Vehicle Inspection and Basic Control FAQ - Common Questions Answered

This FAQ guide answers the most common questions about vehicle inspection and basic control from Sections 2.1-2.3 of the CDL manual. Find quick answers about the 7-step inspection method, tire requirements, suspension defects, steering problems, backing rules, and shifting procedures that you'll encounter on the CDL exam.

Vehicle Inspection Questions

Q: What is the most important reason for doing a vehicle inspection?

A: Safety—for yourself and other road users. A vehicle defect found during inspection could prevent a breakdown or crash later. Federal and state laws require inspections, and inspectors can place unsafe vehicles "out of service" until fixed.

Q: What are the 7 steps of the vehicle inspection method?

A: The 7 steps are: (1) Vehicle overview—approach and check for leaks/damage, (2) Check engine compartment—fluids, belts, leaks, (3) Start engine and inspect inside cab—gauges, controls, emergency equipment, (4) Turn off engine and check lights, (5) Walk-around inspection—complete exterior check, (6) Check signal lights, (7) Start engine and check brakes.

Q: What three types of emergency equipment are required?

A: You must have: (1) spare electrical fuses (unless equipped with circuit breakers), (2) three red reflective triangles OR 6 fuses OR 3 liquid burning flares, and (3) a properly charged and rated fire extinguisher.

Q: What should the ABS indicator light do when you start the engine?

A: The ABS light should come on briefly and then turn off. If it stays on, the ABS is not working properly. For trailers, check the yellow light on the left rear—if it stays on, trailer ABS is malfunctioning.

Q: How do you test hydraulic brakes for leaks?

A: Pump the brake pedal three times, then apply firm pressure and hold for five seconds. The pedal should not move. If it moves, there may be a leak or other problem—get it fixed before driving.

Q: How fast should air pressure build up?

A: Air pressure should build from 50 to 90 psi within 3 minutes. Build to governor cut-out, usually around 120-140 psi. Know your specific vehicle's requirements.

Tire Questions

Q: What is the minimum tread depth for front tires?

A: Front tires require minimum 4/32 inch tread depth in every major groove. This is more than other tires because front tires are critical for steering.

Q: What is the minimum tread depth for other tires?

A: All tires except front (drive and trailer tires) require minimum 2/32 inch tread depth. No fabric should show through the tread or sidewall on any tire.

Q: Can you mix radial and bias-ply tires?

A: No. Radial and bias-ply tires should not be used together on the same vehicle. Mixing tire types causes handling problems.

Q: What tire defects should you look for?

A: Check for: too much or too little air pressure, bad wear patterns, cuts or damage, tread separation, dual tires touching each other or vehicle parts, mismatched sizes, cut or cracked valve stems, and fabric showing through tread or sidewall.

Q: Are retreaded tires allowed on the front of a bus?

A: No. Re-grooved, recapped, or retreaded tires are prohibited on the front wheels of a bus.

Suspension Questions

Q: What suspension defect puts a vehicle out of service?

A: If one-fourth or more of the leaves in any leaf spring are missing or broken, the vehicle is out of service. However, any suspension defect could be dangerous and needs attention.

Q: Why are suspension defects so dangerous?

A: The suspension system holds up the vehicle and its load while keeping axles in proper position. Broken suspension parts can cause loss of control because the axles may shift out of position.

Q: What suspension components should you check?

A: Check spring hangers (for movement allowing axle shift), springs (cracked, broken, or missing leaves), shock absorbers (leaking), u-bolts, torque rods, and air suspension components (damage and leaks).

Q: What does a leaking shock absorber indicate?

A: Leaking shock absorbers are defective and won't properly dampen vehicle movement. This affects handling and ride quality and should be reported for repair.

Steering Questions

Q: How much steering wheel play is acceptable?

A: Steering wheel play should not exceed 10 degrees, which is approximately 2 inches of movement at the rim of a 20-inch steering wheel. More play makes steering difficult and unsafe.

Q: What steering components should you check?

A: Check for missing nuts, bolts, or cotter keys; bent, loose, or broken parts (steering column, steering gear box, tie rods); power steering hoses, pumps, and fluid level; and any leaks.

Q: How do you check for steering mechanism looseness?

A: You must physically grab the steering mechanism components and test for play or looseness. Visual inspection alone isn't sufficient—you need to feel for excessive movement.

Brake Questions

Q: What brake drum defects should you look for?

A: Check for cracked drums, shoes or pads with oil/grease/brake fluid on them, and shoes that are worn dangerously thin, missing, or broken.

Q: How do you test parking brakes?

