A tractor that idles for most of each night drips a black, oily liquid from its exhaust joints and puffs blue-white smoke for a minute when it is first driven after a long idle; the smoke clears under load. Oil consumption, crankcase pressure and coolant level are all normal. Which of these is the cause?

Unburned fuel and oil from long idling

Worn turbocharger shaft seals leaking oil

Worn piston rings and cylinder liners

Coolant leaking into one or more cylinders

The scan tool shows a DPF's differential pressure, the pressure drop across the filter. Why is the reading judged only at the engine speed and load the manufacturer specifies for the check?

The drop rises and falls with exhaust flow

The ECM zeroes the sensor at each speed change

The sensor works only when the exhaust is hot

Soot burns off at idle and lowers the reading

During an overhaul of a diesel engine with wet cylinder liners, the coolant side of several liners shows clusters of small, deep pits, heaviest on the sides the pistons thrust against and in line with piston travel. What forms this kind of pitting?

Vapor bubbles collapsing on the vibrating liner

Acid from combustion gas leaking into coolant

Grit in the coolant wearing away the liner

General rusting from coolant with too much water

On a diesel engine's full-flow oil filter circuit, what does the filter bypass valve do?

Lets oil reach the bearings past a plugged filter

Returns excess pump output to the oil pan

Routes oil around the oil cooler when the oil is cold

Holds oil in the filter while the engine is stopped

Inlet air restriction on a turbocharged diesel truck is to be measured with a water manometer at the manufacturer's test speed and load. Where is the manometer connected?

Between the air cleaner and the compressor inlet

In the intake manifold, after the charge air cooler

Between the compressor outlet and the cooler inlet

At the intake hood, ahead of the air cleaner element

A common rail engine lacks power. Under load, actual rail pressure stays far below desired, and fuel flows steadily from the drain line of the rail's pressure limiting valve, a line the manufacturer says carries no flow in normal operation. Which of these could be the cause?

A limiting valve leaking past its seat

A secondary fuel filter restricted by dirt

A high-pressure pump worn internally

An injector leaking heavily to its return

When a high-pressure injection line is installed, the service information says to start the nuts at both ends by hand before either one is tightened. What is the reason?

So both cone ends meet their seats squarely

So the line can grow in length as it warms

So the cone ends can be pressed into new seats

So fuel can bleed air out of the line first

A fleet wants its trucks' electronic engine protection systems to shut the engine down, instead of only warning the driver, when oil pressure falls to a critical level. How is this done?

Reprogram the ECM's engine protection parameter

Install an oil pressure sensor with a wider range

Lower the ECM's low oil pressure warning threshold

Clear the fault history so the ECM relearns it

Many heavy-duty truck alternators have a remote sense terminal wired by a light-gauge lead to the batteries or to a main power junction near them. What does this circuit do?

Lets the regulator read voltage at the batteries

Carries part of the alternator's output to the batteries

Sends the alternator's speed signal to the tachometer

Switches the regulator on when the key is turned on

10 Free ASE T2 Diesel Engines Practice Questions, Explained

Ten ASE T2 Diesel Engines questions in the ASE format: four options, one best answer. They are free to use, print and share, and there is nothing to sign up for on this page.

01How to use these

The questions come from the ToolboxPrep T2 bank and are spread across the test's content areas in the proportion the ASE test specification gives them: A (General Engine Diagnosis), B (Cylinder Head and Valve Train Diagnosis and Repair), C (Engine Block Diagnosis and Repair), D (Lubrication and Cooling Systems Diagnosis and Repair), E (Air Induction and Exhaust Systems Diagnosis and Repair), F (Fuel System Diagnosis and Repair), G (Starting and Charging System Diagnosis and Repair), H (Engine Brakes). Answer each one before opening the explanation. Every explanation covers all four options, because knowing why the wrong answers are wrong is most of the skill.

Pace. The T2 test gives you 90 minutes for 65 questions (55 scored, 10 unscored), about 1 min 23 s a question. Try these at that pace.
Print. The printed version shows the questions and the answer key without the explanations, so it works as a handout.

02The questions

Diagnosis · General Engine Diagnosis

A tractor that idles for most of each night drips a black, oily liquid from its exhaust joints and puffs blue-white smoke for a minute when it is first driven after a long idle; the smoke clears under load. Oil consumption, crankcase pressure and coolant level are all normal. Which of these is the cause?
1. Unburned fuel and oil from long idling
2. Worn turbocharger shaft seals leaking oil
3. Worn piston rings and cylinder liners
4. Coolant leaking into one or more cylinders
Show the answer

A. Correct. At long, light-load idle the cylinders run cool, so some fuel and lube oil pass through unburned and collect in the exhaust, dripping from the joints as a black, oily liquid and smoking off when the engine is next loaded. Normal oil use and crankcase pressure rule out a mechanical oil leak; cutting idle time prevents it.

