The ASE T2 Diesel Engines test is one of the core certifications in the Medium/Heavy Truck (T-Series). Pass it along with the other T-Series tests and you’re on your way to Master Medium/Heavy Truck Technician status. It also tells every shop you apply to that you can do more than change oil.
This guide breaks down what’s on the test, where the points are, and how to study so your time goes where the questions are.
The T2 test at a glance
The T2 has 40 scored questions across seven content areas. ASE may also include a few extra unscored questions it’s testing for future exams. You won’t know which ones they are, so treat every question like it counts.
| Content area | Scored questions |
|---|---|
| A. General Engine Diagnosis | 7 |
| B. Cylinder Head and Valve Train | 4 |
| C. Engine Block | 3 |
| D. Lubrication System | 4 |
| E. Cooling System | 7 |
| F. Air Induction, Exhaust Systems and Engine Brakes | 7 |
| G. Fuel System | 8 |
| Total | 40 |
Where the points are: Fuel, Air Induction/Exhaust, Cooling, and General Diagnosis add up to 29 of the 40 questions. Head, block, and lube are only 11 combined. If your study time is limited, spend most of it on diagnosis, air, fuel, and cooling.
A. General Engine Diagnosis (7 questions)
This section tests whether you can read the engine before you pick up a wrench: fluid levels and condition, leaks, noises, vibration, no-start and hard-start complaints, power problems, and pulling codes and live data.
- Know your smoke colors. Black smoke means too much fuel for the air available, so think air restriction, boost leaks, a bad turbo, or overfueling. Blue smoke means oil is being burned. White smoke usually means fuel that isn’t burning completely, often a cold engine, low compression, or timing problems. White smoke can also be coolant getting into the cylinders.
- Diagnose in order. Expect “what should the technician do first?” questions. The answer is almost always the simplest, least invasive check: verify the complaint, check fluids, pull codes, then test.
- Codes point you somewhere. They don’t replace testing. A code tells you which circuit or system to look at. It doesn’t tell you which part to replace.
B. Cylinder Head and Valve Train (4 questions)
This section covers head removal and inspection, checking for cracks and warpage, valves, guides, seats and springs, injector sleeves and protrusion, overhead cams, and adjusting valve bridges and valve lash.
- Know that a valve bridge (crosshead) is adjusted before setting valve clearance on engines that have them.
- Know how head warpage is checked: a precision straightedge and feeler gauge across the mating surface, compared against the manufacturer’s spec.
- Injector sleeve problems can show up as coolant in the fuel or fuel in the coolant. Remember that connection.
C. Engine Block (3 questions)
This is the biggest task list and the fewest questions. It covers crankcase pressure testing, liners and liner height, crankshaft and bearings, gear train timing, pistons and rings, piston cooling jets, the vibration damper, and the flywheel housing.
- Crankcase pressure (blow-by): high readings point to worn rings or liners. They can also come from other sources pushing air into the crankcase, like a leaking turbocharger seal or air compressor.
- Liner protrusion (height) is measured and has to be within spec, or you’ll have head gasket problems.
- A damaged or out-of-spec vibration damper can lead to crankshaft damage. Know that it’s an inspection item.
D. Lubrication System (4 questions)
This section covers oil pressure testing and sensors, oil level, condition and consumption, the oil pump and pickup, pressure regulator and relief valves, the oil cooler, turbo lubrication, and choosing the right oil.
- Confirm a low oil pressure reading with a mechanical gauge before condemning the engine. The sensor or gauge could be the problem.
- Know what a stuck regulator or relief valve does to oil pressure, both when it’s stuck open and when it’s stuck closed.
- Coolant in the oil can come from an oil cooler failure. Don’t jump straight to a head gasket.
E. Cooling System (7 questions)
This section covers coolant type, level and condition, temperature sensors, belts and tensioners, thermostats, flushing and bleeding, coolant filters, water pumps, radiator and cap pressure testing, and fan drives and shrouds.
- A refractometer is the accurate way to check coolant freeze protection.
- Don’t mix coolant types. Know the difference between conventional coolant that needs supplemental coolant additives (SCAs) and extended-life coolant.
- Overheating questions often come down to airflow: a missing fan shroud, a fan clutch that isn’t engaging, or plugged radiator fins.
- A thermostat stuck open causes an engine that runs cold, not one that overheats.
F. Air Induction, Exhaust Systems and Engine Brakes (7 questions)
This section covers intake restriction and leak tests, boost tests, exhaust back pressure, turbochargers (including variable geometry), charge air coolers, exhaust aftertreatment, intake heaters and glow plugs, EGR, and engine brakes.
- Test intake restriction at full load and rated speed, because that’s when the engine pulls the most air. A test at idle won’t show a restriction.
- A leaking charge air cooler means low boost, low power, and black smoke. Know how it’s pressure tested.
- High exhaust back pressure, for example from a plugged DPF, causes low power and high exhaust temperatures.
- Know the basics of how compression (engine) brakes work and when they’re adjusted.
G. Fuel System (8 questions)
This is the biggest section. It’s split between the fuel supply system (tanks, lines, transfer pump, filters, water separators, priming and bleeding) and the electronic fuel management system (circuits, sensors, scan tools, unit injectors, HEUI, and common rail).
- Restriction on the suction side of the transfer pump and air getting into the supply system are classic causes of low power and hard starting.
- Know your electrical basics: voltage drop testing, measuring resistance, and checking power and grounds before replacing a module.
- A cylinder cutout/contribution test with diagnostic software is the fastest way to find a weak cylinder or bad injector.
- Common rail systems run extremely high pressures. Follow the safety procedures before opening any high-pressure line.
Try a few practice questions
1. A diesel engine produces black smoke under load. Which of these is the LEAST likely cause?
A. Restricted air filter
B. Leaking charge air cooler
C. Thermostat stuck open
D. Damaged turbocharger
Answer: C. A stuck-open thermostat makes the engine run cold. The other three all reduce airflow, which causes black smoke.
2. Crankcase pressure is above spec. Technician A says worn piston rings could be the cause. Technician B says a leaking turbocharger seal could be the cause. Who is right?
A. A only
B. B only
C. Both A and B
D. Neither A nor B
Answer: C. Anything that pushes combustion gases or pressurized air into the crankcase raises crankcase pressure.
3. Which tool gives the most accurate reading of coolant freeze protection?
A. Hydrometer
B. Refractometer
C. Test strips
D. Infrared thermometer
Answer: B. A refractometer is the most accurate. Test strips are useful for checking SCA levels.
4. An intake air restriction test is most accurate when performed:
A. At low idle
B. At high idle with no load
C. At rated speed under full load
D. With the engine off
Answer: C. Restriction shows up when airflow is highest.
5. An electronically controlled engine has a miss at idle. What is the most efficient first test?
A. Replace all injectors
B. Perform a cylinder cutout/contribution test
C. Pull the cylinder head
D. Replace the fuel filters
Answer: B. It tells you which cylinder is the problem before you spend money on parts.
A simple 4-week study plan
- Week 1: General diagnosis and the fuel system. That’s 15 questions’ worth.
- Week 2: Air induction, exhaust, aftertreatment, and engine brakes.
- Week 3: Cooling and lubrication.
- Week 4: Head, valve train, and block, then full-length practice tests. Review every question you miss until you understand why the right answer is right.
Read the “Technician A / Technician B” questions slowly. Decide whether each statement is true on its own before you look at the answer choices.
Always check the official ASE Medium/Heavy Truck study guide at ase.com for the current task list before your test date. ASE updates its specifications from time to time.
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Related: 5 Careers in the Diesel Industry
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