• 40 questions

ASE H3 Study Guide

Unofficial practice for ASE's H3 Drive Train test: automatic transmission, drive shaft and drive axle on a transit bus.

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A scan tool is connected to the J1939 data link of a bus. Which data rate do J1939/11 and J1939/15 specify?

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Unofficial practice questions, not affiliated with the National Institute for Automotive Service Excellence (ASE). Bank checked October 14, 2026.

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All 40 questions with answers

Automatic transmission 28

  • A bus is held on the brakes with the transmission in gear. Which stage of torque converter operation is that? Answer: Stall: the impeller is driven but the turbine cannot turn. Source: Wikipedia, Torque converter, Operational phases. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • A bus stuck in snow is rocked between drive and reverse under power for a long time. What does the heat of continuous converter slip damage? Answer: The elastomer seals of the converter. Source: Wikipedia, Torque converter, Capacity and failure modes. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • A damaged section of CAN bus wiring is to be repaired. How are the two CAN lines best carried? Answer: As a twisted pair in a shielded cable. Source: Wikipedia, CAN bus, Layers. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
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Automatic transmission, continued

  • A dial indicator reading at the flywheel housing is the same at every point along the axis. Which form of run-out is that? Answer: Radial run-out: the part is offset from the axis but parallel to it. Source: Wikipedia, Run-out, Types. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • A new technician looks for a park position on a transit bus shift selector and finds none. Why? Answer: A bus is left in neutral with the air parking brakes set. Source: Wikipedia, Automatic transmission, P–R–N–D–L positions. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • A plain fluid coupling cannot multiply torque. Which element gives a torque converter that ability? Answer: The stator. Source: Wikipedia, Torque converter, Operational phases. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • A pressure control solenoid is driven by a pulse-width modulated signal at 25 percent duty cycle. What does that figure mean? Answer: The signal is on for a quarter of each period. Source: Wikipedia, Pulse-width modulation, Duty cycle. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • A red fluid is found dripping under a bus. Why is automatic transmission fluid usually dyed red or green? Answer: To tell it apart from motor oil and other fluids. Source: Wikipedia, Automatic transmission fluid, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • A retarder control circuit includes a hydraulic accumulator. Which kind of accumulator is by far the most common? Answer: The compressed gas (hydro-pneumatic) type. Source: Wikipedia, Hydraulic accumulator, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • A scan tool is connected to the J1939 data link of a bus. Which data rate do J1939/11 and J1939/15 specify? Answer: 250 kbit/s. Source: Wikipedia, SAE J1939, Definition. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • A transmission has several simple on/off pressure switches. What does each one detect? Answer: Whether fluid pressure is present in one hydraulic line. Source: Wikipedia, Transmission control unit, Switches. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • An external transmission seal is a radial lip seal with a garter spring. What does the spring do? Answer: Helps the sealing lip make up for wear. Source: Wikipedia, Radial shaft seal, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • At about what turbine speed, measured against the impeller, does a torque converter reach its coupling stage? Answer: About 90 percent. Source: Wikipedia, Torque converter, Operational phases. