• 60 questions

ASE Certified Diesel Mechanic Practice Test

Unofficial T2 Diesel Engines practice in ASE's eight content areas, from diagnosis to engine brakes, every answer with its source.

At what temperature does diesel exhaust fluid (DEF) freeze?

Pick an answer, then press Check answer. Then you see Correct or Not quite, with the reason. Keys: A to D pick, Enter checks.

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Exam mode: 55 questions, 90 minutes.

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Unofficial practice questions, not affiliated with the National Institute for Automotive Service Excellence (ASE). Bank checked October 12, 2026.

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All 60 questions

General engine diagnosis 12

  • A crankcase pressure test reads high. What is blowby? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
  • A diesel engine draws oil mist from a failed turbocharger, overspeeds and will not shut down with the key. What is this called? Wikipedia, Diesel engine runaway. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
  • A fleet sends engine oil samples to a laboratory. Which of these is one of the three parts of an oil analysis? Wikipedia, Oil analysis. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
  • A truck is brought in for a power complaint and run on a dynamometer. What does a dynamometer measure? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
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General engine diagnosis, continued

  • A truck puts out black smoke under load. What is black diesel smoke made of? Wikipedia, Diesel exhaust, Variation with engine conditions. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
  • A turbocharger's seals fail and oil leaks into the exhaust system. Which smoke color does that often cause? Wikipedia, Turbocharger, Safety. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
  • A visual inspection finds that an emission control device has been removed from a truck engine. What does 40 CFR 1068.101(b)(1) say about that? 40 CFR 1068.101 (ecfr.gov). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
  • At what temperature does diesel exhaust fluid (DEF) freeze? Wikipedia, Diesel exhaust fluid, Operation in winter time. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
  • What does an exhaust back pressure test measure? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
  • What is diesel exhaust fluid (DEF) made of? Wikipedia, Diesel exhaust fluid. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
  • Which SAE standard defines the vehicle network a diagnostic tool reads on a heavy truck, and is regarded as the replacement for J1708 and J1587? Wikipedia, SAE J1939. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis
  • Which tool reads the specific gravity of the coolant to show its freezing point? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), General engine diagnosis

Cylinder head and valve train 4

  • A technician checks camshaft drive gear backlash. What is backlash? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Cylinder head and valve train
  • In an overhead valve engine, what does the rocker arm do? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Cylinder head and valve train
  • TM 9-8000 defines a tappet as an adjusting screw in the valve train. What does it adjust? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Cylinder head and valve train
  • What does the head gasket seal? Wikipedia, Head gasket. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Cylinder head and valve train

Engine block 5

  • Besides sealing, what do piston rings do with the heat the piston absorbs? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 3-6. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Engine block
  • The coolant side of a diesel cylinder liner is pitted. What causes this damage? Wikipedia, Cavitation, Engines. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Engine block
  • What is a cam-ground piston? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 3-5. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Engine block
  • Which measuring tool is a strip of soft material that is crushed between a bearing and its journal to show the clearance? Wikipedia, Plastigauge. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Engine block
  • Why is a four-ring piston with three compression rings common in diesel engines? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 3-6. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Engine block

Lubrication and cooling systems 7

  • A radiator pressure cap has two spring-loaded valves. What does the larger one, the pressure valve, do? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 9-10. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Lubrication and cooling systems
  • In a bypass oil filter system, where does the filtered oil go? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 8-13. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Lubrication and cooling systems
  • Some trucks have an expansion tank in series with the upper radiator hose. What is it for? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 9-11. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Lubrication and cooling systems
  • Some turbocharger center sections are water-cooled. What is one reason? Wikipedia, Turbocharger, Center hub rotating assembly. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Lubrication and cooling systems
  • The thermostat is closed on a cold engine. What does the coolant bypass let the water pump do? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 9-9. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Lubrication and cooling systems
  • What type of pump is the engine water pump? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 9-7. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Lubrication and cooling systems
  • Where is the oil strainer screen usually located? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 8-12. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Lubrication and cooling systems

