pre-trip you check inflation with a gauge, tread depth in the major grooves, and look for cuts, bulges, and damaged valve stems. Steering tires need deeper tread than the others. In very hot weather, stop and check the tires every two hours or every 100 miles.

Not the same as: A tire is the rubber part only; the metal part it sits on is the rim.

The metal wheel part that the tire is mounted on.

Check rims for cracks, bends, and welding repairs. Rust streaks around the nuts can mean the wheel is loose.

Not the same as: The rim is the metal part only; the tire is the rubber.

The nuts that hold the wheel on the hub studs.

All lug nuts must be present and tight. Rust trails or shiny metal around a nut can mean it has worked loose.

The seal that keeps lubricant inside the wheel hub around the bearings.

Look at the hub cap and the inside of the wheel. Oil or grease running out means the seal is leaking. Many hubs have a sight glass to check the oil level.

The small tube on the wheel for checking and adding tire air.

Each valve stem needs a cap. Look for cuts, cracks, bends, and stems rubbing on anything. On dual wheels the stems must be reachable with a gauge.

The gap between two tires mounted side by side on one hub.

Dual tires must not touch each other or any part of the vehicle. Nothing may be stuck between them, such as rocks or debris. Both tires should be the same size.

The doors that close the cargo area of the trailer or truck.

Doors must open and close properly, latch securely, and have working hinges. Side doors must be closed and locked before you drive, with any required seals in place.

The steps you climb to enter the cab or reach the catwalk.

Steps must be solid, securely bolted, and clear of oil, grease, snow, and ice. Use three points of contact when you climb.

Not the same as: In a question, 'steps you should take' means actions, not the cab steps.

The tank that stores the vehicle's fuel, usually mounted on the frame.

Check that the tank is mounted securely, that the cap is tight, and that nothing leaks from the tank or its lines. Fuel on the pavement is a fire hazard and very slippery.

Not the same as: Air tanks and tank vehicles are different things; 'tank' alone in a question is usually not the fuel tank.

The heat exchanger that cools the engine coolant with air flow.

Check the coolant level and the hoses on the pre-trip. Never open a hot radiator cap; the system is under pressure and can burn you.

The drive belt that turns the air compressor from the engine.

Some compressors are gear-driven and have no belt. If there is a belt, check it for cracks, fraying, and correct tension. A loose belt cannot drive the compressor properly.

The small tank that holds the fluid for the power steering system.

Check the fluid level between the add and full marks, and look at the hoses for leaks. Low fluid makes steering heavy.

The gearbox that turns steering wheel motion into steering linkage movement.

Check that the box is securely mounted and not leaking, with no missing nuts or bolts. The power steering hoses connect to it.

The arms and rods that carry steering motion to the wheels.

The linkage includes the pitman arm, drag link, tie rod, and the joints between them. Nothing may be bent, loose, or cracked, and every nut needs its cotter pin.

The lever on the steering gear box that moves the drag link.

The pitman arm is the first link after the gear box. Check that it is not bent or cracked and that its nut and cotter pin are in place.

The rod that connects the pitman arm to the wheel's steering arm.

The drag link runs from the pitman arm to the steering knuckle. It must be straight, with tight joints and cotter pins in place.

No question targets the drag link directly; steering questions ask which parts belong to the system and what defects matter.

The rod that links the two front wheels so they steer together.

The tie rod runs across the front axle between the steering knuckles. Bent, loose, or broken tie rods are a listed steering defect.

The engine-driven pump that circulates coolant through the engine and radiator.

Check that the pump is securely mounted, its hoses are tight, and nothing leaks. If a belt drives it, check the belt too.

The belt-driven generator that charges the battery and powers the electrical system.

Check its mounting, wiring connections, and belt. Inside the cab, the ammeter or voltmeter shows whether the alternator is charging.

The amount of engine oil in the engine, read on the dipstick.

Pull the dipstick, wipe it, put it back, and pull it again. The oil should sit between the add and full marks.

The rubber hoses and electrical wires routed around the engine compartment.

Hoses must be attached, not cracked, and not leaking. Wiring insulation must not be cracked, worn, or frayed. Nothing should rub on moving or hot parts.

A hydraulic or gas damper that controls the bounce of the suspension.

Shocks sit beside the springs or air bags. Check that each one is securely mounted, not bent, and not leaking oil.

A stack of curved steel strips that carries the vehicle's weight.

Each strip is a leaf. Leaves must not be cracked, broken, missing, or shifted so they could hit a tire. If one-fourth or more of the leaves are missing or broken, the vehicle is out of service.

