• 50 questions

ASE H2 Practice Test

Unofficial practice for ASE's H2 Diesel Engines test for transit bus technicians, engine diagnosis to starting and charging.

Which instrument measures the concentration of coolant in water from the way the sample bends light?

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Unofficial practice questions, not affiliated with the National Institute for Automotive Service Excellence (ASE). Bank checked October 13, 2026.

Next step All eight H tests: transit bus practice

All 50 questions

General engine diagnosis 14

  • A boost gauge is connected for an intake manifold pressure test. What does a boost gauge read? Wikipedia, MAP sensor, Common confusion with boost sensors and gauges. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • A bus has a smoky exhaust. Technician A says smoke always means a faulty injection pump or nozzle. Technician B says lack of air, overloading, oil burning or low compression can also be the cause. Who is right? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Diesel Fuel Injection Systems, Troubleshooting. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • A hollow, bell-like knock is heard only while the engine is cold. What is it, and how serious is it by the Navy manual? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, Engine Noises. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
Show all 50 questions (47 more)

General engine diagnosis, continued

  • A shop is asked to fit a part that disables an emission control on a diesel engine. What does 40 CFR 1068.101(b)(2) say? 40 CFR 1068.101, paragraph (b)(2), Defeat devices. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • An engine burns too much oil. With the head off, heavy carbon is found on the undersides of the intake valves. What does that indicate? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, Excessive Oil Consumption. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • An engine with an injection pump and high-pressure lines runs unevenly. The line nut is loosened at each cylinder in turn. At one cylinder, loosening the nut changes nothing. What has been found? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Diesel Fuel Injection Systems, Troubleshooting. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • An exhaust gas temperature gauge (pyrometer) is fitted for an exhaust temperature test. What kind of sensor does it read? Wikipedia, Exhaust gas temperature gauge, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • The crankcase breather is restricted and pressure builds inside the engine. What can that lead to? Wikipedia, Crankcase ventilation system, Source of crankcase gases. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • The engine oil is thin and diluted with fuel. Which fuel system fault does the Navy manual link with engine oil dilution? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Diesel Fuel Injection Systems, injector inspection. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • The fuel supplier's ticket says the bus fuel is B20. What does that mean? Wikipedia, Biodiesel, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • Injection is blamed for poor running. Which of these is on the Navy manual's list of the most likely causes, checked before any injection component? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Diesel Fuel Injection Systems. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • Under 40 CFR 1068.120(g), on rebuilding engines, emission-related codes from the onboard monitoring system must not be erased or reset until what has been done? 40 CFR 1068.120, paragraph (g). Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • What is a listening rod used for in engine diagnosis? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, Engine Noises. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)
  • Which instrument measures the concentration of coolant in water from the way the sample bends light? Wikipedia, Refractometer, lead section and Water. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), A. General Engine Diagnosis (14 of 50 scored questions)

Cylinder head and valve train 4

  • Heavy-duty engines often have rotators on the exhaust valves. What are they for? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 3, Valve Rotators. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), B. Cylinder Head and Valve Train Diagnosis and Repair (4 of 50)
  • Rocker arms and shafts are being installed on the cylinder head. Where must the oil holes in the shafts face? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, Rocker Arm Servicing. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), B. Cylinder Head and Valve Train Diagnosis and Repair (4 of 50)
  • The valves have been reconditioned and the head is back on. What is done with the valve adjusting screws before the engine is rotated? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, Valve Adjustments. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), B. Cylinder Head and Valve Train Diagnosis and Repair (4 of 50)
  • Why is a new valve seat insert chilled in dry ice before it is driven into the cylinder head? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, valve seat inserts. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), B. Cylinder Head and Valve Train Diagnosis and Repair (4 of 50)

Engine block 4

  • By the Navy manual, how far may a crankshaft journal be tapered or out of round before it must be reground? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, Crankshaft Journal Check. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), C. Engine Block Diagnosis, Repair, and Overhaul (4 of 50)
  • The cylinders are worn past the point where honing will clean them up. What is done, by the Navy manual? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, Cylinder Refinishing. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), C. Engine Block Diagnosis, Repair, and Overhaul (4 of 50)
  • Directly driven timing gears are being meshed. One gear has marks on two adjacent teeth and the other a mark on one tooth. How do the marks line up? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, Valve Timing. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), C. Engine Block Diagnosis, Repair, and Overhaul (4 of 50)
  • How is crankshaft end play measured, by the Navy manual? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, Crankshaft Installation. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), C. Engine Block Diagnosis, Repair, and Overhaul (4 of 50)