A: Set the parking brake, put the vehicle in low gear, and gently try to pull forward. The parking brake should hold the vehicle. If it doesn't hold, it's faulty and must be fixed.

Q: How do you test service brakes?

A: Drive at about 5 mph, then push the brake pedal firmly. Check if the vehicle pulls to one side (indicates brake trouble) and note any unusual pedal feel or delayed stopping action.

Q: What does it mean if the vehicle pulls to one side when braking?

A: Pulling to one side during braking indicates brake trouble—likely uneven braking between left and right sides. This needs immediate attention before driving.

Basic Control Questions

Q: How do you prevent rolling back when starting on a hill?

A: Use the parking brake. With manual transmission, partly engage the clutch before removing your foot from the brake. Apply enough engine power to prevent rollback before releasing the parking brake. On tractor-trailers, the trailer hand valve can also help.

Q: Why should you accelerate smoothly and gradually?

A: Rough acceleration causes mechanical damage to the drivetrain and can damage the coupling when pulling a trailer. In poor traction conditions, rough acceleration can cause wheel spin and loss of control.

Q: What should you do if drive wheels start to spin?

A: Take your foot off the accelerator immediately. Spinning wheels mean you're using too much power for the available traction. Gradually reapply power once wheels stop spinning.

Q: How should you hold the steering wheel?

A: Hold the steering wheel firmly with both hands on opposite sides. A firm grip prevents the wheel from being pulled from your hands if you hit a curb or pothole.

Backing Questions

Q: Why is backing always dangerous?

A: You cannot see everything behind your vehicle. There are blind spots that mirrors can't cover, and the size of commercial vehicles makes maneuvering difficult. Avoid backing whenever possible.

Q: Why should you back toward the driver's side?

A: You can see much better when backing toward the driver's side because you can look out the side window to watch the rear of your vehicle. Backing toward the right side is very dangerous due to limited visibility.

Q: What are the key rules for backing safely?

A: Start in the proper position, look at your path before backing (walk around if needed), use mirrors on both sides, back slowly (use lowest reverse gear), back toward the driver's side whenever possible, and use a helper when available.

Q: What should you agree on with a helper before backing?

A: Agree on hand signals that you both understand, especially a signal for "stop." The helper should stand near the back of your vehicle where you can see them.

Q: How slowly should you back?

A: Use the lowest reverse gear available. This gives you maximum control, allows easy correction of steering errors, and lets you stop quickly if needed.

Shifting Questions

Q: What is double clutching?

A: Double clutching is the method required for most heavy vehicle manual transmissions: push clutch to neutral, release clutch, let engine speed change to match the next gear, push clutch again, then shift. It allows gear changes without grinding.

Q: What are the two ways to know when to shift up?

A: Use engine speed (RPM)—shift when tachometer reaches the top of the operating range. Or use road speed (mph)—learn what speeds each gear handles and use the speedometer. You can also learn to use engine sounds.

Q: When should you downshift?

A: Downshift before starting down a hill (to control speed without heavy braking) and before entering a curve (to use power through the curve for stability).

Q: What gear should you use going down a hill?

A: Use a gear lower than the gear required to climb the same hill. This provides engine braking to control speed without overheating the brakes.

Q: What happens if you stay in neutral too long when shifting?

A: You may have difficulty getting into the next gear because engine and gear speeds won't match. If this happens, return to neutral, release clutch, adjust engine speed to match road speed, and try again. Don't force it.

Retarder Questions

Q: What is a retarder?

A: A retarder is a device that helps slow the vehicle, reducing brake use and wear. Types include exhaust, engine, hydraulic, and electric. When engaged, retarders apply braking power to drive wheels when you fully release the accelerator.

Q: When should you turn off retarders?

A: Turn retarders off when the road is wet, icy, or snow covered. When traction is poor, retarders can cause drive wheels to skid because they apply braking force only to drive wheels.

Q: Can retarders cause skidding?

A: Yes. Retarders apply braking to drive wheels only. On slippery surfaces, this can cause drive wheel skids. Always turn them off in poor traction conditions.

Cargo Inspection Questions

Q: How often must cargo securement be inspected?

A: Inspect cargo securement within the first 50 miles of a trip, then every 150 miles or 3 hours (whichever comes first) thereafter.

Q: What cargo items should you check?

A: Check that cargo is properly blocked, braced, tied, or chained. Verify header boards are adequate and secure, side boards/stakes are properly placed, tarps are secured (not blocking mirrors or lights), and doors are closed and latched.

Summary

Key numbers to remember for the CDL exam:

Ready to test your knowledge? Start practicing with our Vehicle Inspection questions.

See our Complete Guide to Vehicle Inspection and Basic Control for detailed information.