ASE T8 Preventive Maintenance Inspection (Medium/Heavy Truck) key terms

A structured walk-around and in-cab check performed before driving, covering lights, tires, brakes, fluids, coupling devices, and safety equipment to catch defects before the vehicle moves.

A written report the driver completes at the end of each shift listing defects found on the vehicle, which the carrier must review, repair, and certify before the vehicle returns to service.

The periodic full safety inspection of a commercial vehicle required at least once every 12 months, documented by a qualified inspector and supported by a sticker or report kept on file.

A published list of specific defects, such as a cracked brake drum or a loose wheel, that make a vehicle unsafe to operate until the defect is repaired and the vehicle passes re-inspection.

A safety procedure in which energy sources are shut off, isolated, and marked with a lock and tag so equipment cannot be started while a technician is servicing it.

Gear worn to reduce injury risk, such as safety glasses, gloves, hearing protection, and steel-toe boots, selected for the hazards of the task being performed.

A wedge placed against a tire to prevent the vehicle from rolling during service or inspection, used in pairs on the axle opposite the one being worked on.

A rigid support placed under the frame or axle to hold a raised vehicle securely after lifting, never relying on a hydraulic jack alone to support the load.

A braking system that uses compressed air to apply service brakes and spring pressure to apply parking brakes, with reservoirs, valves, and lines forming the circuit.

The maximum allowable pushrod travel for a given brake chamber size; exceeding it means the brake is out of adjustment and must be corrected before the vehicle is operated.

The lever and linkage that transmits force from the brake chamber pushrod to the brake shoe, and whose setting controls pushrod travel and brake adjustment.

A self-adjusting linkage that maintains brake chamber pushrod travel within limits during normal use, still requiring inspection because it can fail to adjust.

A device that removes moisture from compressed air before it reaches the reservoirs, protecting valves and lines from corrosion and freezing in cold weather.

A valve at the bottom of an air reservoir used to release accumulated water and oil, typically checked daily to keep the air system clean and functional.

A coupling on the end of a trailer air line that connects the tractor and trailer service and supply lines, sealed by a rubber gasket to prevent leaks.

The horseshoe-shaped coupling plate on the tractor that locks onto the trailer kingpin, transferring trailer load and towing force to the tractor frame.

The vertical pin mounted under the trailer that engages the fifth wheel jaws, securing the trailer to the tractor and allowing it to pivot.

The retractable legs under a trailer that support it when uncoupled, checked for bent legs, missing feet, and damaged cranks or gearing.

An exhaust aftertreatment component that traps soot from diesel exhaust and periodically burns it off during regeneration, requiring monitoring of soot load and ash buildup.

A urea-based solution injected into the exhaust stream to reduce nitrogen oxide emissions in selective catalytic reduction systems, checked for level and quality during service.

The high-temperature process that burns accumulated soot out of a diesel particulate filter, occurring passively during driving or actively when initiated by the engine controls.

The temperature at which engine coolant begins to freeze, tested with a refractometer or hydrometer to confirm the antifreeze mixture protects the engine in cold conditions.

Additives in coolant that prevent corrosion, cavitation, and scale in the cooling system, monitored by test strips or lab analysis and replenished as needed.

Laboratory testing of a fluid sample for wear metals, contaminants, and additive depletion, used to trend component condition and schedule maintenance intervals.

The noncombustible residue left when oil burns, an oil specification value that affects deposit formation and particulate filter life in modern diesel engines.

A small grease nipple installed on a joint or bearing that allows a grease gun to lubricate the component, checked during chassis lube service.

Scheduled greasing of steering, suspension, and driveline fittings to reduce wear, typically performed with a grease gun at every zerk fitting on the vehicle.

The measured groove depth remaining on a tire, checked with a gauge against legal minimums to determine whether the tire is safe and compliant.

The air pressure inside a tire, checked cold with a gauge and compared to the placard or load table, since incorrect pressure causes uneven wear and heat buildup.

A visual check of the tire sidewall for cuts, bulges, exposed cords, weathering, and mismatched sizes or load ratings that could indicate an unsafe tire.

The small amount of axial movement allowed in a wheel bearing assembly, checked to confirm bearings are correctly adjusted and not loose or over-tightened.

The specified tightening force applied to wheel fasteners in a star pattern, verified with a calibrated torque wrench to prevent wheel loss or stud damage.

Oil or grease escaping from a wheel hub seal, which can contaminate brake linings and indicates a worn seal or bearing that needs service.

The ball-and-socket joint connecting the steering linkage to the steering arm, checked for looseness, torn boots, and wear that affects steering control.

The amount of free play between the steering wheel and the road wheels, measured to detect worn steering components that make the vehicle wander or feel loose.

A stack of curved steel plates that supports axle load and absorbs road shock, inspected for cracked leaves, broken center bolts, and worn bushings or shackles.

A suspension system using inflatable rubber springs to carry load and adjust ride height, checked for leaks, chafing, and correct inflation.

Fluid escaping from a shock absorber body or seal, indicating worn internals that reduce damping and can cause tire cupping and poor handling.

A check that applies a heavy current draw to a battery while measuring voltage, confirming it can deliver cranking power under load.

A measurement of voltage lost across a circuit or connection while current flows, used to find excessive resistance in cables, grounds, and switches.

A check of charging system voltage and current at idle and under load, confirming the alternator keeps the battery charged and the regulator functions.

A vehicle network in which control modules share data over a serial bus instead of dedicated wires, requiring scan tool diagnostics for many electrical faults.

A stored code set by an electronic control module when it detects a fault, retrieved with a scan tool to guide troubleshooting and repair.

A check of the hood latch, safety catch, and hinges for proper engagement and lubrication, ensuring the hood cannot open unexpectedly while driving.

An examination of the bushings and bolts that attach the cab to the frame, looking for cracks, looseness, and deteriorated rubber that cause noise or poor alignment.

Setting the mirrors so the driver can see the required areas around the vehicle, including the blind spots on both sides and in front of the cab.