Five free practice questions on general engine diagnosis: content area A of the ASE T2 Diesel Engines test, 11 of its 55 scored questions (20%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.
01The questions
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A driver says a tractor loses power climbing long grades with a loaded trailer. On an empty test drive around the block it feels normal, and the ECM has no active or inactive fault codes. What should the technician do to verify the complaint?
- Measure fuel pressure at idle with the truck parked
- Replace the fuel filters, then repeat the empty drive
- Test it under full load on a road test or dynamometer
- Run a cylinder cutout test at idle in the shop
Show the answer
C. Correct. A low-power complaint has to be reproduced under the conditions that cause it: full load, on a loaded road test up a grade or a chassis dynamometer pull, with a scan tool recording data such as boost, fuel pressure and fueling. An empty drive asks for a fraction of the engine's power, so a full-load fault can hide.
Why not the others
A. At idle the engine uses little fuel, so a supply that falls short only at full-load flow can read normal. The complaint has to be reproduced, and the readings taken, under full load.
B. Changing parts before the complaint is verified is guesswork, and another empty drive still would not load the engine enough to show the problem. Verify it under full load first.
D. A cutout test at idle finds a weak cylinder, but it does not reproduce a power loss that appears only under heavy load. Verify the complaint under full load first.
ID T2-A-003 · Task T2-A-1 (ASE task list)
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A knock comes from a truck's diesel at idle. It is loud while the air system builds pressure, stops each time the governor cuts out and returns when it cuts back in. The scan tool's cylinder cutout test does not change it, and oil pressure meets the manufacturer's specification. Which of these is the cause?
- A worn water pump shaft bearing
- A worn connecting rod bearing in the engine
- Excessive clearance on an exhaust valve
- A worn engine-driven air brake compressor
Show the answer
D. Correct. The governor loads the compressor while the system builds pressure and unloads it at cut-out, so a knock that comes and goes exactly with the governor is the compressor, typically a worn rod bearing or piston knocking while it pumps. The unchanged cutout test and normal oil pressure point away from the engine's own bottom end.
Why not the others
A. A worn water pump bearing makes a steady growl or rumble that follows engine speed regardless of the air system. A knock that stops at governor cut-out follows compressor loading.
B. A rod bearing knock would not stop and start with the governor, and it would usually change when its cylinder is cut out. This knock follows compressor loading.
C. Valve clearance noise is a tick at half engine speed that stays the same whatever the air system is doing. This knock stops each time the governor unloads the compressor.
ID T2-A-011 · Task T2-A-5 (ASE task list)
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A water manometer at the turbocharger inlet shows air intake restriction above the manufacturer's limit at rated speed and full load. Any of these could cause the high reading EXCEPT:
- a cracked charge air cooler tube.
- snow packed into the air inlet screen.
- a hose whose inner wall has collapsed.
- an element loaded with dust.
Show the answer
A. Correct. The charge air cooler is on the pressure side, after the compressor, so a crack there loses boost but cannot raise the restriction measured at the turbocharger inlet. Snow in the inlet, a collapsed hose and a dust-loaded element all restrict the air before it reaches the compressor.
Why not the others
B. Snow packed into the inlet screen blocks air ahead of the filter, raising the restriction the manometer reads; inlets are checked for it in winter.
C. A hose whose inner wall has collapsed narrows the passage on the suction side, so the manometer reads higher restriction even if the outside of the hose looks fine.
D. A dust-loaded element is the most common cause of high restriction; it is why restriction is measured to decide when the element is changed.
ID T2-A-016 · Task T2-A-8 (ASE task list)
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A truck's diesel has an intake air heater (grid heater) in its intake. Why does the manufacturer warn against spraying ether starting fluid into the intake to help a cold start?