Air induction and exhaust systems 7

  • How does a variable-geometry turbocharger change its response as conditions change? Wikipedia, Variable-geometry turbocharger. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Air induction and exhaust systems
  • How does exhaust gas recirculation (EGR) cut NOx emissions? Wikipedia, Exhaust gas recirculation. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Air induction and exhaust systems
  • Technician A says ash builds up in a diesel particulate filter because it cannot be turned into a gas. Technician B says the ash is a byproduct of the oil the engine consumes. Who is right? Wikipedia, Diesel particulate filter, Maintenance. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Air induction and exhaust systems
  • What does a selective catalytic reduction (SCR) system turn nitrogen oxides into? Wikipedia, Selective catalytic reduction. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Air induction and exhaust systems
  • What does regeneration do in a diesel particulate filter (DPF)? Wikipedia, Diesel particulate filter. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Air induction and exhaust systems
  • What is a charge air cooler (intercooler)? Wikipedia, Intercooler. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Air induction and exhaust systems
  • What is the primary function of a turbocharger wastegate? Wikipedia, Wastegate. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Air induction and exhaust systems

Fuel system 17

  • A small, controlled amount of fuel seeps between the nozzle valve and its body and returns through the overflow lines. What is that seepage for? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 5, multiple unit injection (figures 5-7 and 5-8). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • A truck will not run on a very cold morning and the fuel filters are plugged with a waxy solid. What happened to the fuel? Wikipedia, Winter diesel fuel. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • On a pump-line-nozzle system, what lifts the nozzle valve off its seat to start injection? US Army TM 9-8000, Principles of Automotive Vehicles (1985), chapter 5, multiple unit injection (figures 5-7 and 5-8). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • Technician A says the secondary fuel filter sits between the supply pump and the injection pump. Technician B says the secondary filter has a coarser medium than the primary filter. Who is right? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 5-35. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • Under 49 CFR 393.65, which of these is not allowed while a combination of vehicles is in motion? 49 CFR 393.65 (ecfr.gov). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • Under the federal ULSD standard, a diesel fuel must have an aromatic content of 35 percent or less, or a cetane index of at least what? 40 CFR 1090.305 (ecfr.gov). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • What is a common rail fuel system built around? Wikipedia, Common rail. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • What is the air valve on a diesel fuel filter for? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 5-36. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • What is the maximum sulfur content of ultra-low-sulfur diesel fuel (ULSD) under the federal standard? 40 CFR 1090.305 (ecfr.gov). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • What powers the high-pressure injection in a hydraulically actuated electronic unit injector (HEUI) system? Wikipedia, Unit injector, Hydraulically actuated electronic (HEUI) development and applications. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • What typically lubricates and cools a unit injector? Wikipedia, Unit injector. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • Where is the primary fuel filter usually located? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 5-35. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • Why do all diesel engines need a governor? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 5-24. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • Why does TM 9-8000 call careful filtration especially necessary for diesel fuel? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 5-34. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • Why does water collect at the bottom of a diesel fuel filter bowl, where it can be drained? Wikipedia, Fuel filter, Filters for foreign liquids. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • Why is more fuel sent to the injection pump than the engine burns? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 5-20. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system
  • Why must a fuel supply (transfer) pump feed the injection pump? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 5-20. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Fuel system

Starting and charging systems 5

  • A truck has sat through a hard freeze and its battery case is frozen. Should it be jump-started? Wikipedia, Jump start (vehicle), Procedures. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Starting and charging systems
  • Besides a hydrometer reading of each cell, what else can gauge the state of charge of a lead-acid battery? Wikipedia, Lead–acid battery, Measuring the charge level. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Starting and charging systems
  • Jumper cables are connected in a recommended sequence. What is the sequence meant to prevent? Wikipedia, Jump start (vehicle), Procedures. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Starting and charging systems
  • What is sulfation in a storage battery? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Starting and charging systems
  • What two jobs does the solenoid on a starter do? Wikipedia, Starter (engine). Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Starting and charging systems