Why not the others

B. Leaking turbocharger seals would raise oil consumption steadily and leave oil in the intake or exhaust ducts. Oil consumption is normal here.

C. Worn rings and liners raise crankcase pressure (blowby) and oil consumption, and both are normal here.

D. Coolant entering a cylinder lowers the coolant level and gives white, sweet-smelling smoke. The coolant level is normal and the liquid is black and oily.

ID T2-A-001 · Task T2-A-6 (ASE task list)
Recall · General Engine Diagnosis

The scan tool shows a DPF's differential pressure, the pressure drop across the filter. Why is the reading judged only at the engine speed and load the manufacturer specifies for the check?
1. The ECM zeroes the sensor at each speed change
2. The sensor works only when the exhaust is hot
3. Soot burns off at idle and lowers the reading
4. The drop rises and falls with exhaust flow
Show the answer

D. Correct. The pressure drop across a filter depends on how much gas is being pushed through it as well as on how loaded it is, so the same filter reads low at idle and high at full load. Only a reading at the specified speed and load can be compared with the limit to judge soot and ash loading.

Why not the others

A. The ECM does not re-zero the sensor with each speed change; the reading really does change with exhaust flow, which is why the test condition is specified.

B. The differential pressure sensor reads whenever the engine runs; exhaust temperature does not switch it on. The reading changes with exhaust flow, so the flow condition has to be fixed.

C. Exhaust at idle is too cool to burn soot in the filter. The reading is low at idle because little gas flows through the filter.

ID T2-A-021 · Task T2-A-10 (ASE task list)
Recall · Cylinder Head and Valve Train Diagnosis and Repair

An inline six-cylinder diesel fires 1-5-3-6-2-4. To set valve clearance, a technician bars the engine over until the timing mark reads TDC with cylinder 6's valves rocking, its exhaust valve closing as its intake valve begins to open. Which cylinder's piston is now at TDC on its compression stroke?
1. Cylinder 1
2. Cylinder 2
3. Cylinder 3
4. Cylinder 6
Show the answer

A. Correct. In an inline six the pistons move in pairs (1 and 6, 2 and 5, 3 and 4), and the two cylinders of a pair are 360 degrees apart in the firing order. With cylinder 6 at TDC on valve overlap, its partner, cylinder 1, is at TDC on compression with both valves closed, so its clearances can be set.

Why not the others

B. Cylinder 2 fires next after cylinder 6, but it is not at TDC: it reaches its next top center 120 degrees of crank rotation from now, so its piston is partway up on its exhaust stroke. Cylinder 1, the partner of the rocking cylinder 6, is the one at TDC on compression.

C. Cylinder 3 fires just before cylinder 6 in the order, which puts its piston 120 degrees past top center, on its way down on the intake stroke. The cylinder at TDC on compression is cylinder 1, the partner of the rocking cylinder 6.

D. Cylinder 6 is at TDC, but at the end of its exhaust stroke: rocking valves mean both are slightly open at overlap, so its clearances cannot be set now. Its partner, cylinder 1, is the one at TDC on compression with both valves closed.

ID T2-B-001 · Task T2-B-10 (ASE task list)
Recall · Engine Block Diagnosis and Repair

During an overhaul of a diesel engine with wet cylinder liners, the coolant side of several liners shows clusters of small, deep pits, heaviest on the sides the pistons thrust against and in line with piston travel. What forms this kind of pitting?
1. Vapor bubbles collapsing on the vibrating liner
2. Acid from combustion gas leaking into coolant
3. Grit in the coolant wearing away the liner
4. General rusting from coolant with too much water
Show the answer

A. Correct. Each time a piston thrusts against the liner, the thin liner wall vibrates; as it moves away from the coolant, the pressure there drops below the coolant's vapor pressure and bubbles form, then collapse hard enough to blast out tiny bits of metal. That is cavitation, and it is why the pits line up with the thrust sides. Keeping the coolant's liner-protecting additive at the manufacturer's level, with the system full and pressurized, guards against it.

Why not the others

B. Acid in the coolant from combustion gas would attack the metal it touches throughout the cooling system, not only the thrust sides of the liners in line with piston travel. Pits clustered on the thrust sides come from cavitation: vapor bubbles collapsing against the vibrating liner wall.

