Five ASE T2 Diesel Engines practice test questions, answers included.

1. Recall · General Engine Diagnosis

   A technician suspects coolant is getting into a truck engine's oil and sends an oil sample for analysis. Which of these lab results would confirm it?

   1. Silicon up, along with iron and chromium
   2. Sodium and potassium up, glycol found
   3. Soot above the lab's limit for the oil
   4. Lead and tin above the earlier samples
   Show the answer

   B. Correct. Many coolants carry sodium- and potassium-based inhibitors, and glycol is the coolant itself, so a rise in sodium and potassium together with glycol confirms coolant in the oil. Compare with earlier samples from the same engine, since some oils carry sodium additives, then find the leak, such as the oil cooler or a head gasket.

   Why not the others

   A. Silicon with rising iron and chromium points to dirt getting into the engine and wearing the liners and rings, not to coolant.

   C. High soot comes from combustion, such as overfueling or restricted air, and says nothing about coolant in the oil.

   D. Lead and tin come from bearing overlays, so a rise points to bearing wear; on its own it does not confirm coolant in the oil.

   ID T2-A-002 · Task T2-A-15 (ASE task list)

2. Recall · Lubrication and Cooling Systems Diagnosis and Repair

   On a heavy-duty diesel, the coolant filter sits in a small loop that carries part of the coolant flow beside the main circuit, with a shutoff valve on each of its lines. After an SCA-charged filter is installed at a PM, both valves are left closed. What is the result?

   1. The coolant gets no filtering or SCA
   2. The engine overheats from lost flow
   3. The coolant is overdosed with SCA
   4. The filter element plugs up with debris
   Show the answer

   A. Correct. With both valves closed no coolant passes through the filter, so the element traps no debris and the supplemental coolant additive (SCA) in the charged filter never dissolves into the system, while the coolant's additive keeps being used up. The valves are opened once the new filter is on, and the head checked for leaks.

   Why not the others

   B. The filter loop carries only a small part of the flow beside the main circuit, so closing it does not cut flow through the engine and radiator. What is lost is the filtering and the SCA the charged filter would release.

   C. A charged filter releases its SCA only into coolant that flows through it. With the valves closed nothing flows, so the coolant gets no SCA from it at all, the opposite of an overdose.

   D. An element collects only the debris that coolant carries into it. With both valves closed no coolant reaches the element, so it stays clean while the coolant goes unfiltered and undosed.

   ID T2-D-001 · Task T2-D-11 (ASE task list)

3. Recall · Air Induction and Exhaust Systems Diagnosis and Repair

   On a diesel engine with a variable-geometry turbocharger (VGT), how does the engine control module (ECM) raise boost at low engine speed?

   1. It opens the turbine vanes fully to let more exhaust reach the wheel
   2. It narrows the turbine vanes to speed the exhaust onto the wheel
   3. It opens a wastegate so exhaust bypasses the turbine wheel
   4. It recirculates compressed air from the outlet back to the inlet
   Show the answer

   B. Correct. Closing the vanes narrows the passage into the turbine, so the limited exhaust flow at low engine speed strikes the wheel faster and spins it harder, raising boost. As engine speed and exhaust flow rise, the ECM opens the vanes to hold boost at its target and keep back pressure down.

   Why not the others

   A. This is the reverse. Wide-open vanes give the slow exhaust flow at low engine speed a large passage, so it reaches the wheel slowly and boost stays low; the ECM opens the vanes at high flow and closes them to build boost at low speed.

   C. A wastegate routes exhaust around the turbine, which lowers turbine speed and limits boost; it is used on fixed-geometry turbochargers. A VGT raises boost at low speed by narrowing its vanes, not by bypassing exhaust.

   D. Returning compressed air to the compressor inlet bleeds off boost; it does not build it. At low speed the VGT builds boost on the turbine side, by narrowing its vanes so the exhaust drives the wheel faster.

   ID T2-E-002 · Task T2-E-2 (ASE task list)

4. Recall · Fuel System Diagnosis and Repair

   A fuel/water separator has a water-in-fuel (WIF) sensor with two metal probes in the bottom of its bowl. How does the sensor tell water from fuel?

   1. Water floats up and lifts a magnet to the probes
   2. Water lets current pass between the probes
   3. Water changes the temperature at the probes
   4. Water blocks light passing between the probes
   Show the answer

   B. Correct. Diesel fuel is a very poor conductor of electricity, while water carries current. Water is heavier than diesel fuel and settles to the bottom of the bowl, and when it reaches the probes the resistance between them drops, so the module or ECM turns on the water-in-fuel warning and the bowl can be drained.

   Why not the others

   A. Water is heavier than diesel fuel, so it sinks to the bottom of the bowl instead of floating; that is why the probes and the drain valve are at the bottom. These probes sense the drop in resistance when water bridges them.

   C. The probes do not measure temperature, and water and fuel sitting in the same bowl are at about the same temperature. The sensor reads the drop in resistance when water, which conducts, reaches the probes.

   D. Bare metal probes cannot sense light. They sense conductivity: water bridging the probes lets current flow, while diesel fuel does not.

   ID T2-F-002 · Task T2-F-2 (ASE task list)

5. EXCEPT · Fuel System Diagnosis and Repair

   On a common rail engine, any of these could cause actual rail pressure to fall below desired at full load EXCEPT:

   1. an internally worn high-pressure pump.
   2. a restricted secondary fuel filter.
   3. an injector stuck closed on one cylinder.
   4. aerated fuel from a suction-side air leak.
   Show the answer

   C. Correct. An injector that never opens takes no fuel from the rail, so the pump has less to supply and rail pressure is easier to hold. It causes a dead cylinder, with misfire and rough running, not low rail pressure.

   Why not the others

   A. This could cause it. A worn pump leaks internally and cannot deliver the volume needed to hold rail pressure while the injectors are drawing the most fuel.

   B. This could cause it. The high-pressure pump can only compress the fuel it is fed, so a restricted filter starves it when demand is highest, at full load.

   D. This could cause it. Air in the fuel compresses, so the high-pressure pump delivers less fuel per stroke and cannot hold rail pressure when demand is highest, at full load.

   ID T2-F-024 · Task T2-F-6 (ASE task list)

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