Lubrication and cooling systems 7

  • A turbocharger is being mounted. Where must its oil outlet be located, by the Navy manual? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Air Induction System, Turbochargers. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), D. Lubrication and Cooling Systems Diagnosis and Repair (7 of 50)
  • An oil temperature regulator is fitted with the oil cooler. What does it use to control oil temperature, by TM 9-8000? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 8-14, Oil Coolers. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), D. Lubrication and Cooling Systems Diagnosis and Repair (7 of 50)
  • How short a loss of lubricating oil can cause a turbocharger failure, by the Navy manual? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Air Induction System, Turbochargers. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), D. Lubrication and Cooling Systems Diagnosis and Repair (7 of 50)
  • Oil pressure is low and the bearings are sound. Which other cause does the Navy manual list? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 3, Engine Troubleshooting and Overhaul, Low Oil Pressure. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), D. Lubrication and Cooling Systems Diagnosis and Repair (7 of 50)
  • The oil specified for a bus engine is SAE 15W-40. What does the 15W part of the grade describe? Wikipedia, Motor oil, SAE J300 viscosity grades. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), D. Lubrication and Cooling Systems Diagnosis and Repair (7 of 50)
  • One serpentine belt drives the alternator, water pump and other accessories. What may keep it under tension? Wikipedia, Serpentine belt, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), D. Lubrication and Cooling Systems Diagnosis and Repair (7 of 50)
  • What opens the valve of a wax-pellet cooling system thermostat? Wikipedia, Wax thermostatic element, lead section and Automotive thermostats. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), D. Lubrication and Cooling Systems Diagnosis and Repair (7 of 50)

Air induction and exhaust systems 6

  • A turbocharger has failed. Before the replacement is fitted, what does the Navy manual call essential? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Air Induction System, Turbochargers. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), E. Air Induction and Exhaust Systems Diagnosis and Repair (6 of 50)
  • An exhaust pipe on a bus has been wrapped and patched to seal a leak. What does 49 CFR 393.83(f) say about that repair? 49 CFR 393.83, paragraph (f). Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), E. Air Induction and Exhaust Systems Diagnosis and Repair (6 of 50)
  • Ether must be used to start an engine in an emergency. When is it sprayed into the air intake, by the Navy manual? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Cold Starting Devices. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), E. Air Induction and Exhaust Systems Diagnosis and Repair (6 of 50)
  • How does a manifold flame heater help a diesel engine start in the cold? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Cold Starting Devices. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), E. Air Induction and Exhaust Systems Diagnosis and Repair (6 of 50)
  • How does the Navy manual test a glow plug? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Cold Starting Devices. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), E. Air Induction and Exhaust Systems Diagnosis and Repair (6 of 50)
  • What does a diesel oxidation catalyst (DOC) do to the exhaust? Wikipedia, Catalytic converter, Diesel engines. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), E. Air Induction and Exhaust Systems Diagnosis and Repair (6 of 50)

Fuel system 11

  • A crankshaft position sensor may be inductive or Hall-effect. What can a Hall-effect sensor detect that an inductive sensor cannot? Wikipedia, Crankshaft position sensor, Types of sensors. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)
  • A diagnostic tool is connected to a bus with an SAE J1939 data link. Which network specification does J1939 include? Wikipedia, SAE J1939, Definition. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)
  • A digital multimeter shows a voltage drop across a connector in an injector circuit. Why is voltage drop across contacts and connectors undesirable? Wikipedia, Voltage drop, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)
  • A scan tool shows an actuator driven by a pulse-width modulated signal at 25% duty cycle. What does duty cycle describe? Wikipedia, Pulse-width modulation, Duty cycle. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)
  • An older bus uses SAE J1708 together with SAE J1587. Which part of the data link does J1708 make up? Wikipedia, SAE J1587, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)
  • In an electronic unit injector, the plunger is on its way down and fuel is spilling to the return duct. What makes injection begin? Wikipedia, Unit injector, Operation principle. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)
  • In the Navy manual's field test of a distributor-type injection pump, the vacuum on the suction side reads over 10 inches of mercury at high idle. What is checked? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Diesel Fuel Injection Systems, Troubleshooting. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)
  • On a tester, an injection nozzle opens more than 50 psi below its specified opening pressure. How is the pressure corrected, by the Navy manual? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Diesel Fuel Injection Systems, Nozzle Troubleshooting. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)
  • What does the malfunction indicator light (MIL) on the dash report? Wikipedia, Check engine light, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)
  • What is a breakout box used for when an electronic engine control circuit is tested? Wikipedia, Breakout box, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)
  • Why are hands kept away from the tip of an injector while it is being tested? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Diesel Fuel Injection Systems, injector testing. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), F. Fuel System Diagnosis and Repair (11 of 50)