Engine brakes 3

  • How does an exhaust brake slow a diesel engine? Wikipedia, Exhaust brake. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Engine brakes
  • In the compression release engine brake that TM 9-8000 describes, which part is mounted over the exhaust valve to open it? US Army TM 9-8000, Principles of Automotive Vehicles (1985), paragraph 5-40. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Engine brakes
  • When does a compression release engine brake open the exhaust valves? Wikipedia, Compression release engine brake. Outline: ASE Medium/Heavy Truck Study Guide (copyright 2026), Diesel Engines (Test T2), Engine brakes

How this list was compiled: Our own questions, written to the eight content areas of the Diesel Engines (Test T2) test specifications and task list in the ASE Medium/Heavy Truck Study Guide (copyright 2026, https://ase.com/wp-content/uploads/ASE_MedHeavyTruck_Study_Guide.pdf, read 2026-10-12): general engine diagnosis 11 of 55 scored questions, cylinder head and valve train 4, engine block 5, lubrication and cooling 6, air induction and exhaust 6, fuel system 16, starting and charging 4, engine brakes 3. The bank holds 12, 4, 5, 7, 7, 17, 5 and 3 in that order. Every fact was read on 2026-10-12 in the public text the question names: US Army TM 9-8000, Principles of Automotive Vehicles (1985, the copy at archive.org); 40 CFR 1090.305 and 1068.101 and 49 CFR 393.65 at ecfr.gov; and Wikipedia articles on current diesel fuel, air and aftertreatment systems. The sample questions printed in the study guide were not used. Licence: Questions, choices and explanations are original work of this site. TM 9-8000 is a work of the United States Army approved for public release, and no question or example is copied from it.

How it works

Sixty questions of our own on truck diesel engines, in ASE's eight T2 content areas. This free ASE certified diesel mechanic practice test is unofficial: the National Institute for Automotive Service Excellence (ASE) does not sponsor or endorse it.

Read the full guide

Eight content areas, 55 scored questions

ASE's T2 specifications give the fuel system 16 questions and general engine diagnosis 11. Lubrication and cooling has 6, air induction and exhaust 6, engine block 5, cylinder head and valve train 4, starting and charging 4 and engine brakes 3.

Where the answers come from

Engine construction, oiling, cooling and pump-line-nozzle injection come from the Army manual TM 9-8000. Fuel sulfur, tampering and fuel line rules come from 40 CFR and 49 CFR. Common rail, unit injectors, turbocharger controls and aftertreatment rest on Wikipedia.

A timed round

The real T2 test allows 90 minutes. Exam mode draws 55 questions, the scored count, against that clock. Every ASE certification practice test here is free, T2 included.

  • Know what each aftertreatment part does: the DPF traps soot, SCR with DEF converts NOx, and EGR lowers combustion temperature.

Questions and answers

How many questions are on the ASE T2 test?

Sixty-five, in 90 minutes, by ASE's 2026 study guide. Ten of them are not counted for score, which leaves 55 scored. Recertification is a shorter test: 28 questions in 45 minutes.

Is there a free ASE certified diesel mechanic T2 practice test?

This one. The ASE diesel T2 practice test on this page costs nothing and asks for no sign-up, in practice mode, in the timed round and on paper. Its questions were written for this site and are not ASE's.

What does the ASE T2 series practice test cover?

The eight content areas of the T2 task list, from general engine diagnosis to engine brakes. T2 is one test of ASE's Medium/Heavy Truck series: brakes, drive train, suspension and the rest have tests of their own.

Does T2 count toward Master Medium/Heavy Truck Technician?

Yes. In ASE's study guide Diesel Engines (T2) carries the mark of a test required for Master Medium/Heavy Truck Technician recognition. Certification also takes two years of relevant work experience.

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