Answer 10 free questions

ASE Transit Bus: 10 free questions

Tap an answer to see if you're right and why, or switch to Timed and get scored at the end. Each answer is also under its question.

1. ASE H1 Transit Bus — CNG Engines

   On a transit bus CNG fuel system, the cylinders store fuel at a full service (settled) pressure of about:

   A250 psi B900 psi C3,600 psi D10,000 psi
   Show answer

   Answer: C. 3,600 psi

   The industry-standard CNG service pressure is 3,600 psi (about 24.8 MPa) measured as a settled pressure at 70 F; older systems used 3,000 psi.

2. ASE H2 Transit Bus — Diesel Engines

   Diesel exhaust fluid (DEF) used in an SCR aftertreatment system is a solution of:

   A32.5% urea and 67.5% deionized water B50% urea and 50% distilled water CPure anhydrous ammonia D32.5% ammonia and 67.5% diesel fuel
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   Answer: A. 32.5% urea and 67.5% deionized water

   DEF meeting ISO 22241 is 32.5% high-purity urea and 67.5% deionized water; heat in the exhaust decomposes the urea to ammonia, which then reacts with NOx over the SCR catalyst.

3. ASE H3 Transit Bus — Drive Train

   The three primary members of a heavy-duty automatic transmission (Allison) torque converter are the:

   AImpeller (pump), turbine, and stator BSun gear, planet carrier, and ring gear CRotor, stator, and armature DImpeller, lockup clutch, and governor
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   Answer: A. Impeller (pump), turbine, and stator

   The engine-driven impeller (pump) throws fluid against the turbine (output), and the stator redirects the returning fluid to multiply torque. These three elements make up the converter.

4. ASE H4 Transit Bus — Brakes

   What controls the loading and unloading of the air compressor to maintain system pressure within a preset range?

   AThe governor BThe safety relief valve CThe air dryer purge valve DThe treadle valve
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   Answer: A. The governor

   The governor senses reservoir pressure and cycles the compressor between loaded (pumping) at cut-in and unloaded at cut-out, keeping supply pressure in the set range of roughly 100-125 psi.

5. ASE H5 Transit Bus — Suspension & Steering

   The primary function of the air springs (air bags) in a transit bus air suspension is to:

   ADampen spring oscillations after a bump BSteer the drive axle during turns CSupport the vehicle load and provide a cushioned ride DMaintain constant ride height as the load changes
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   Answer: C. Support the vehicle load and provide a cushioned ride

   Air springs carry the sprung weight of the bus and use compressed air as the springing medium to absorb road shock; damping is the shock absorber's job and holding a set height is the leveling valve's job.

6. ASE H6 Transit Bus — Electrical / Electronic

   A fully charged 12-volt flooded lead-acid battery that has been at rest reads approximately what open-circuit (no-load) voltage?

   A11.9 V B12.2 V C12.6 V D13.8 V
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   Answer: C. 12.6 V

   A fully charged 12V battery at rest reads about 12.6-12.7V; ~12.2V is about 50% charged and ~11.9V is discharged. Readings of 13.8V or higher only occur with a charger or alternator connected.

7. ASE H7 Transit Bus — HVAC

   The A/C compressor on most large roof-mounted transit bus HVAC systems is best described as a(n):

   AHermetically sealed scroll compressor BOpen-drive reciprocating compressor belt-driven by the engine CSealed rotary-vane compressor built into the transmission DCompressor powered only by the 12-volt chassis battery
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   Answer: B. Open-drive reciprocating compressor belt-driven by the engine

   Transit bus rooftop systems (e.g., Thermo King, Carrier) use large open-drive reciprocating compressors driven by a belt off the engine, giving the high refrigerant flow needed for a large cabin load. Sealed/hermetic units are used in small self-contained or stationary systems.

8. ASE H8 Transit Bus — PM Inspection

   Tires on the non-steering (drive and tag/pusher) axles are under the legal minimum when tread depth falls below:

   A2/32 inch B4/32 inch C6/32 inch D5/32 inch
   Show answer

   Answer: A. 2/32 inch

   49 CFR 393.75(c) requires at least 2/32 in. of tread, measured in a major groove, on every tire except front (steer) tires, which need 4/32 in. under 393.75(b); Part 396 Appendix A 10.b.(8) rejects a non-steer tire under 2/32 in. That is the legal minimum, not the CVSA roadside out-of-service point, which for non-steer tires is lower: under 1/32 in. in two adjacent grooves at three locations around the tire.

9. ASE H1 Transit Bus — CNG Engines

   Two technicians discuss a CNG leak in an enclosed maintenance bay. Technician A says leaking CNG rises and accumulates at the highest point of the space. Technician B says because CNG is heavier than air it pools on the floor. Who is correct?

   ATechnician A only BTechnician B only CBoth Technicians A and B DNeither Technician
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   Answer: A. Technician A only

   Methane's vapor density is about 0.55, so it is lighter than air and rises; Technician B is describing LPG/propane behavior, which is heavier than air.

10. ASE H2 Transit Bus — Diesel Engines

    Two technicians discuss a diesel that is hard to start and runs rough. Technician A says air leaking into the fuel on the suction side can cause this. Technician B says a loose or cracked line fitting between the tank and transfer pump can draw air in. Who is correct?

    ATechnician A only BTechnician B only CBoth Technicians A and B DNeither Technician
    Show answer

    Answer: C. Both Technicians A and B

    Air drawn into the low-pressure suction side (loose fittings, cracked lines, bad filter seals) causes hard starting, rough running, and power loss; both technicians describe valid sources.