The brackets and U-bolts that fasten the springs to frame and axle.

Spring hangers hold the ends of the leaf spring to the frame. U-bolts clamp the spring to the axle. All must be present, tight, and not cracked.

The hoses and tubes that carry air or brake fluid to each brake.

Lines must be securely mounted and not leaking. Look for cracks, cuts, chafing, and fraying, and make sure every fitting is tight.

The storage battery that starts the engine and powers the electrical system.

Batteries may sit in the engine compartment or in a box on the frame. Check that they are secure, the connections are tight and clean, and the box cover is latched.

The metal platform behind the cab where the trailer lines connect.

The catwalk must be solid, bolted firmly to the frame, and kept clear of objects. Keep it free of oil, grease, snow, and ice.

Questions do not target the catwalk directly; on the inspection test you check it with the steps for mounting and clear footing.

The steel rails and cross members that carry the body, axles, and load.

Look for cracks, bends, broken welds, and holes in the frame rails and cross members. Illegal welds and missing bolts are also defects.

Not the same as: In a question, 'time frame' means a period of time, not the vehicle frame.

The spinning shaft that sends engine power to the drive axle.

Check the drive shaft for bends and cracks, and make sure the U-joints at each end are secure and free of debris.

Questions do not target the drive shaft directly; on the inspection test you check it for damage and secure joints.

The pipes and muffler that carry exhaust gases away from the cab.

Parts must be securely mounted, not leaking, and not touching fuel lines, wiring, or tires. A leak lets poison fumes reach the cab or sleeper.

The outside lamps and reflectors that make the vehicle visible to others.

Lights and reflectors must be clean, working, the correct color, and not broken or missing. Front and side ones are amber; rear ones are red.

Not the same as: Emergency reflectors (the triangles) are separate equipment, not the reflectors fixed to the vehicle.

Flaps behind the wheels that stop tires from throwing mud and water.

Also called mud flaps. They must be present, not torn, properly mounted, and not dragging on the ground or rubbing the tires.

A suspension arm that links the axle to the frame and guides it.

Control arms and their mounts must be securely attached and not bent, cracked, or broken. They are suspension parts, not steering parts.

Not the same as: A control arm is suspension; it does not steer the wheels.

A suspension rod that locates the axle and resists twisting forces.

On trucks the inspection item is usually the torque rod, also called a radius rod, that keeps the axle in place. Check that it is securely mounted and not bent, cracked, or broken.

Questions do not target this part directly; suspension questions ask which axle positioning parts must not be cracked, damaged, or missing.

Not the same as: Here it usually means the torque rod that locates the axle, not a car's torsion-bar spring.

Rubber bellows filled with compressed air that act as the vehicle's springs.

Air ride suspension uses air bags instead of, or together with, steel springs. Check that each bag is securely mounted, not damaged, and not leaking; listen for hissing.

Not the same as: Not the safety airbags in a steering wheel; these are suspension parts.

The tractor frame structure that holds the fifth wheel skid plate.

Check the platform for cracks, breaks, and loose or missing mounting bolts. It must hold the skid plate solidly.

Questions do not target the platform directly; fifth wheel questions ask what to check on the coupling before and after hooking up.

The greased fifth wheel plate that the trailer apron rests on.

The skid plate must be securely mounted on the platform, properly greased, free of cracks, and able to tilt freely. The kingpin locks into it.

Any space between the trailer apron and the fifth wheel after coupling.

After coupling, look between the apron and the skid plate. The trailer should lie flat on the fifth wheel with no space. Any gap means the coupling is wrong.

Straps or hooks that hold trailer doors shut, or hold them open.

On the pre-trip, ties must be present, not broken, and securely mounted. A loose door swinging at speed can hit other vehicles.

Questions do not target door ties directly; door questions ask about latching and about seals on sealed loads.

Not the same as: A door seal is different: the rubber weather seal, or the numbered security seal on a locked load.

The rear guard that stops a car from sliding under the trailer.

Also called the ICC bumper or rear impact guard. Check that it is securely mounted and not bent, broken, or damaged.

Questions do not target the DOT bumper directly; on the inspection test you name it at the rear and check its condition.

The safety items a commercial vehicle must carry for breakdowns and fires.

The required set is a fire extinguisher, spare electrical fuses unless the vehicle has circuit breakers, and warning devices for a stopped vehicle. Tire chains and an accident kit are optional extras.

A portable device for putting out small fires, carried in the cab.

Check that it is fully charged, the gauge is in the green, the pin and seal are in place, and it is mounted securely. The rating letters tell you which fire classes it handles. A power unit carrying placarded hazardous materials must have an extinguisher rated at least 10 B:C.

