Vehicle Inspection and Basic Control - Complete Guide
Proper vehicle inspection and basic control skills form the foundation of safe commercial driving. Sections 2.1 through 2.3 of the CDL manual cover the 7-step inspection method, critical defects to identify, and essential vehicle control techniques including backing and shifting. Mastering these skills is crucial for both the CDL skills test and your daily safety as a professional driver.
Why Vehicle Inspection Matters
Safety is the most important reason for inspecting your vehicle—safety for yourself and other road users. A defect found during inspection could prevent a breakdown or crash. Federal and state laws require driver inspections, and inspectors can place unsafe vehicles "out of service" until repaired.
Important: You must pass a vehicle inspection test to obtain your CDL. You'll point to/touch items, name them, and explain what you're checking and why.
The 7-Step Inspection Method
Perform inspections the same way every time so you don't forget anything.
Step 1: Vehicle Overview
Approach the Vehicle:
- Look for damage or vehicle leaning to one side
- Check under vehicle for fresh oil, coolant, grease, or fuel leaks
- Check area for hazards (people, objects, low-hanging wires)
Review Last Inspection Report:
- Check for previous problems noted
- Verify repairs were made or certified unnecessary
Step 2: Check Engine Compartment
Set parking brakes and/or chock wheels first.
| Item | What to Check |
|---|---|
| Engine oil level | Adequate level on dipstick |
| Coolant level | Proper level; hose condition |
| Power steering fluid | Level and hose condition |
| Windshield washer fluid | Adequate level |
| Battery | Fluid level, connections, tie-downs |
| Belts | Tightness, excessive wear |
| Leaks | Fuel, coolant, oil, hydraulic fluid |
| Wiring | Cracked or worn insulation |
Step 3: Start Engine and Inspect Inside Cab
Start Engine:
- Parking brake on
- Transmission in neutral (or park)
- Listen for unusual noises
Check Gauges:
| Gauge | Normal Reading |
|---|---|
| Oil pressure | Comes up within seconds of starting |
| Air pressure | Builds 50-90 psi within 3 minutes |
| Ammeter/voltmeter | Normal range |
| Coolant temperature | Gradual rise to normal |
Check Controls:
- Steering wheel, clutch, accelerator
- Brake pedal, parking brake
- Transmission controls
- Lights, horn, wipers
Check ABS Light: Should come on then turn off. If it stays on, ABS is malfunctioning.
Check Emergency Equipment:
- Spare electrical fuses (unless circuit breakers)
- Three red reflective triangles
- Properly charged fire extinguisher
Step 4: Turn Off Engine and Check Lights
- Turn on headlights (low beams) and four-way flashers
- Check low beams and flashers working at front
- Check high beams work
- Turn on parking, clearance, side-marker, and ID lights
- Turn on right turn signal
- Begin walk-around
Step 5: Walk-Around Inspection
Left Front:
- Wheel/rim condition (missing, bent, broken parts)
- Tire condition (inflation, cuts, tread wear)
- Hub oil level, no leaks
- Suspension (springs, shocks, u-bolts)
- Brake drum/disc condition
Front:
- Axle condition
- Steering system (no loose, worn, bent parts)
- Windshield condition and wipers
- Lights and reflectors (amber at front)
Right Side:
- Same items as left front
- Fuel tank(s) secure, not leaking, caps on
- Exhaust system secure, not leaking
- Frame—no bends or cracks
Right Rear:
- Wheels, tires (properly matched, not rubbing)
- Suspension and brakes
- Lights/reflectors (red at rear)
- Cargo security
Rear:
- Lights (clearance, ID, tail, turn signals, license plate)
- Splash guards
- Cargo doors secured
Left Side:
- Same as right side
- Battery box secure, batteries secured, not leaking
Step 6: Check Signal Lights
- Turn off lights
- Apply brake (or have helper)
- Turn on left turn signal
- Check left front and rear turn signals
- Check both stop lights (red, yellow, or amber)
Step 7: Start Engine and Check Brakes
Test Hydraulic Brakes:
- Pump pedal 3 times
- Apply firm pressure, hold 5 seconds
- Pedal should NOT move (movement indicates leak)
Test Parking Brake:
- Set parking brake
- Put in low gear
- Gently pull forward—brake should hold
Test Service Brakes:
- Drive at 5 mph
- Push brake firmly
- Check for pulling to one side (indicates trouble)
- Check for unusual pedal feel or delayed stopping
Critical Defects to Identify
Tire Problems
| Defect | Requirement |
|---|---|
| Tread depth - front tires | Minimum 4/32 inch in every major groove |
| Tread depth - other tires | Minimum 2/32 inch |
| Fabric showing | Vehicle out of service |
| Cuts, bulges, tread separation | Dangerous—must repair |
| Dual tires touching | Must have space between |
| Mismatched sizes | Not permitted |
| Radial and bias-ply mixed | Not permitted together |
| Regrooved/recapped on bus front | Prohibited |
Suspension Defects
Look for these dangerous conditions:
- Spring hangers allowing axle movement from proper position
- Cracked or broken spring hangers
- Missing/broken leaf springs—if 1/4 or more missing = out of service
- Shifted leaves that might hit tire or other parts
- Leaking shock absorbers
- Damaged/leaking air suspension
- Cracked, damaged, or missing torque rods, u-bolts, or positioning parts
Warning: Broken suspension parts can be extremely dangerous because the suspension holds up the vehicle and keeps axles in place.