C. Grit carried in the coolant wears smooth, scoured areas where the flow strikes hardest, such as near the coolant inlet, and has nothing to do with where the pistons thrust. Deep pits lined up with the thrust sides are cavitation damage from bubbles collapsing against the vibrating wall.

D. Coolant mixed too weak rusts iron surfaces in general, leaving scale over all the wetted metal rather than deep pits concentrated on the thrust sides. Pitting that follows the thrust sides and piston travel is cavitation, driven by the vibration of the liner wall.

ID T2-C-001 · Task T2-C-4 (ASE task list)
Recall · Lubrication and Cooling Systems Diagnosis and Repair

On a diesel engine's full-flow oil filter circuit, what does the filter bypass valve do?
1. Returns excess pump output to the oil pan
2. Routes oil around the oil cooler when the oil is cold
3. Holds oil in the filter while the engine is stopped
4. Lets oil reach the bearings past a plugged filter
Show the answer

D. Correct. When the filter is plugged, or cold, thick oil cannot pass the element fast enough, the bypass valve opens so the bearings still get oil, though unfiltered. That is why a skipped filter change can let dirty oil circulate with no warning drop in oil pressure.

Why not the others

A. That is the job of the pressure regulating (relief) valve, which limits system pressure. The filter bypass valve opens only when the pressure drop across the filter is too high.

B. That is the oil cooler bypass valve or oil thermostat. The filter bypass valve answers to filter restriction, keeping oil moving to the bearings when the element cannot pass it.

C. That is the anti-drainback valve, which keeps the filter full for a quick pressure rise at startup. The bypass valve opens when the filter is restricted.

ID T2-D-004 · Task T2-D-3 (ASE task list)
Recall · Air Induction and Exhaust Systems Diagnosis and Repair

Inlet air restriction on a turbocharged diesel truck is to be measured with a water manometer at the manufacturer's test speed and load. Where is the manometer connected?
1. In the intake manifold, after the charge air cooler
2. Between the compressor outlet and the cooler inlet
3. Between the air cleaner and the compressor inlet
4. At the intake hood, ahead of the air cleaner element
Show the answer

C. Correct. Inlet restriction is the vacuum the engine pulls to draw air through the precleaner, element and inlet piping, and it is greatest at the compressor inlet. A tap on the clean-air side between the air cleaner and the turbocharger sees the whole drop, which is compared with the manufacturer's limit.

Why not the others

A. The intake manifold of a turbocharged diesel is under boost under load, so a gauge there reads boost minus the cooler's pressure drop. Inlet restriction is measured before the compressor, where the engine draws air through the air cleaner.

B. After the compressor the air is under boost pressure, so a gauge there reads boost, not the vacuum caused by the air cleaner. Restriction is read upstream of the compressor, on the clean side of the air cleaner.

D. Ahead of the air cleaner the air is still close to atmospheric pressure, so a gauge there misses the drop across the element. The tap goes after the air cleaner, between its outlet and the compressor inlet.

ID T2-E-003 · Task T2-E-1 (ASE task list)
Diagnosis · Fuel System Diagnosis and Repair

A common rail engine lacks power. Under load, actual rail pressure stays far below desired, and fuel flows steadily from the drain line of the rail's pressure limiting valve, a line the manufacturer says carries no flow in normal operation. Which of these could be the cause?
1. A limiting valve leaking past its seat
2. A secondary fuel filter restricted by dirt
3. A high-pressure pump worn internally
4. An injector leaking heavily to its return
Show the answer

A. Correct. The pressure limiting valve should stay shut until rail pressure passes its maximum, so steady flow from its drain line means rail fuel is escaping through it. That bleed-off keeps the pump from holding the pressure the ECM wants; the valve is replaced as the service information directs, and the reason it opened is checked if the system can over-pressurize.

Why not the others

B. A restricted filter starves the high-pressure pump and can keep rail pressure low, but it cannot send fuel out of the limiting valve's drain line. Flow in a line that should be dry points to the valve itself.

C. A worn pump delivers too little fuel to hold rail pressure, but its internal leakage returns inside the pump, not through the rail's limiting valve. Steady flow from that valve's drain shows the rail is losing fuel through it.

D. Injector leakage leaves through the injector return lines, not through the limiting valve's drain. With flow showing in a line that should carry none, the limiting valve is where rail fuel is escaping.