Extra electrical fuses carried to replace a blown fuse on the road.

Required unless the vehicle uses circuit breakers. On the inspection test, say so if your vehicle has breakers instead of fuses.

Reflective triangles or flares that warn traffic your vehicle is stopped.

Carry three red reflective triangles; set them out within 10 minutes of stopping and hold each one toward traffic as you walk. On a one-way or divided highway, space them 10, 100 and 200 feet behind the vehicle, toward the traffic. On a two-lane road, put one within 10 feet of the vehicle, one 100 feet behind and one 100 feet ahead.

The belt that holds you in your seat during a crash.

Federal rules require you to wear the seat belt whenever you drive a commercial motor vehicle. On the pre-trip, check that it is mounted securely, adjusts, latches, and is not ripped or frayed.

Pedal that disconnects the engine from the transmission so you can shift gears.

Press it with your left foot before you move the shifter, then let it out smoothly. Most heavy trucks need double clutching: press, shift to neutral, release, press again, shift into gear. On the in-cab check you make sure it is not loose, sticking or damaged.

The pedal that controls engine power; pressing it speeds the truck up.

Drivers also call it the gas pedal. Press it gently so the truck does not jerk; on wet or icy roads too much power makes the drive wheels spin. If the truck's retarder is switched on, letting the pedal all the way up makes the retarder brake.

The lever you move to select a gear in a manual transmission.

Before you start the engine, put the shifter in neutral, or in park on an automatic. On trucks with extra gear ranges, a selector knob or switch on the shifter changes range.

Dash gauge showing how hot the engine coolant is.

After you start the engine, the needle should rise slowly into the normal range and stay there. A reading that keeps climbing means the engine is overheating; stop and find the cause.

Dash gauge showing the pressure of the oil circulating through the engine.

The needle should move into the normal range within seconds of starting the engine. If it stays low or a warning light stays on, shut the engine off; running without oil pressure destroys it.

Dash gauge showing whether the alternator is charging the batteries.

An ammeter shows current flowing in or out of the batteries; a voltmeter shows system voltage. After start-up the needle should sit in the normal range and the charging warning light should go out.

No current question stem uses the term; it appears among the gauges checked after start-up and during the trip.

Dashboard lights that show which lamps are on: turn signals, four-way flashers, high beams.

In the vehicle inspection test you name each indicator and show it works when you switch the lamp on. The ABS light and, on some trucks, the DEF light are checked in the same step.

No current knowledge-test stem uses the term; it is a named item in the in-cab part of the vehicle inspection test.

The electric or air-powered device that sounds a warning to other road users.

Use the horn when it helps avoid a crash, for example a light tap before passing someone who may not see you. Do not use it to vent anger; a sudden blast can startle other drivers and cause the crash you wanted to avoid.

Not the same as: In coupling text, the horn of a pintle hook is a metal lug, not the warning device.

Cab controls that warm the driver and clear frost or fog from the windshield.

In the inspection test you turn the switch from heat to defrost and show both work. In winter, check them before you leave; if you cannot see out, you cannot drive safely.

Depth of a tire's main grooves; shallow grooves mean less grip.

Front (steering) tires need at least 4/32 inch of tread in every major groove; all other tires need at least 2/32 inch. No fabric may show through the tread or sidewall. Measure with a tread depth gauge in every major groove; on the inspection test, say that you use a gauge.

Free movement of the steering wheel before the front wheels respond.

A little play is normal. Too much play makes the truck hard to steer and means worn or loose steering parts; it must be fixed before you drive. The manual gives the limit in degrees and in inches of movement at the rim.

Timed air-pressure drop with the engine off and all brakes released.

Build full air pressure, shut the engine off, release the parking brakes, wait for the gauge needle to settle, then time one minute. If pressure drops more than the manual allows, there is a leak to find before you drive. The allowed loss is in the air leakage rate entry.

Not the same as: Not the applied test: here the brake pedal stays up; the applied test holds it down.

Air-pressure drop timed while the brake pedal is held fully down.

With the engine off and parking brakes released, press the brake pedal all the way, let the gauge settle, then hold for one minute. The allowed loss is a little higher than in the static test; see the air leakage rate entry. It is one of the four air brake checks; missing any one fails the vehicle inspection test.

Fanning air pressure down until the parking-brake valve pops out on its own.

With the engine off, pump the brake pedal to bleed air down. First the low-air warning should come on; keep pumping and the yellow and red knobs should pop out, which sets the spring brakes. The pressure range where this must happen is in the spring brake pop-out range entry.