DOT Commercial Vehicle Inspection Standards 2 — Questions and Answers
Question 1: Under FMCSA regulations, what is the minimum tread depth required for front steering axle tires on a commercial vehicle?
- 2/32 inch
- 4/32 inch (Correct answer)
- 6/32 inch
- 8/32 inch
Correct answer: 4/32 inch
Front steering axle tires must have a minimum tread depth of 4/32 inch, while other tires require at least 2/32 inch.
Question 2: During a brake inspection, a CMV is found to have 25% of its service brakes out of adjustment. What action should the inspector take?
- Issue a warning and allow the vehicle to proceed
- Place the vehicle out of service immediately (Correct answer)
- Allow travel to nearest repair facility only
- Require repair within 24 hours
Correct answer: Place the vehicle out of service immediately
A vehicle is placed out of service if 20% or more of its service brakes are defective or out of adjustment.
Question 3: Which federal regulation establishes the out-of-service criteria for commercial motor vehicles during roadside inspections?
- 49 CFR Part 390
- 49 CFR Part 393 (Correct answer)
- 49 CFR Part 395
- 49 CFR Part 396
Correct answer: 49 CFR Part 393
49 CFR Part 393 covers parts and accessories necessary for safe operation and forms the basis for OOS criteria.
Question 4: What is the maximum allowable slack adjuster travel (pushrod stroke) for a Type 30 brake chamber at a 90 psi application?
- 1.5 inches
- 2.0 inches (Correct answer)
- 2.5 inches
- 3.0 inches
Correct answer: 2.0 inches
For a Type 30 brake chamber, the maximum pushrod stroke at 90 psi is 2.0 inches before the brake is considered out of adjustment.
Question 5: A commercial vehicle's frame has a crack running perpendicular to the vehicle's length. This condition is considered:
- Acceptable if the crack is less than 6 inches long
- An out-of-service defect (Correct answer)
- A minor defect requiring repair within 30 days
- Acceptable if the vehicle is not fully loaded
Correct answer: An out-of-service defect
Any crack in the vehicle frame is an out-of-service condition regardless of length or load status.
Question 6: Under 49 CFR Part 393, which lighting device is NOT required to be operational on a CMV during daylight hours?
- Brake lights
- Turn signals
- Headlights (Correct answer)
- License plate lamp
Correct answer: Headlights
Headlights are not required to be operational during daylight hours, though all other required lighting must function at all times.
Question 7: When inspecting a CMV's coupling devices, which condition would result in an out-of-service order for the fifth wheel?
- Slight surface rust on the fifth wheel plate
- Missing or non-functioning locking mechanism (Correct answer)
- Grease buildup on the kingpin plate
- Wear patterns on the mounting bracket
Correct answer: Missing or non-functioning locking mechanism
A missing or non-functioning locking mechanism on a fifth wheel is an out-of-service defect because it prevents secure coupling.
DOT Commercial Vehicle Inspection Standards 2
Under FMCSA regulations, what is the minimum tread depth required for front steering axle tires on a commercial vehicle?