Vehicle Systems, Inspection, and Maintenance
This domain tests vehicle systems and maintenance: brakes, tires, coupling, lights, and inspection reports. The exam expects you to know when a vehicle is out of service.
Brakes
Know the air system components and slack adjuster limits. Check pushrod travel against the limit; excessive travel means the brake is out of adjustment and the vehicle should not be driven. Test ABS warning lights.
Tires and wheels
Minimum tread depth is 4/32 inch on front steer tires and 2/32 inch on other tires. Check inflation, cuts, bulges, and loose lug nuts. Rust streaks can indicate loose nuts.
Coupling and lights
After coupling, check that the fifth wheel jaws are locked around the kingpin and the safety latch is closed; do a tug test. Check all lights and reflectors.
Inspections
Commercial vehicles need a periodic inspection every 12 months. Drivers complete a daily vehicle inspection report (DVIR) and note defects; a vehicle with a safety defect must not be operated until repaired.
Worked example
A slack adjuster pushrod moves beyond the adjustment limit. Reasoning: the brake may not apply fully, so the vehicle is out of service. The driver notes the defect on the DVIR and does not drive until it is repaired.
Traps that cost marks
Assuming 2/32 inch is legal for steer tires; skipping the tug test; signing a DVIR without checking the vehicle.