CDL General Knowledge Test Vehicle Inspection Summary

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.

The required emergency equipment is:

1. Spare electrical fuses (unless the vehicle has circuit breakers)
2. Three red reflective warning triangles
3. 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.

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.

Rust around the wheel nuts may mean the nuts are loose. Check their tightness. After a tire has been changed, stop a short while later and check the nuts again.

Wrong choices

• The tire pressure is too high: Tire pressure does not cause rust around the wheel nuts.
• The wheel was recently replaced: Rust streaks do not show that a wheel is new.

Steering wheel play of more than 10 degrees is a defect. On a 20-inch steering wheel that is about 2 inches of movement at the rim. Too much play makes the vehicle hard to steer.

Wrong choices

• More than 5 degrees (about 1 inch at the rim): 5 degrees is less than the 10-degree limit, so it is not yet a defect.
• More than 30 degrees (about 6 inches at the rim): Play this large is far past the safe limit. The limit is much smaller.

To test hydraulic brakes for leaks:

1. Pump the brake pedal three times.
2. Press the pedal firmly and hold it for five seconds.
3. The pedal should not move. If it does, there may be a leak. Get it fixed before driving.

Wrong choices

• Press the pedal once lightly and see if the brake light comes on: This only checks the brake light, not leaks.
• Drive at highway speed and stop as hard as you can: This is unsafe and is not the leak test.

Regrooved, recapped, or retreaded tires are prohibited on the front wheels of a bus. A front tire failure is very dangerous because it can pull the steering wheel out of your hands.

Wrong choices

• Radial tires of the correct size: Radial tires are fine as long as you do not mix them with bias-ply tires.
• New tires with deep tread: New tires are what you want on the front wheels.

A vehicle is put out of service if:

1. One-fourth or more of the leaves in any spring assembly are broken,
2. any leaf or part of a leaf is missing or separated, or
3. any main leaf is broken.

Wrong choices

• When a spring leaf has light surface rust: Light rust alone is not an out-of-service defect.
• When the springs are covered with road dirt: Dirt is not a defect.

When you stop during a trip, check the critical items: tires, wheels, and rims; brakes; lights and reflectors; brake and electrical connections to the trailer; trailer coupling devices; and cargo securement devices. The radio and CB antenna are not on this list.

Wrong choices

• Tires, wheels, and rims: Tires, wheels, and rims are critical items to check at stops.
• Cargo securement devices: Cargo securement is a critical item to check at stops.

Oil pressure should come up to normal within seconds after the engine starts. If it is low, dropping, or jumping around, stop the engine right away. Without oil, the engine can be destroyed quickly. (Coolant and oil temperature are the gauges that rise slowly.)

Wrong choices

• Rise slowly over the first 10 to 15 minutes: Oil pressure that takes minutes to rise is a warning sign.
• Stay at zero until the vehicle starts moving: Zero oil pressure means no oil flow. Stop the engine right away.