ASE P1 Medium-Heavy Truck Parts Specialist cheat sheet

Reorder point = (average daily demand × lead time in days) + safety stock.

Economic order quantity (EOQ) = √(2DS / H), where D = annual demand, S = order cost, H = holding cost per unit per year.

Inventory turnover ratio = cost of goods sold ÷ average inventory value; higher ratios indicate faster-moving stock.

ABC classification: A items are high-value/low-count (top ~80% of value), B moderate, C low-value/high-count.

Perpetual inventory system continuously updates stock levels with each transaction; periodic system counts at set intervals.

Cycle counting counts a subset of inventory on a rotating schedule to verify accuracy without full physical inventory.

Fill rate = (units shipped immediately ÷ units ordered) × 100%; measures ability to meet demand from stock.

Obsolescence reserve is an allowance for inventory that is no longer sellable due to age or model changes.

VIN positions 1-3 = World Manufacturer Identifier (WMI); positions 4-8 = vehicle attributes; position 9 = check digit; position 10 = model year; position 11 = plant; positions 12-17 = sequential serial number.

VIN model year codes: 2010=A, 2011=B, 2012=C, 2013=D, 2014=E, 2015=F, 2016=G, 2017=H, 2018=J, 2019=K, 2020=L, 2021=M, 2022=N, 2023=P, 2024=R, 2025=S.

Interchange numbers (e.g., Hollander, OEM cross-reference) indicate parts that are functionally equivalent but may have different casting numbers.

Supersession occurs when a manufacturer replaces a part number with a new number; the new number is backward-compatible.

OEM part numbers often embed vehicle line, component group, and engineering revision codes; do not assume sequential logic.

Aftermarket cataloging uses ACES (vehicle application) and PIES (product information) standards for electronic data exchange.

Casting numbers are found on the part itself and may differ from the catalog part number; use both for positive identification.

Right-hand and left-hand parts are not interchangeable; verify orientation using the catalog illustration or part description.

Diesel compression ignition: air is compressed to high pressure/temperature, then fuel is injected and ignites spontaneously; compression ratios typically 16:1 to 22:1.

Four-stroke cycle order: intake, compression, power (expansion), exhaust; crankshaft completes two revolutions per cycle.

Common rail fuel systems use a high-pressure accumulator (rail) and electronically controlled injectors; rail pressure can exceed 30,000 psi (2,000 bar).

Turbocharger boost pressure is measured in psi or bar; wastegate or VGT (variable geometry turbo) controls boost to prevent overboost.

EGR (exhaust gas recirculation) reduces NOx by recirculating exhaust into the intake; cooler fouling can cause poor performance.

Diesel particulate filter (DPF) traps soot; regeneration occurs passively (heat) or actively (post-injection) to oxidize accumulated soot.

Engine displacement = (π/4) × bore² × stroke × number of cylinders; units must be consistent.

Valve lash (clearance) is measured with a feeler gauge and adjusted to manufacturer specification; incorrect lash affects timing and noise.

Manual transmission gear ratio = number of teeth on driven gear ÷ number of teeth on drive gear.

Overall drive ratio = transmission gear ratio × axle ratio; used to calculate engine RPM at a given road speed.

Road speed (mph) = (engine RPM × tire circumference in inches) ÷ (overall ratio × 1056).

Automatic transmission fluid (ATF) must meet the OEM specification (e.g., Dexron, Mercon, TES-295); wrong fluid can cause shift problems.

Differential gear ratio is the number of ring gear teeth divided by the number of pinion gear teeth.

Limited-slip differentials use clutch packs or gear-type mechanisms to limit wheel spin; require specific lubricant with friction modifier.

Driveshaft phasing: universal joints must be aligned so that yoke ears are in the same plane to minimize vibration.

Clutch free play is the distance the pedal moves before the throwout bearing contacts the pressure plate; incorrect free play causes slippage or drag.

Hydraulic brake system: force applied at pedal is multiplied by pedal ratio and by the ratio of master cylinder bore area to caliper/wheel cylinder bore area.

Brake fluid must meet DOT 3, DOT 4, or DOT 5.1 specifications; DOT 5 is silicone-based and not compatible with glycol-based fluids.

Air brake systems use a compressor, reservoirs, governor, and valves; system pressure is typically 100–120 psi with a governor cut-out around 120–130 psi.

Slack adjuster adjustment ensures proper pushrod stroke; excessive stroke reduces braking force and indicates worn foundation brakes.

