Front of vehicle, engine area and steering axle

Now you leave the cab. With the engine OFF you check the front lenses, fluid levels, leaks and the steering system. Then you inspect one axle in detail: tires, rims, lug nuts, suspension, brake lines and brake contamination. On a real trip, every axle gets the same check.

Front lenses, fluid levels and leaks (engine off)

Lenses: light lenses or covers on the front must be the proper color, clean, not broken and not missing, so the lights can work properly.

Critical fluid levels: correct levels keep the engine, cooling, steering and brake systems working and make them last longer. With the engine off, say you would check:

• engine oil (lubricates the engine);
• coolant (cools the engine);
• power steering fluid (helps turn the front wheels);
• brake fluid — hydraulic brakes only.

Show where each dipstick or sight glass is, and say the level must be between the "add" and "full" marks. Caution: never remove the radiator cap when the engine is hot.

Fluid and air leaks: a leak can show a failing part you cannot easily see, like the transmission, fuel system or air compressor. Look for puddles on the ground, drips on and under the engine and transmission, and check hoses and air lines for condition and leaks.

Say: I'm checking that the engine oil is between the add and full marks on the dipstick.

Steering system

Worn, cracked, loose or broken steering parts can make you lose steering. Play (movement) in the linkage makes the vehicle wander or causes other serious control problems.

• The power steering box is securely mounted and not leaking.
• Steering hoses and connections are not cracked, worn or leaking.
• The links, arms and rods you can see between the steering box and the wheel show no wear or cracks; joints and sockets are not worn or loose.
• No missing nuts, bolts or cotter pins (cotter keys) in the steering connections.

Say: I'm checking that the steering box is properly mounted and secured and not leaking, and there are no missing nuts, bolts, or cotter pins.

Tires

Why: an underinflated tire flexes more and builds heat, so it can blow out. An overinflated tire is damaged more easily by curbs and potholes and has less tread touching the road, so less traction. Low tread makes hydroplaning more likely, lowers traction and increases stopping distance. Cuts and bulges can cause sudden tire failure and loss of control.

• Inflation: check pressure with a tire gauge. All valve stems must be reachable. Kicking the tires or hitting them with a mallet gets no credit — you must mention the tire gauge.
• Condition: no cuts or damage that expose the body plies in the tread or sidewall; valve caps present; valve stems not damaged or broken; no bumps or bulges in the sidewall; no mismatched sizes in dual tires.
• Tread depth: measure with a tread depth gauge in the major grooves that have wear bars: at least 4/32 inch on steering axle tires and 2/32 inch on all other tires.

If the tires have an automatic tire inflation system (ATIS) or a TPMS with hoses connected to the valve stems, just say the pressure is monitored and adjusted by an automatic system, and check that the system is working.

Say: I would check the air pressure with a tire gauge. I'm checking for at least 4/32 inch of tread on the steer tires, and no cuts, bulges, or exposed cords.

Rims and lug nuts

Rims: a damaged rim can lose its tire, lose air, let the wheel come off the axle, or let the tire come off a damaged flange or split rim — and you can lose control.

• No damaged, cracked or bent rims. Rims may not have welding repairs.
• On a wedge-type wheel, look for rust trails, which can mean the rim is loose.
• Bolt holes must not be elongated (stretched out of round).

Lug nuts: loose or missing lug nuts can make a wheel fall off.

• All lug nuts are present.
• None are loose; no rust trails or shiny threads that show looseness.
• No bent, broken or missing studs.

Say: I'm checking that all lug nuts are present and tight, with no rust trails or shiny threads.

Suspension: springs, mounts, U-bolts, air bags, shocks

Springs soak up the bumps of the road. U-bolts and mounting bolts hold the suspension to the axle. Air bags work with springs or replace them. Shocks cushion and steady the vehicle.

Why: broken or missing springs can drop the vehicle onto its frame or a tire and cause loss of control or a rollover. A shifted spring can hit a tire (blowout) or interfere with steering. Loose or broken U-bolts can cause loss of control or rollover. Bad air bags or shocks hurt handling and stopping distance.

Inspect, where visible and reachable:

• No missing, shifted, cracked or broken leaf springs; spring mounts not cracked, broken or missing parts.
• No broken or distorted coil springs; their mounts are not cracked or broken and have no missing parts.
• U-bolts and mounting bolts are not broken, missing or loose.
• Air ride suspension (if equipped) is secure, not damaged, not leaking.
• Shock absorbers (if equipped) are secure, not damaged, not leaking.
• The vehicle sits level both side to side and front to back.

On vehicles where these parts cannot be seen (such as transit or motor coach buses), tell the examiner, check that the vehicle sits level, and explain that a leaning vehicle may mean a suspension problem.

Brake lines, hoses and brake contamination

Brake lines carry air or hydraulic fluid to the wheel brakes. Losing hydraulic fluid can mean loss of braking power; losing air pressure can cause wheel lockup.

• Hoses and lines can supply air or fluid to the brakes and are not leaking.
• No cracked, worn or frayed hoses or lines.
• All hose and line couplings and fittings are secure.
• With electric brakes, check that the electric lines are secure and the casing is not worn or cracked.

Brake contamination: grease, oil or other material on the brakes lowers braking friction (which can cause a crash) and can be a fire hazard. If you can reach them, check the brake linings or pads and the drum or disc for grease, oil and similar contaminants.

Say: I'm checking that the brake hose is not cracked, worn, or frayed, is not leaking, and the fittings are secure.

Put it into practice

Educational questions with explanations. The answer review also works without the interactive quiz.