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • Before a transmission is removed from a hybrid vehicle, the high voltage cables have to be identified. Under FMVSS No. 305, how are high voltage cables outside electrical protection barriers marked? Answer: By an orange outer covering. Source: 49 CFR 571.305 (FMVSS No. 305), S5.4.1.2 and S3. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • Besides guarding against overheating, what does a modern control unit do with the transmission fluid temperature signal? Answer: It adjusts line and solenoid pressures for fluid viscosity. Source: Wikipedia, Transmission control unit, Transmission fluid Temperature sensor (TFT). Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • By the definitions of FMVSS No. 305, what does an automatic disconnect do when it is triggered? Answer: It conductively separates a high voltage source from the electric power train. Source: 49 CFR 571.305 (FMVSS No. 305), S4, Definitions. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • How is the braking effect of a hydraulic retarder varied? Answer: By changing how full its chamber is. Source: Wikipedia, Retarder (mechanical engineering), Hydraulic retarder. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • Older automatic transmissions used a centrifugal governor for a road speed signal. What do modern designs use? Answer: An electronic speed sensor. Source: Wikipedia, Automatic transmission, Hydraulic controls. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • The one-way clutch of a stator has seized, so the stator can no longer turn. Which symptom follows? Answer: Very poor efficiency in the coupling phase. Source: Wikipedia, Torque converter, Capacity and failure modes. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • Some transit buses have a dual-mode hybrid drive unit in place of a conventional transmission. What does dual-mode mean? Answer: The unit can switch between series and parallel modes. Source: Wikipedia, Hybrid electric bus, Types of hybrid vehicle drivetrain. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • The traction control system reports a slippery road to the transmission control unit. How may the control unit change its shifting? Answer: It upshifts early and may pull away in second gear. Source: Wikipedia, Transmission control unit, Traction Control System (TCS). Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • What does a sprag clutch do for a gear shift in an automatic transmission? Answer: It ends the need to time one clutch release against another apply. Source: Wikipedia, Automatic transmission, Gearsets and shifting mechanism. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • What does regenerative braking turn the traction motor of a hybrid bus into? Answer: An electric generator. Source: Wikipedia, Regenerative braking, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • What does the kick down switch tell a transmission control unit? Answer: That the accelerator has been pressed past full throttle. Source: Wikipedia, Transmission control unit, Kick down switch. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • What drives the main pump of a hydraulic automatic transmission? Answer: The torque converter housing, so it pumps whenever the engine runs. Source: Wikipedia, Automatic transmission, Hydraulic controls. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • What is ballooning of a torque converter? Answer: The housing distorted by internal pressure or inertia. Source: Wikipedia, Torque converter, Capacity and failure modes. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • What is the job of the valve body in an automatic transmission? Answer: Directing hydraulic pressure to the right bands and clutches. Source: Wikipedia, Automatic transmission, Hydraulic controls. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)
  • Where does the heat made by a hydraulic retarder go? Answer: Into the working fluid, which is sent through a cooling system. Source: Wikipedia, Retarder (mechanical engineering), Hydraulic retarder. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), A. Automatic Transmission Diagnosis and Repair (28 of 40 scored questions)

