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ASE Certified School Bus Diesel Engines (S2) — Requirements & Free Practice

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ASE Certified School Bus Diesel Engines (S2)

Licensing authority: National Institute for Automotive Service Excellence

Initial by examination
ASE School Bus Diesel Engines (S2)
Ase Review
ASE may verify employment, deny certification for false or misleading information, and evaluate substitutions or other experience for appropriate credit.
Certification
Pass the initial S2 Diesel Engines examination and obtain ASE approval of the relevant work-experience documentation. This is the individual S2 certification, not Master School Bus Technician status.
Experience
Two years full-time (or part-time equivalent) of hands-on Repair Technician experience maintaining, servicing, and/or repairing light-duty or heavy-duty motor vehicles. An applicant may test before meeting experience requirements but receives only a score report until the requirement is fulfilled.
Formal Education Alternatives
["Complete an ASE-accredited Auto, M/H Truck or Collision-Refinish program, including MLR, AST, MAST and other current or grandfathered standards: one year credit toward the two-year requirement.","Complete an ASE-accredited OEM-sponsored co-op program, including its hands-on co-op portion: two years credit toward the two-year requirement.","Pass three or more different ASE Entry-Level Certification Program tests: one year credit toward the two-year requirement; these are not professional certification examinations and are only an optional experience substitution.","Other training: two months full-time training (or 200 program hours) equals one month credit, up to one year toward the two-year requirement."]
Formal Education Limits
The four formal education substitutes cannot be combined. Programs in the first two categories must be completed in full and accredited at completion. Supply program completion certificates, Entry-Level test certificates, or an official transcript showing training hours/weeks and completion date, as applicable. Remaining required credit can be fulfilled with hands-on experience.
Language And Validity
Only the English initial S2 examination is submitted. The glossary does not create another examination version. No official start or end date for this current S2 specification or this route is published in the consulted current materials; dates remain null. The current S-series page links the 2026 guide and agrees on S2 identity and assessment. Individual credentials require renewal after five years; renewal production is outside this task.
Other Exams
The published S2 initial certification route does not adopt L3 or L4; the ASE FAQ identifies advanced-level prerequisites as applying to those advanced-level tests. No advanced-level, student, recertification, T-series or Master-status exam is added as a required S2 leaf.
Other Experience Alternatives
["Current I-CAR Platinum status satisfies the Repair Technician two-year requirement corresponding to the held role; provide the current certificate.","Military experience can qualify; provide DD Form 2586 (VMET), DD Form 214, or JST for ASE evaluation.","A current valid Canadian provincial automotive trade certificate is acceptable evidence for the one- and two-year Repair Technician requirements; provide a copy.","Licensed repair-business owner/operators may receive self-employment credit for diagnosis and repair work in their shop, with service details, duration and current business license; home-garage repairs are not accepted.","Full-time instructor (not teaching assistant) experience of four academic years or part-time equivalent in a high-school or post-secondary Auto, M/H Truck or Collision-Refinish program, plus at least 20 hours of technical update training in the preceding 12 months, satisfies the corresponding two-year requirement. Provide a principal/dean letter and training records. This alternative cannot be combined with traditional hands-on experience or formal education substitutions."]
Registration
Create or use a personal myASE account, purchase the S2 initial certification test, and schedule and complete an in-person Prometric test-center appointment within 90 days of purchase. Testing is available year-round; current registration windows are published by ASE. Initial S2 is not an on-demand unproctored online test and is not eligible under the recertifier/G1 remote-testing exception.