ID T2-F-003 · Task T2-F-6 (ASE task list)
Recall · Fuel System Diagnosis and Repair

When a high-pressure injection line is installed, the service information says to start the nuts at both ends by hand before either one is tightened. What is the reason?
1. So the line can grow in length as it warms
2. So the cone ends can be pressed into new seats
3. So fuel can bleed air out of the line first
4. So both cone ends meet their seats squarely
Show the answer

D. Correct. Starting both nuts by hand lets the line settle into its natural position, so each cone end sits squarely in its seat with no side load. A line forced into place by tightening one end first can leak at the other end, damage a seat or crack later from the built-in stress and vibration; both nuts are then torqued to the manufacturer's specification.

Why not the others

A. The thermal growth of a short steel line is tiny and is not taken up at the nuts. Hand-starting both nuts lets the cone ends align with their seats so the line goes in without strain.

B. The cone ends and seats are precision surfaces meant to seal as made; forcing them to reshape damages them and causes leaks. Starting both nuts by hand is about aligning the cones squarely in their seats before tightening.

C. Air is bled as the service information directs, usually from the low-pressure side; that is not the reason for starting both nuts by hand. That step makes sure the line is not strained when the nuts are tightened.

ID T2-F-019 · Task T2-F-5 (ASE task list)
Recall · Fuel System Diagnosis and Repair

A fleet wants its trucks' electronic engine protection systems to shut the engine down, instead of only warning the driver, when oil pressure falls to a critical level. How is this done?
1. Reprogram the ECM's engine protection parameter
2. Install an oil pressure sensor with a wider range
3. Lower the ECM's low oil pressure warning threshold
4. Clear the fault history so the ECM relearns it
Show the answer

A. Correct. On electronically controlled engines the protection system's response to a critical reading (warning only, derate or shutdown) is a programmable parameter, changed with the manufacturer's service software. Record the change and confirm the new setting afterward.

Why not the others

B. The sensor only reports pressure; a different range would not change what the ECM does with a low reading and could make the readings wrong. The response is chosen in the ECM's programming.

C. Changing the threshold changes when the system reacts, not how it reacts; the engine would still only warn the driver. The response itself, warning, derate or shutdown, is a programmed setting in the ECM.

D. Clearing faults erases the record of past events; it does not change how the protection system responds. The shutdown feature is turned on by changing the ECM's protection parameter with the service software.

ID T2-F-038 · Task T2-F-10 (ASE task list)
Recall · Starting and Charging System Diagnosis and Repair

Many heavy-duty truck alternators have a remote sense terminal wired by a light-gauge lead to the batteries or to a main power junction near them. What does this circuit do?
1. Carries part of the alternator's output to the batteries
2. Lets the regulator read voltage at the batteries
3. Sends the alternator's speed signal to the tachometer
4. Switches the regulator on when the key is turned on
Show the answer

B. Correct. The regulator reads system voltage through the sense lead at the batteries instead of at its own output terminal, so it raises output enough to make up for the voltage lost in a long output cable. The batteries then charge at the regulator's set voltage.

Why not the others

A. The sense lead carries only a tiny measuring current, which is why it can be a light-gauge wire; all charging current goes through the output cable. The lead's job is to report the voltage at the batteries to the regulator.

C. A tachometer signal comes from a stator tap terminal that puts out an AC signal proportional to alternator speed. The remote sense lead instead gives the regulator the voltage at the batteries.

D. Turning the regulator on at key-on is the job of an ignition or excitation terminal where an alternator has one. The remote sense lead gives the regulator the voltage at the batteries so it can make up for output-cable drop.

ID T2-G-002 · Task T2-G-6 (ASE task list)

03Answer key

Question	Answer	Content area
Q1	A	General Engine Diagnosis
Q2	D	General Engine Diagnosis
Q3	A	Cylinder Head and Valve Train Diagnosis and Repair
Q4	A	Engine Block Diagnosis and Repair
Q5	D	Lubrication and Cooling Systems Diagnosis and Repair
Q6	C	Air Induction and Exhaust Systems Diagnosis and Repair
Q7	A	Fuel System Diagnosis and Repair
Q8	D	Fuel System Diagnosis and Repair
Q9	A	Fuel System Diagnosis and Repair
Q10	B	Starting and Charging System Diagnosis and Repair

04Questions by content area

Working on one part of the T2 test? Each content area has its own page with five more free questions.

05More free questions

The T2 study guide covers each content area and how to study for it, and the ASE T2 Diesel Engines practice test page describes the full T2 question bank. The same free format is available for the other 15 tests.

How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.

ToolboxPrep is an independent study site, not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original, written from ASE’s published test specifications and task lists and other public sources. They are not actual ASE test questions and not recalled or “brain dump” questions. ASE is a trademark of its owner, and we never use the ASE logo. Standards and service information are cited, not reproduced.