What lighting is covered?

Part 393 specifies the required color, position, and types of lamps and reflectors for commercial motor vehicles. All lamps and reflectors for commercial motor vehicles manufactured after March 7, 1989 must meet the requirements of Federal Motor Vehicle Safety Standard (FMVSS) No. 108 (49 CFR 571.108) in effect on the date of manufacture. Certain trailers manufactured on or after December 1, 1993, must have retroreflective sheeting or additional reflex reflectors to make them more visible to other motorists at nighttime and under other conditions of reduced visibility. Trailers manufactured before December 1, 1993 must be retrofitted with retroflective sheeting or additional reflectors by June 1, 2001.

Lamps and reflectors on commercial motor vehicles manufactured on or prior to March 7, 1989 must meet either the requirements of Part 393 or of FMVSS No. 108 that were in effect on the date of manufacture.

Must be operable

All required lamps must light on request at an inspection and must light when required during regular operation of the vehicle.

Lamp mounting

All lamps must be permanently and securely mounted on a permanent part of the vehicle. The exceptions are temporary lamps, such as those used in a driveaway-towaway operation or mounted on projecting loads. Temporary lamps must be securely attached.

Stop lamps

All stop lamps on a commercial motor vehicle must activate when the service brakes are applied.

A service brake system that meets the requirements of 49 CFR 393.52, which specifies braking and holding performance.

• A parking brake system that meets the requirements of 49 CFR 393.41, which specifies parking brake activation and the method for holding the brakes in the applied position.

Trucks and truck tractors with three or more axles, manufactured before July 25, 1980, are not required to have steering axle brakes.

• Vehicles being towed in a driveaway-towaway operation. (However, the towed vehicle must have brakes in operation if the brakes on the towing vehicle are not capable of stopping the combination vehicle under the conditions covered by Section 393.52.)
• Any full trailer, semitrailer, or pole trailer having a gross weight of 3,000 pounds or less, provided the trailer weight does not exceed 40 percent of weight of the towing vehicle.

Every truck or truck tractor equipped with air brakes, when used to tow other vehicles equipped with air brakes, must be capable of activating (manually and automatically) the emergency features of the trailer brakes. The brakes must apply automatically when the towing vehicle air supply pressure is between 20 and 45 psi. The manual control must be operable by the driver from the driver's seat, with seat belt in use.

• Every trailer is required to be equipped with brakes that apply automatically if the trailer breaks away from the towing vehicle*. The brakes must remain in the applied position for at least 15 minutes.

* These requirements do not apply to vehicles in driveaway-towaway operations.

Design and construction of brake tubing and hose must ensure proper, adequate, and continued functioning.

• Installation must ensure proper functioning of the hose.
• Length and flexibility must accommodate all normal motions of the parts to which the hose is attached.
• Protection against mechanical damage must include protection against chafing, kinking, and mechanical damage.
• Protection from high temperature must include protection from or location away from exhaust pipes and other sources of high temperatures.

Truck-tractors manufactured on or after March 1, 1997;

• Air-braked single-unit trucks, buses, and trailers (including converter dollies) manufactured on or after March 1, 1998; and
• Hydraulic-braked trucks and buses manufactured on or after March 1999.

No part of the system extends beyond the widest part of the vehicle.

• No part of a fuel tank is forward of the front axle or a power unit.
• Fuel lines do not extend between a towed vehicle and the towing unit while the combination is in motion.
• No part of the fuel system of a bus manufactured on or after January 1, 1973, is located within or above the passenger compartment.

Body ply or belt material exposed through the tread or sidewall

• Tread or sidewall separation
• Audible leak (or flat)
• A cut exposing the ply or belt material
• A tread groove pattern depth of less than 4/32 of an inch (front tires) or 2/32 of an inch (other tires)
• Regrooved tires on front wheels of trucks or truck tractors which have a load carrying capacity equal to or greater than 8.25-20 8-ply rating tires
• Regrooved, recapped, or retreaded tires on the front wheels of buses are prohibited.

The exhaust system and discharge must be located where it is not likely to burn or damage the electrical wiring, the fuel supply, nor any combustible part of the vehicle.

• The discharge from the exhaust system must not be located immediately below the fuel tank or the fuel tank filler pipe.
• The exhaust system may not be temporarily repaired with patch or wrap material.
• The exhaust pipe and mufflers must be securely fastened to the vehicle.
• The exhaust system may not leak or discharge at any point forward of or directly below the driver or sleeper compartment.

For trucks and truck tractors, the exhaust system must discharge at a location to the rear of the cab, or above and near the rear of the cab.

For a bus powered by a gasoline engine, the exhaust pipe must discharge at a point no farther forward than six inches forward of the rearmost part of the bus.

For a bus powered by diesel or other fuel (not gasoline), the exhaust pipe must discharge either:

At a point no farther forward than 15 inches forward of the rearmost part of the bus, or

• To the rear of all doors or windows designed to be open (not including emergency exits).

Fire extinguisher (not required for driveaway-towaway operations)

• Spare fuses
• Warning devices for stopped vehicles.

One extinguisher with a UL rating of 5 B:C or more, or

• Two extinguishers each with a UL rating of 4 B:C or more.
• One extinguisher with a UL rating of 10 B:C, if the vehicle is transporting placardable quantities of hazardous material.

Frames, Cab and Body Components, Wheels, Steering, and Suspension Systems

Axles must be in proper alignment, and no positioning part can be cracked, broken, loose, or missing.

• Adjustable axles must have locking pins in place.
• Leaf springs must not be cracked, broken, missing, or shifted out of position.
• Coil springs must not be cracked or broken.
• Torsion bars must not be cracked or broken.
• Air suspensions must support the vehicle in a level position, and must not leak.

Steering wheel must be properly secured and no cracked or missing spokes.

• Steering wheel lash must meet the requirements of Section 393.209.
• Steering column must be securely fastened.
• Steering system must not have worn or welded universal joints, loose steering gear box, missing bolts, or a loose pitman arm on the steering gear output shaft.
• Power steering unit must not have loose or broken parts, frayed, cracked, or slipping belts; leaks; or insufficient fluid in reservoir.