ASE School Bus Diesel Engines (S2)

Provider
Prometric test centers
Format
Computer-based multiple-choice initial certification examination in English; appointment at a test center required.
Exam questions
Total questions: 65; Scored questions: 55; Unscored questions: 10; The total includes the scored and unscored questions.
Time limit
90 minutes
Examination outline
  • General Engine Diagnosis (27%)
    • Complaint verification, road test and maintenance history
    • Engine identification, EPA certification and service information
    • Engine assembly and compartment leak inspection
    • Wiring harness, connectors, seals and locks
    • Engine noises and vibrations
    • Exhaust odor, smoke, volume and opacity
    • Fuel supply, return, contamination, quality and consumption
    • Air intake restriction and leakage
    • Intake manifold and system pressure
    • Exhaust back pressure, temperature, soot and ash
    • Open and closed crankcase pressure tests
    • Cranking, starting and continued running problems
    • Engine running, power, acceleration and shutdown problems
    • Cooling system condition and operation
    • Lubrication diagnosis, oil analysis, oil and filter service
    • Diagnostic tools, software, DTCs, data and repair verification
    • Diesel exhaust fluid system diagnosis
    • Physical damage, missing components and tampering
  • In-Chassis Engine Inspection and Repair (11%)
    • Cylinder head assembly removal and installation
    • Threaded holes, studs and bolts
    • Cylinder head measurements, warpage, damage and passages
    • Injector bores, sleeves and seals
    • Valves, springs, guides and related components
    • Pushrods, rocker components, wiring and brackets
    • Camshaft, bearings, followers, endplay and lift
    • Engine gear train, timing and position components
    • Valve clearance and injector settings
    • Pans, covers, accessories, mounts, gaskets and seals
    • Engine block assembly inspection and service
    • Liner protrusion and counterbore depth
    • Crankshaft vibration damper
    • Flywheel, flexplate, ring gear and housing
    • Cylinders, liners, rods, wrist pins, pistons and rings
    • Crankshaft, journals, passages, nozzles and clearances
  • Lubrication and Cooling Systems Diagnosis and Repair (13%)
    • Oil pressure, temperature and warning instrumentation
    • Oil pump and drive service
    • Oil regulation, bypass valves and filters
    • Oil cooler, thermostat, lines and hoses
    • Turbocharger lubrication and cooling
    • Pulleys, tensioners and drive belts
    • Coolant temperature, level and warning instrumentation
    • Coolant thermostats, bypasses, seals and restrictors
    • Coolant flushing, refilling, bleeding and recycling
    • Coolant conditioner, filter, valves and housing
    • Coolant pumps, housings, hoses and drives
    • Cooling system pressure tests, caps and tanks
    • Cooling airflow, fan and controls
    • Radiator coverings, shutters and winter fronts
    • Engine block heater and auxiliary coolant heating
  • Air Induction and Exhaust Systems Diagnosis and Repair (16%)
    • Air induction piping, cleaner, restriction and drain
    • Turbochargers, controls, wastegates and calibration
    • Intake manifold, gaskets, sensors and connectors
    • Charge air cooler, piping and connections
    • Exhaust manifold, piping, muffler and mounting
    • Intake heaters, glow plugs and controls
    • Exhaust aftertreatment, DEF, SCR, DPF and regeneration
    • Exhaust gas recirculation components and circuits
  • Fuel System Diagnosis and Repair (27%)
    • Fuel tanks, protection, valves, lines and fittings
    • Fuel transfer, separation, filtration, heating and cooling
    • Fuel leaks, aeration, contamination, priming and bleeding
    • Low-pressure fuel regulation
    • High-pressure injection lines, tubes and seals
    • High-pressure common rail fuel systems and controls
    • Hydraulic electronic unit injector systems and controls
    • Electronic unit injector systems and controls
    • Manual, electronic and air throttle controls
    • Engine protection and shutdown or derate systems
    • Fuel-system electrical connections and harnesses
    • Software, injector calibration, parameters and relearning
    • Electronic engine control components and circuits
    • Electrical measurement and test equipment
  • Starting System Diagnosis and Repair (6%)
    • Battery identification, state of charge, load and capacity
    • Battery charging
    • Jump starting and auxiliary power
    • Battery, cable and terminal service and voltage drop
    • Starters, relays, switches, interlocks and solenoids
    • Starter current draw
    • Starter circuit voltage drop
Examination sources