Commercial Driver's License (CDL) Vehicle Inspection, Maintenance, and Control Systems Syllabus

Why should you never remove a radiator cap on a hot engine?

The cooling system is pressurized; removing the cap when hot can cause scalding coolant and steam to spray out. Wait until the engine cools, or check the overflow/sight glass instead.

What gauges should be monitored for the engine oil and coolant systems while driving?

Oil pressure gauge (should read in the normal range shortly after startup), coolant temperature gauge (should stay in the normal operating range), and the voltmeter/ammeter for the charging system.

What does a sudden drop in oil pressure while driving indicate?

A serious problem (loss of lubrication). The driver should stop safely as soon as possible and shut off the engine to prevent severe engine damage.

What steering system components must be inspected, and what are you looking for?

Steering box (securely mounted, no leaks, no missing bolts), steering linkage (tie rods, drag links, arms—no worn, cracked, bent, or loose parts), power steering hoses for leaks, and the steering wheel for excessive free play.

How much steering wheel free play is excessive on a vehicle with power steering?

More than about 10 degrees of play (roughly 2 inches of movement on a 20-inch wheel) before the wheels move indicates a steering system problem.

What suspension components should be inspected during a pre-trip?

Springs and spring hangers (no cracked, broken, shifted, or missing leaves), shock absorbers (no leaks or damage), U-bolts and other axle mounting parts, torque rods, and air suspension (no leaks, properly inflated air bags).

What is a defect in a leaf spring that would put a vehicle out of service?

A broken or missing leaf, or a cracked/broken spring hanger; any condition that allows the axle to shift or the spring to contact a tire or moving part.

What must you inspect on the exhaust system?

Mufflers, pipes, and connections for leaks, looseness, broken or missing mounting brackets, and that no exhaust components contact fuel lines, tires, or other moving parts. Leaking exhaust can let toxic carbon monoxide into the cab.

Why is an exhaust leak a serious safety hazard?

Exhaust contains carbon monoxide, a colorless, odorless, poisonous gas. A leak can allow it to enter the cab, causing illness or death, and is a fire risk near fuel lines.

What should you check when inspecting the vehicle frame?

Look for cracks, bends, rust streaks (indicating cracks), broken or missing crossmembers, and loose, broken, or missing bolts or rivets in the frame, body, and cab mounts.

What is the minimum legal tread depth for the front (steer) tires of a commercial vehicle?

4/32 of an inch of tread depth in every major groove on front tires.

What is the minimum legal tread depth for tires other than the front steer tires?

2/32 of an inch of tread depth in every major groove on all other tires.

What are the recommended methods for checking tire air pressure?

Use a tire pressure gauge—do not rely on thumping or kicking. Check pressure when tires are cool for an accurate reading; underinflation and overinflation are both unsafe.

List tire defects that make a tire unsafe to drive.

Too little tread, fabric or body cords showing, cuts or other damage exposing the cord, tread or sidewall separation, bulges/bumps, audible or felt air leaks, mismatched sizes, and recapped tires on the front (steer) axle of a bus.

Why must dual tires not touch each other or other parts?

Touching duals or a tire rubbing another part generates heat and friction that can cause tire failure or fire, and signals improper inflation or mounting problems.

What wheel and rim defects should you look for?

Cracked or damaged rims, rust trails around lug nuts (indicating looseness), missing or loose lug nuts/clamps/studs, bent or damaged wheels, and cracks across or between hand holes. Welded or repaired wheels are not safe.

What does a rust trail or shiny streak around wheel lug nuts indicate?

That the lug nuts are loose. Loose lugs can allow the wheel to come off and must be corrected before driving.

What lights and reflectors must a commercial vehicle have working, and what colors?

Required: clearance lights, identification lights, marker lights, taillights, brake lights, turn signals, headlights, and reflectors. Front-facing are white/amber; rear-facing are red; reflectors are usually red (rear) and amber (side).

What should you check about the electrical system during inspection?

Battery is secure and connections are tight and not corroded, no exposed or frayed wires, no signs of overheating, and that all lights and electrical accessories function. Check the voltmeter for proper charging while running.

What is the smooth way to accelerate a commercial vehicle?

Press the accelerator gradually and smoothly to avoid jerking. Speed up gently so the drive wheels do not spin, especially on slippery surfaces, and to protect the drivetrain.

What can happen if you accelerate too quickly on a slippery surface?

The drive wheels can lose traction and spin, causing the rear of the vehicle to slide (a drive-wheel skid) and loss of control.

What are the two basic steering rules for smooth control?

Hold the wheel firmly with both hands on opposite sides (about 9 and 3 o'clock) and turn smoothly. Avoid jerking the wheel; sudden movements at speed can cause loss of control or rollover.

What is the difference between controlled braking and stab braking?

Controlled braking applies steady, firm pressure without locking the wheels (used to slow while keeping steering control). Stab braking applies the brakes fully, releases when wheels lock, and reapplies—used in emergencies on vehicles without ABS.

What is the proper technique for backing a commercial vehicle safely?

Back slowly using the lowest reverse gear, back toward the driver's (left) side when possible for visibility, use a helper/spotter, get out and look (G.O.A.L.) before backing, and use mirrors and the horn to signal.

Why should you back toward the driver's side when possible?

Backing toward the left (driver's) side lets you see down the side of the vehicle through your window and mirror, giving better visibility and control than blind-side (right) backing.

What is total stopping distance and what are its components?

Total stopping distance = perception distance + reaction distance + braking distance. It is the total distance from seeing a hazard to the vehicle coming to a complete stop.

How does speed affect braking distance?

Braking distance increases with the square of speed. Doubling your speed (e.g., 20 to 40 mph) roughly quadruples the braking distance, dramatically increasing total stopping distance.

What is the correct method to select the right gear when shifting up in a manual transmission?

Use the engine speed (rpm) and road speed. Shift up when the engine reaches the top of its rpm range; release the accelerator, push in the clutch and shift to neutral, release the clutch, let rpm drop, then push the clutch and shift into the higher gear.

What is double-clutching and why is it used?

Double-clutching is shifting by pushing the clutch to move to neutral, releasing it, then pushing it again to engage the next gear. It matches engine and transmission speeds for smooth shifting without grinding gears in non-synchronized truck transmissions.

When should you downshift in a manual transmission?

Before starting down a hill (to use engine braking) and before entering a curve—downshift while still on the level/straight, before you need the lower gear, so the vehicle is in the correct gear for control.

What is offtracking and which wheels follow a wider path in a turn?

Offtracking (cheating) is when the rear wheels of a vehicle follow a different, tighter path than the front wheels during a turn. The driver must swing wide enough so the rear wheels clear curbs and obstacles, while keeping the rear from striking objects.

How should you steer to keep a vehicle tracking straight, and what causes drifting?

Make small, smooth steering corrections and look far ahead to keep the vehicle centered in the lane. Drifting can be caused by crosswinds, road crown, uneven tire pressure, or steering/alignment problems; correct gently rather than overcorrecting.