Starting and charging systems 4

  • A battery carries an ampere-hour (Ah) rating. Over what discharge is that rating taken? Wikipedia, Automotive battery, Amp hours (Ah). Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), G. Starting and Charging System Diagnosis and Repair (4 of 50)
  • A battery is to be charged while it is still in a vehicle that has an electronic control unit. Which precaution does the Navy manual give? US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992), chapter 5, Fuel System Overhaul, Servicing and Precautions. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), G. Starting and Charging System Diagnosis and Repair (4 of 50)
  • An old DC generator needed a cutout relay to isolate it from the battery at low speed. What does that job in an alternator? Wikipedia, Alternator (automotive), Advantages over dynamos. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), G. Starting and Charging System Diagnosis and Repair (4 of 50)
  • What is a trickle charger meant to do? Wikipedia, Battery charger, lead section. Outline: ASE Transit Bus Study Guide (copyright 2026), Diesel Engines (Test H2), G. Starting and Charging System Diagnosis and Repair (4 of 50)

How this list was compiled: Our own questions, written to the seven content areas of the Diesel Engines (Test H2) 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, read 2026-10-13): general engine diagnosis 14 of 50 scored questions, cylinder head and valve train 4, engine block 4, lubrication and cooling 7, air induction and exhaust 6, fuel system 11 (mechanical 3, electronic 8), starting and charging 4. The bank holds the same 14, 4, 4, 7, 6, 11 and 4. Every fact was read on 2026-10-13 in the public text the question names: US Navy NAVEDTRA 14050, Construction Mechanic, Advanced (1992) and US Army TM 9-8000, Principles of Automotive Vehicles (1985), both in the copies at archive.org; 40 CFR 1068.101 and 1068.120 and 49 CFR 393.83 at ecfr.gov; and Wikipedia articles on electronic engine controls, data links, oils and batteries. The sample questions printed in the study guide were not used. Licence: Questions, choices and explanations are original work of this site. NAVEDTRA 14050 and TM 9-8000 are works of the United States Navy and Army approved for public release, and no question or example is copied from them.

How it works

This free ASE H2 practice test puts 50 diesel engine questions to transit bus technicians, one for each scored question of the real test. It is unofficial, written for this site, and not affiliated with the National Institute for Automotive Service Excellence (ASE).

Read the full guide

Seven content areas, 50 scored questions

ASE's Transit Bus study guide gives general engine diagnosis 14 questions and the fuel system 11, of which 8 are on electronic components and 3 on mechanical ones. Lubrication and cooling has 7, air induction and exhaust 6, and cylinder head, engine block, and starting and charging 4 each.

Where the answers come from

Engine noises, valve and crankshaft work, turbocharger care, cold starting aids and injection tests come from Navy and Army manuals, older than current buses. Electronic injectors, data links and emission rules rest on Wikipedia and federal regulations.

Timed like the real test

H2 allows 75 minutes. The timed round asks all 50 questions against that clock.

  • General engine diagnosis is 28 percent of H2. Begin with noises, smoke, oil consumption and fuel supply checks.
  • Most fuel questions are on electronic components: injector solenoids, sensors, data links and meter readings.

Questions and answers

How many questions are on the ASE H2 test?

Sixty, in 75 minutes, by ASE's 2026 Transit Bus study guide. Fifty are scored and ten gather statistics for future tests. The recertification test is 25 questions in 30 minutes.

Are these real ASE H2 test questions?

No. Every question was written for this site from ASE's published task list and public sources. None comes from the H2 test or from the sample questions in ASE's study guide, so a score here is practice only.

Do I need H2 to be a Master Transit Bus Technician?

H2 or H1. ASE's study guide says tests H3 through H8 are required, along with H1 (compressed natural gas engines) or H2 (diesel engines), for ASE Certified Master Transit Bus Technician status.

How is H2 different from the truck diesel test, T2?

ASE lists H2 in its Transit Bus series, with 50 scored questions in seven content areas. T2 has 55 in eight, one of them engine brakes. For trucks, see the ASE T2 practice test.

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