Automatic slack adjusters should not be manually adjusted unless the vehicle manufacturer permits; they self-adjust during brake applications.

Brake drum diameter and brake shoe thickness must be measured against OEM specifications to determine wear and replacement.

Anti-lock brake system (ABS) wheel speed sensors generate a signal; a damaged tone ring or sensor air gap can cause fault codes.

Parking brake (spring brake) uses a spring to apply brakes when air pressure is released; loss of air pressure causes parking brake application.

Ackermann steering geometry: inner wheel turns at a sharper angle than outer wheel to reduce tire scrub.

Toe-in is the difference in distance between the front and rear of the front tires; measured in inches or degrees.

Caster is the forward or rearward tilt of the steering axis; positive caster improves straight-line stability.

Camber is the inward or outward tilt of the wheel; negative camber tilts the top inward.

Kingpin inclination (KPI) is the angle between the kingpin axis and vertical, viewed from the front.

Wheel-end components include hub, bearings, seals, spindle, and wheel studs; bearing preload is critical for longevity.

Leaf spring capacity is rated by load; adding leaves increases capacity but may affect ride height and alignment.

Air suspension uses air springs, height control valves, and a compressor; ride height is maintained by adjusting air pressure.

Ohm's law: V = I × R; power P = V × I = I²R = V²/R.

Series circuit: total resistance = sum of resistances; current is the same through all components; voltage divides.

Parallel circuit: total resistance is less than the smallest individual resistance; voltage is the same across all branches; current divides.

Battery capacity is rated in cold cranking amps (CCA) and reserve capacity (RC); CCA indicates starting ability at cold temperatures.

Alternator output is rated in amperes; charging system voltage should be approximately 13.5–14.5 volts with engine running.

Starter circuit includes battery, cables, solenoid, and starter motor; voltage drop across cables should be less than 0.5 volts total.

SAE J1939 is the standard for heavy-duty vehicle network communication; uses CAN bus at 250 kbps or 500 kbps.

Fuses protect circuits by melting when current exceeds rating; circuit breakers reset automatically or manually.

Coolant types: ethylene glycol (EG) and propylene glycol (PG); EG has better heat transfer, PG is less toxic.

Coolant mixture is typically 50/50 antifreeze and water; provides freeze protection to about -34°F (-37°C) and boilover protection.

Diesel engine coolant requires supplemental coolant additives (SCAs) or extended-life organic acid technology (OAT) to prevent liner cavitation.

Oil viscosity grades (e.g., 15W-40) indicate cold-temperature (W) and high-temperature performance; follow OEM recommendation.

API oil service categories: CJ-4, CK-4 for diesel engines; FA-4 for improved fuel economy.

Oil filters should be changed at each oil change; bypass filtration can extend oil life but does not replace full-flow filtration.

Radiator pressure cap raises coolant boiling point; typically 7–15 psi for heavy-duty applications.

Thermostat regulates coolant flow to maintain operating temperature; opening temperature is stamped on the thermostat.

Air conditioning refrigerant R-134a is being phased out in favor of R-1234yf in newer vehicles; refrigerants are not interchangeable.

A/C system pressures: low side typically 25–45 psi, high side 150–250 psi depending on ambient temperature.

Refrigerant oil (PAG or POE) must be compatible with the refrigerant and added when replacing components.

Heater core uses engine coolant to warm air; a leaking heater core can cause coolant loss and fogging on the windshield.

Blend door actuator controls air temperature by mixing hot and cold air; failure causes temperature control issues.

Cab mounts and bushings isolate vibration; worn mounts cause noise and misalignment of cab components.

Chassis components include frame, crossmembers, and brackets; inspect for cracks and loose fasteners.

HVAC blower motor resistor controls fan speed; a failed resistor can cause only certain speeds to work or no fan operation.

Warranty return requires proof of purchase, part number, and reason for return; follow manufacturer's warranty claim process.

Core charges are refundable deposits on rebuildable parts; core must be returned in acceptable condition to receive credit.

Return authorization (RA) number is required before returning parts; unauthorized returns may be refused.

Special order parts are often non-returnable; confirm before ordering to avoid restocking fees.

Restocking fees typically range from 10% to 25% for returned parts that are not defective.

Warranty period is defined by the manufacturer; labor may or may not be covered depending on policy.

Customer service: listen actively, verify VIN and part number, and confirm application before finalizing sale.

Upselling should be based on genuine need (e.g., related wear items) and not on pushing unnecessary products.