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CDL General Knowledge Test: Vehicle Inspection Concepts
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Overview
This chapter covers why commercial drivers inspect their vehicles, what defects to look for, and how to do an inspection the same way every time. Federal and state laws require drivers to inspect their vehicles, and inspectors can put an unsafe vehicle out of service until it is fixed.
There are three kinds of inspection. The pre-trip inspection finds problems before you leave. During the trip, you watch your gauges, use your senses, and check critical items such as tires, brakes, lights, trailer connections, and cargo securement whenever you stop. The after-trip inspection and report tell the motor carrier what needs repair.
The defects to know are specific. Front tires need at least 4/32 inch of tread in every major groove and other tires at least 2/32 inch. Steering wheel play of more than 10 degrees makes steering hard. Rust around wheel nuts may mean they are loose. You must also carry spare fuses (unless the vehicle has circuit breakers), three red reflective triangles, and a charged fire extinguisher.
Key concepts
Pre-trip inspection
A full check of the vehicle before driving, done in the same order every time so nothing is missed. Safety for you and others is the most important reason to do it.
Memory tipSame order every time means you do not forget a step.
Tire tread depth
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 should show through the tread or sidewall.
Memory tipFront 4, others 2 (in 32nds of an inch).
Source: New York State DMV Commercial Driver's Manual (CDL-10), Section 2 · as of 2026
Steering wheel play
Free movement of the steering wheel before the wheels turn. More than 10 degrees, about 2 inches at the rim of a 20-inch wheel, can make the vehicle hard to steer.
Memory tip10 degrees is about 2 inches at the rim.
Source: New York State DMV Commercial Driver's Manual (CDL-10), Section 2 · as of 2026
Required emergency equipment
Spare electrical fuses (unless the vehicle has circuit breakers), three red reflective warning triangles, and a properly charged and rated fire extinguisher.
Memory tipFuses, three triangles, and an extinguisher.
Source: New York State DMV Commercial Driver's Manual (CDL-10), Section 2 · as of 2026
Hydraulic brake leak test
Pump the brake pedal three times, then press firmly and hold for five seconds. If the pedal moves, there may be a leak or other problem. Get it fixed before driving.
Memory tipPump three, hold five, pedal should not move.
Out-of-service spring defects
A vehicle is put out of service if one-fourth or more of the leaves in any spring assembly are broken, if any leaf is missing or separated, or if any main leaf is broken.
Memory tipA quarter of the leaves broken is too many.
Source: New York State DMV Commercial Driver's Manual (CDL-10), Section 2 · as of 2026
Often tested
- Safety is the most important reason to inspect your vehicle.
- Front tires need at least 4/32 inch of tread. Other tires need at least 2/32 inch.
- Recapped, regrooved, or retreaded tires are not allowed on the front wheels of a bus.
- Oil pressure should come up to normal within seconds after the engine starts.
- At each stop during a trip, check tires, wheels, rims, brakes, lights, trailer connections, and cargo securement.
3 sample questions
Verified practice questions from this unit.
Question 1. What is the minimum tread depth for the front (steering) tires of a truck?
- ① 2/32 inch in every major groove
- ② 4/32 inch in every major groove
- ③ 1/32 inch in every major groove
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Answer: ② 4/32 inch in every major groove
Key point: Front tires 4/32 inch, other tires 2/32 inch
Front tires need at least 4/32 inch of tread depth in every major groove. All other tires need at least 2/32 inch. Front tires need more tread because they steer the vehicle.
Wrong choices
- 2/32 inch in every major groove: 2/32 inch is the minimum for the other tires, not the front tires.
- 1/32 inch in every major groove: This is far too little tread for any tire on a commercial vehicle.
Question 2. Which set of emergency equipment must a commercial vehicle carry?
- ① A spare tire, tire chains, and a flashlight
- ② A first-aid kit, a jack, and a road map
- ③ Spare fuses (unless it has circuit breakers), three red reflective triangles, and a charged fire extinguisher
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Answer: ③ Spare fuses (unless it has circuit breakers), three red reflective triangles, and a charged fire extinguisher
Key point: Fuses, 3 triangles, fire extinguisher
The required emergency equipment is:
- Spare electrical fuses (unless the vehicle has circuit breakers)
- Three red reflective warning triangles
- A properly charged and rated fire extinguisher
Wrong choices
- A spare tire, tire chains, and a flashlight: Chains and tire-changing tools are optional items, not the required set.
- A first-aid kit, a jack, and a road map: These can be useful, but they are not the required emergency equipment.
Question 3. What is the most important reason to inspect your vehicle?
- ① Safety for you and other road users
- ② To avoid paying for repairs
- ③ To keep the vehicle looking clean
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Answer: ① Safety for you and other road users
Key point: Inspections are mainly about safety
Safety is the most important reason to inspect your vehicle. A defect you find before the trip can prevent a breakdown or a crash. Federal and state laws also require drivers to inspect their vehicles.
Wrong choices
- To avoid paying for repairs: Finding problems early can save money, but cost is not the main reason.
- To keep the vehicle looking clean: Inspections look for defects, not dirt.