- Ether cools the air below what the grid can heat
- Ether keeps the ECM from metering fuel
- The hot grid can set it off in the intake
- Ether sets an intake air temperature fault
Show the answer
C. Correct. Ether ignites at a low temperature, and the energized grid sits in the air stream it would be drawn through, so it can ignite the ether in the intake and cause a backfire that damages the intake or injures someone nearby. Use the heater as designed, or only the starting aid the manufacturer approves.
Why not the others
A. Any cooling from evaporating ether is small, and the grid heats whatever air passes it; cooling is not the reason for the warning. The hazard is the hot grid igniting the ether.
B. The ECM meters fuel from its own inputs and does not sense ether. The danger is the hot grid igniting the ether in the intake.
D. Ether does not make the intake air temperature sensor set a fault. The warning is that the energized grid can ignite ether in the intake.
ID T2-A-025 · Task T2-A-12 (ASE task list)
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Any of these could leave the diesel exhaust fluid (DEF) in a truck's tank unfit to use EXCEPT:
- diesel fuel poured into the DEF tank by mistake.
- rinse water left in the tank after it was cleaned.
- DEF stored for months in drums in a hot yard.
- DEF that froze in the tank overnight and thawed.
Show the answer
D. Correct. DEF freezes in very cold weather, but freezing and thawing do not change it, so once thawed it can be used; heated systems thaw it in service. Dilution, heat-aged DEF and contamination all leave fluid the SCR system cannot use properly.
Why not the others
A. Fuel contaminates DEF and damages the DEF pump, lines and doser; a tank with fuel in it is drained and flushed as the manufacturer directs.
B. Water dilutes the urea below the strength the SCR system needs, so NOx conversion falls; DEF must be at its specified concentration.
C. Heat breaks down the urea in DEF over time, so DEF stored hot for months can fall out of specification; its shelf life shortens as storage temperature rises.
ID T2-A-031 · Task T2-A-16 (ASE task list)
02Answer key
| Question | Answer |
|---|---|
| Q1 | C |
| Q2 | D |
| Q3 | A |
| Q4 | C |
| Q5 | D |
03What area A covers
This content area covers the diagnosis that comes before any repair on a truck or tractor diesel: verifying the complaint under load, identifying the engine for service information, leaks, harness routing, noise and smoke, fuel quality, intake, boost, back pressure and crankcase pressure tests, starting and performance complaints, coolant, oil and DEF checks, scan tool data and calibrations, and spotting tampered emission parts.
The ASE test specification calls this content area “General Engine Diagnosis”. It carries 11 of the 55 scored questions, 20% of the test.
- Verify the complaint on a loaded road or dyno test
- Identify the engine by serial number and emission label
- Find fuel, oil, coolant, exhaust and DEF leaks
- Isolate noises and judge smoke color and opacity
- Test intake restriction, boost, back pressure and crankcase pressure
- Diagnose no-start, hard start, low power and rough running
- Check coolant condition, oil analysis results and DEF quality
- Read DTCs and calibrations, and spot tampered parts
04What the questions turn on
Boost needs fuel and load
Boost comes from exhaust energy, which comes from the fuel burned. With no load the engine makes little boost, so boost is judged at rated speed and full load. Fuel pressure below minimum can cut boost while every air-side check passes.
Where each pressure is read
Intake restriction is read at the turbocharger inlet, so a cracked charge air cooler after the compressor cannot raise it. Back pressure at the turbocharger outlet is set by everything downstream, such as a plugged muffler or loaded DPF, and it raises exhaust temperature.
What oil analysis shows
Sodium and potassium up with glycol found confirm coolant in the oil. Fuel dilution lowers viscosity, and a coolant-to-oil cooler cannot be its source. High silicon with rising wear metals and an intact element point to dirt entering through a leak after the filter.
Rule out the simple cause
A DEF sample reading inside its range on a refractometer shows the fluid is good and the quality sensor is wrong. High crankcase pressure on a closed ventilation system calls for checking the CCV filter or separator before the rings are blamed.
05The other content areas
The T2 test has eight content areas. Each has its own page of free questions:
The ASE T2 Diesel Engines practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.
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