Drive shaft and universal joints 4

  • A drive shaft has a universal joint at each end, and the yokes are phased. What is the second joint phased to do? Answer: Cancel the changing angular velocity from the first joint. Source: Wikipedia, Universal joint, Double Cardan shaft. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), B. Drive Shaft and Universal Joint Diagnosis and Repair (4 of 40)
  • A noise seems to come from the transmission. Which drive line faults are outside sources of torsional vibration? Answer: A drive shaft out of balance, worn universal joints or loose center bearings. Source: US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 11, Troubleshooting Transmissions, Transfer Cases, and Differentials. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), B. Drive Shaft and Universal Joint Diagnosis and Repair (4 of 40)
  • How does a constant-velocity joint differ from a single universal joint? Answer: It keeps both shafts turning at the same speed while they run at an angle. Source: Wikipedia, Constant-velocity joint, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), B. Drive Shaft and Universal Joint Diagnosis and Repair (4 of 40)
  • What joins the two yokes of a universal joint? Answer: A cross shaft that links two hinges set at 90° to each other. Source: Wikipedia, Universal joint, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), B. Drive Shaft and Universal Joint Diagnosis and Repair (4 of 40)

Drive axle 8

  • A hypoid gearset places the pinion off the axis of the ring gear. What does that allow? Answer: A larger pinion with more contact area. Source: Wikipedia, Spiral bevel gear, Hypoid gears. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), C. Drive Axle Diagnosis and Repair (8 of 40)
  • A low floor bus has an inverted portal axle. Where does the axle sit? Answer: Below the center of the wheel, so the floor can be lower. Source: Wikipedia, Portal axle, Description. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), C. Drive Axle Diagnosis and Repair (8 of 40)
  • An axle has reduction gearing in its hubs. What does hub reduction do for the axle shafts and the differential? Answer: They carry the same power at lower torque. Source: Wikipedia, Portal axle, lead section and Description. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), C. Drive Axle Diagnosis and Repair (8 of 40)
  • Gear oils carry an API GL rating. What does a higher GL rating mean? Answer: The oil sustains more pressure without metal-to-metal contact. Source: Wikipedia, Gear oil, API ratings. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), C. Drive Axle Diagnosis and Repair (8 of 40)
  • How is the internal clearance of a tapered roller bearing set when it is mounted? Answer: By the axial position of the cone relative to the cup. Source: Wikipedia, Tapered roller bearing, Description. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), C. Drive Axle Diagnosis and Repair (8 of 40)
  • In a tapered roller wheel bearing, what is the cup? Answer: The outer ring. Source: Wikipedia, Tapered roller bearing, Description. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), C. Drive Axle Diagnosis and Repair (8 of 40)
  • Ring and pinion backlash is checked after a differential carrier is fitted. Why is some backlash specified? Answer: To allow for lubrication, thermal expansion, deflection under load and manufacturing error. Source: Wikipedia, Backlash (engineering), lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), C. Drive Axle Diagnosis and Repair (8 of 40)
  • The ring gear of a spiral bevel set is damaged and the pinion looks sound. Why are both replaced together? Answer: The two gears are manufactured and lapped as a pair. Source: Wikipedia, Spiral bevel gear, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Drive Train (Test H3), C. Drive Axle Diagnosis and Repair (8 of 40)

How this list was compiled: Our own questions, written to the three content areas of the Drive Train (Test H3) test specifications and task list in the ASE Transit Bus Study Guide (copyright 2026, https://ase.com/wp-content/uploads/ASE_TransitBus_Study_Guide.pdf, opened 2026-10-14): automatic transmission 28 of 40 scored questions, drive shaft and universal joints 4, drive axle 8. The bank holds the same 28, 4 and 8. Every fact was read in the public text the question names: Wikipedia articles on torque converters, automatic transmissions and their control units, retarders, hybrid drives, data links, universal joints, gears, gear oil, portal axles and tapered roller bearings; 49 CFR 571.305 (FMVSS No. 305) at ecfr.gov; and US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 11, in the copy at archive.org (texts fetched 2026-10-13). The sample questions printed in the study guide were not used. Licence: Questions, choices and explanations are original work of this site. NAVEDTRA 14050 is a work of the United States Navy approved for public release, and no question or example is copied from it.

How it works

This ASE H3 study guide is a practice test: 40 questions on the transit bus drive train, as many as the real test scores. It is unofficial and not affiliated with the National Institute for Automotive Service Excellence (ASE).

Read the full guide

Automatic transmission is 70 percent of H3

ASE's Transit Bus study guide gives automatic transmission diagnosis and repair 28 of the 40 scored questions. Drive axles have 8, and drive shafts and universal joints 4. H3 has no content area for a manual transmission or a clutch.

Where the drive train answers come from

Torque converter stages and faults, control unit inputs, retarders, data links, gears, gear oil, portal axles and bearings rest on Wikipedia. High voltage cable color comes from FMVSS No. 305, and drive line noise from a Navy manual.

  • Learn the torque converter by its three stages: stall, acceleration and coupling.
  • H3's task list reaches hybrid buses: identifying the high voltage system before a transmission comes out.

Questions and answers

Is there an ASE H3 practice test?

Yes. This page is a free ASE H3 practice test: 40 questions of our own, each answered with its reason and its source. They are not the questions on the real test.

How many questions are on the ASE H3 test?

ASE's 2026 Transit Bus study guide lists 50 questions in 60 minutes: 40 scored and 10 that are not counted. The recertification test is 20 questions in 30 minutes.

Is there an official ASE H3 study guide?

Yes. ASE's free Transit Bus Study Guide covers H1 to H8. Its H3 pages give the three content areas, the task list and eight sample questions. None of those sample questions is used here.

Is H3 required for Master Transit Bus Technician status?

Yes. ASE's study guide stars H3 through H8 as required, together with one engine test, H1 or H2.

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