Steering Defects
- Missing nuts, bolts, cotter keys
- Bent, loose, or broken steering column, gear box, or tie rods
- Power steering leaks (check hoses, pumps, fluid)
- Steering wheel play exceeding 10 degrees (about 2 inches on 20-inch wheel)
Brake Defects
- Cracked drums
- Shoes/pads with oil, grease, or brake fluid
- Shoes worn thin, missing, or broken
- Brake hose wear from rubbing
Exhaust System Defects
- Loose, broken, or missing pipes, mufflers, stacks
- Missing mounting brackets, clamps, bolts
- Parts rubbing against fuel system, tires, or moving parts
- Leaking exhaust (can let poison fumes into cab)
Basic Vehicle Control
Accelerating
- Don't roll back when starting—use parking brake if needed
- Speed up smoothly and gradually to prevent mechanical damage
- In poor traction (rain/snow), accelerate very gradually
- If wheels spin, take foot off accelerator
Steering
- Hold wheel firmly with both hands on opposite sides
- Firm grip prevents wheel from pulling away when hitting curbs or potholes
Stopping
- Push brake pedal gradually
- Control pressure for smooth, safe stops
- With manual transmission, push clutch when engine near idle
Backing Safely
Backing is always dangerous—avoid whenever possible.
| Rule | Why It Matters |
|---|---|
| Start in proper position | Sets up safe backing path |
| Look at your path | Walk around, check clearance |
| Use mirrors on both sides | Check frequently during backing |
| Back slowly | Use lowest reverse gear for control |
| Back toward driver's side | You can see better out side window |
| Use a helper | They see your blind spots |
Critical: Back toward the driver's side whenever possible. Backing toward the right is very dangerous because you can't see as well. Go around the block if needed to position for driver-side backing.
Using a Helper:
- Helper stands where you can see them
- Agree on hand signals beforehand
- Agree on a "stop" signal
Shifting Gears
Double Clutching (Upshifting)
Most heavy vehicles require double clutching:
- Release accelerator, push clutch, shift to neutral
- Release clutch
- Let engine slow to rpm required for next gear
- Push clutch, shift to higher gear
- Release clutch, press accelerator
Knowing When to Shift Up
Two Methods:
| Method | How to Use |
|---|---|
| Engine RPM | Shift when tachometer reaches top of operating range |
| Road Speed | Learn what speeds each gear handles; use speedometer |
Downshifting
- Release accelerator, push clutch, shift to neutral
- Release clutch
- Press accelerator to increase engine rpm to match lower gear
- Push clutch, shift to lower gear
- Release clutch, press accelerator
When to Downshift
Before starting down a hill:
- Slow down and shift to gear you can control without heavy braking
- Usually need lower gear than required to climb the same hill
- Brakes can overheat and lose power if overused
Before entering a curve:
- Slow to safe speed
- Downshift before the curve
- Use power through curve for stability
Retarders
Retarders help slow the vehicle and reduce brake wear. Types: exhaust, engine, hydraulic, electric.
Warning: Turn retarders OFF when road is wet, icy, or snow covered. They can cause drive wheel skids when traction is poor.
Frequently Asked Questions
Q: What is the most important reason for vehicle inspection?
A: Safety—for yourself and other road users. Inspections find defects that could cause crashes or breakdowns. Federal and state laws require inspections, and unsafe vehicles will be placed out of service until repaired.
Q: What is the minimum tread depth for front tires?
A: Front tires require minimum 4/32 inch tread depth in every major groove. All other tires require minimum 2/32 inch. No fabric should show through tread or sidewall.
Q: What are the three types of emergency equipment 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: 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 does, there may be a leak—get it fixed before driving.
Q: Why should you back toward the driver's side?
A: You can see much better 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 because visibility is limited.
Q: What are the two ways to know when to shift gears?
A: Use engine speed (RPM)—shift when tachometer reaches top of 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 overusing brakes) and before entering a curve (to use power through the curve for stability). Downshift to a gear lower than needed to climb the same hill.
Q: What does excessive steering wheel play indicate?
A: Steering wheel play exceeding 10 degrees (about 2 inches of movement at the rim of a 20-inch wheel) indicates steering problems that make the vehicle hard to steer safely. This is a serious defect.
Q: What suspension defect puts a vehicle out of service?
A: If one-fourth or more of the leaves in a leaf spring are missing, the vehicle is out of service. Any broken spring hangers, cracked parts, or defects allowing axle movement from proper position are also dangerous.
Q: When should you turn off retarders?
A: Turn retarders off whenever the road is wet, icy, or snow covered. When drive wheels have poor traction, retarders can cause them to skid.
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 (typically 120-140 psi). Know your vehicle's specific requirements.
Q: What should the ABS indicator light do?
A: The ABS light on the dash should come on when you start the engine, then turn off. If it stays on, the ABS is not working properly. For trailers, check the yellow light on the left rear.
Next Steps
Understanding vehicle inspection and basic control is essential for both the CDL skills test and safe daily operation:
- Practice the 7-step inspection until it becomes automatic
- Memorize the minimum tread depths and critical defect indicators
- Practice backing toward the driver's side
- Learn the RPM ranges for your specific vehicle
Ready to test your knowledge? Start practicing with our Vehicle Inspection questions.
See our guides on Air Brakes (Section 5) and Combination Vehicles (Section 6) for additional inspection requirements.