ASE P1 Medium-Heavy Truck Parts Specialist key terms

An inventory method that continuously updates on-hand quantities and dollar values as parts are received, sold, or returned, so stock records stay current rather than being corrected only at physical counts.

The minimum quantity that triggers a reorder and the maximum quantity to keep on hand, set to balance stockout risk against carrying cost for each part number.

The on-hand quantity at which a new purchase order should be placed, calculated from average daily demand multiplied by lead time plus a safety margin.

A program of counting a small, rotating subset of parts on a scheduled basis instead of shutting down for one full physical inventory, used to find and correct record errors.

Stock that no longer sells because the vehicle population, part supersession, or customer demand has changed, tying up capital and shelf space until it is returned, discounted, or scrapped.

The 17-character vehicle identification number assigned by the manufacturer; decoding it confirms year, engine, brake system, and other attributes needed to select the correct replacement part.

The process of matching a part number to a specific vehicle by year, make, model, engine, and options, using catalog guides or electronic lookup rather than appearance alone.

The manufacturer's or supplier's reference that lists part numbers, illustrations, descriptions, quantities, and vehicle applications for a given system or assembly.

A manufacturer's replacement of one part number with another that fits and functions the same or better, requiring the counterperson to sell the current number and note the change.

A cross-reference that shows which part numbers from different manufacturers or brands will substitute for each other, allowing alternatives when the original supplier's part is unavailable.

The original equipment manufacturer's unique identifier for a component, used to order exact replacement parts and to cross-reference aftermarket equivalents.

A component produced by a company other than the original vehicle manufacturer, often offered at lower cost or in upgraded designs, and identified through interchange rather than OEM numbering.

A refundable deposit added to the price of a rebuilt or remanufactured part, returned to the customer when the old unit is brought back for rebuilding.

A used assembly that has been completely disassembled, inspected, machined or replaced as needed, and rebuilt to original specifications, usually carrying its own warranty.

An exhaust aftertreatment device that traps soot from diesel exhaust and burns it off during regeneration; related sensors and filters are stocked as service parts.

A heat exchanger that lowers the temperature of exhaust gas recirculated into the intake to reduce nitrogen oxide formation; a common replacement item on heavy-duty diesel engines.

An exhaust-driven compressor that forces extra air into the engine cylinders to increase power; sold as an assembly or as a cartridge, with mounting gaskets and hardware often required.

A radiator-like heat exchanger that cools compressed intake air after the turbocharger, increasing air density; hoses, clamps, and the cooler itself are stocked cooling-system parts.

A precision component that meters and atomizes fuel into the combustion chamber; on diesel engines it is often coded to the cylinder and may require programming after replacement.

The sleeve pressed into the cylinder head that seals the injector from coolant and combustion gases; replacement cups and seals are stocked with injector service parts.

A small air or hydraulic device that slows the transmission input shaft so gears can be engaged without grinding in a nonsynchronized heavy-duty manual transmission.

The bearing that pushes against the clutch diaphragm or fingers when the pedal is depressed, disengaging the clutch; sold with the clutch kit and often with the fork.

A small bearing in the end of the crankshaft that supports the front of the transmission input shaft, reducing vibration and misalignment between engine and transmission.

The working angle between the transmission output, driveshaft sections, and axle pinion; incorrect angles cause vibration and premature universal joint and carrier bearing failure.

A cross-and-bearing joint that allows the driveshaft to transmit torque through changing angles; sold as a kit with caps, snap rings, and sometimes a center ball.

A support bearing with a rubber cushion that holds the center of a two-piece driveshaft, absorbing vibration and maintaining alignment; a common wear item on long-wheelbase trucks.

A device on the air brake system that removes moisture and oil from compressed air before it reaches the reservoirs, protecting valves and preventing freeze-ups.

A valve that speeds application and release of the rear service brakes by sending reservoir air directly to the brake chambers when signaled by the foot valve.

The linkage that converts brake chamber pushrod travel into rotation of the brake camshaft; automatic versions maintain adjustment and are sold with clevis pins and bushings.

The air cylinder that converts air pressure into mechanical force on the foundation brakes; service and spring (parking) chambers are matched to axle and brake size.

The hardened pin that connects the steering knuckle to the front axle beam and allows the wheels to pivot; sold with bushings, shims, and seals in a repair kit.

The ball-and-socket joint at the end of the steering linkage that connects to the steering arm; wear causes tire scrub and play in the steering wheel.

The link that transfers steering motion from the steering gear arm to the steering knuckle or tie rod assembly on a commercial truck front end.

The lip seal that retains oil or grease in the wheel hub and keeps contaminants out; matched to hub and spindle dimensions and often replaced with bearings.

The tapered roller or unitized bearing that supports the hub on the spindle; sold individually or in kits with races, seals, and adjusting nuts.

The belt-driven generator that charges the batteries and powers electrical loads while the engine runs; rated by amperage and matched to the vehicle's electrical demand.

The electric motor that cranks the engine using battery power; specified by voltage, rotation, and mounting pattern, and often sold with a solenoid.

The number of minutes a fully charged battery at 80 degrees Fahrenheit can supply 25 amps before falling below 10.5 volts, indicating how long electrical loads can run if charging fails.

An additive package, often sold as a filter with a built-in charge, that maintains corrosion inhibitors and pH in heavy-duty coolant between drains.

A canister or cartridge that removes contaminants from engine oil; specified by thread size, bypass pressure, and micron rating, with full-flow and bypass types sometimes both used.

A filter assembly that removes water and particulate from diesel fuel before it reaches the injection system; drain intervals and element numbers must match the application.

The small electric motor that moves the HVAC blend door to control air temperature in the cab; a common replacement part for no-heat or no-cool complaints.

A canister on the liquid line that stores refrigerant, holds desiccant to absorb moisture, and filters debris; replaced whenever the system is opened for major repairs.

A formal request to a supplier or manufacturer for credit or replacement of a failed part under warranty, requiring proof of purchase, installation details, and often the returned part.

A percentage deducted from a refund when a customer returns a nondefective special-order or electrical part, covering the cost of processing and reshelving the item.