Five ASE L1 Advanced Engine Performance Specialist practice test questions, answers included.

1. Recall · General Powertrain Diagnosis

   A replacement catalytic converter is listed by its maker according to the emission test group the vehicle was certified to. Where on the vehicle does the technician find the test group identification?

   1. On the tire and loading placard in the door opening
   2. In the tenth character of the VIN
   3. On the emission control label under the hood
   4. In the calibration ID read with a scan tool
   Show the answer

   C. Correct. Federal rules require a permanent Vehicle Emission Control Information label in the engine compartment that shows the engine displacement, the test group and the evaporative/refueling family. Reading it first makes sure the replacement part matches how that vehicle was certified.

   Why not the others

   A. The door-opening placard gives tire sizes, inflation pressures and load limits. The test group is printed on the Vehicle Emission Control Information label in the engine compartment.

   B. The tenth VIN character gives the model year, not the emission test group. Vehicles of the same year can be certified to different test groups, which is why the underhood emission control label is read.

   D. The calibration ID identifies the PCM software version, which matters for reprogramming. It is not the emission test group; that is printed on the emission control label under the hood.

2. Spec reading · Computerized Powertrain Controls Diagnosis (including OBD II)

   On a vehicle with the MIL off and no confirmed DTCs, the scan tool's on-board monitor test results (Mode $06) for the bank 1 catalyst show a test value of 0.84, a minimum limit of 0.00 and a maximum limit of 0.75. What does this result mean?

   1. The catalyst is 84 % efficient
   2. The catalyst passed by a 0.09 margin
   3. The catalyst monitor has not yet run
   4. The catalyst failed its latest test
   Show the answer

   D. Correct. Mode $06 reports each monitor test's latest result with the limits it is judged against, and a value outside the minimum-to-maximum range is a failed test: 0.84 is above the 0.75 maximum. A failing result can show here before a confirmed DTC sets, which makes Mode $06 useful for catching a weakening catalyst or checking a repair.

   Why not the others

   A. The test value is a number in the manufacturer's own scaling for that test, not an efficiency percentage. What matters is how it compares with the limits: 0.84 is above the 0.75 maximum, so it fails.

   B. The 0.09 difference (0.84 - 0.75) is how far the value is beyond the maximum limit, not a passing margin. A result passes only when it falls between the minimum and maximum limits.

   C. After DTCs are cleared, a monitor that has not yet completed reports a value that does not indicate a failure, so a value outside its limits shows the test has run. This one ran and landed above the maximum.

3. EXCEPT · Computerized Powertrain Controls Diagnosis (including OBD II)

   During an inspection for modified or tampered engine-control parts, any of these would show the system has been changed from its original certified setup EXCEPT:

   1. a resistor spliced into the ECT sensor signal wire.
   2. an add-on module wired between the MAF sensor and PCM.
   3. an EGR passage sealed with a block-off plate.
   4. a PCM calibration installed under a factory bulletin.
   Show the answer

   D. Correct. A calibration released by the vehicle manufacturer and installed under its bulletin is part of the manufacturer's own certified setup, and its calibration ID appears in the manufacturer's service information. The other three alter a control input or disable an emission control, which is tampering.

   Why not the others

   A. A resistor added to the ECT signal makes the PCM see a different, usually colder, engine than the real one and changes its fuel and spark; it alters a control input and is a tampering finding.

   B. A module between the MAF sensor and the PCM alters the airflow signal the PCM uses to calculate fuel and spark, so the system no longer works as certified.

   C. Blocking the EGR passage disables an emission control the PCM operates, raising NOx, and is a classic tampering finding.

4. Recall · Fuel Systems and Air Induction Systems Diagnosis

   On a gasoline direct injection (GDI) engine, the ECM opens each injector with a brief pulse at a voltage far above battery voltage, then holds it open at a much lower current. Why is the high opening voltage used?

   1. To burn carbon deposits off the nozzle tip
   2. To snap it open against high rail pressure
   3. To make up for voltage lost in the harness
   4. To test the winding for a short each pulse
   Show the answer

   B. Correct. A GDI injector must open against rail pressure many times higher than a port injector sees, within a short window of the engine cycle. The boosted voltage builds current fast so the needle lifts quickly and repeatably; once it is open, far less current holds it, which keeps the injector and driver from overheating.

   Why not the others

   A. The opening pulse lasts a fraction of a millisecond and works by magnetism, not heat, so it does nothing to tip deposits. The high voltage builds current quickly so the injector opens fast against high rail pressure.

   C. Harness voltage drop at injector current is small and would never call for a voltage far above battery voltage. The boost builds opening current quickly against the high rail pressure of direct injection.

   D. Checking a winding does not need a voltage above battery voltage. The raised voltage is there to build current fast so the injector opens quickly against high rail pressure.

5. Recall · Emission Control Systems Diagnosis

   A warm engine is running rich because of a fuel control fault, and its three-way catalytic converter now gives off a rotten-egg odor. Which gas is the converter releasing?

   1. Sulfur dioxide (SO2)
   2. Hydrogen sulfide (H2S)
   3. Carbon monoxide (CO)
   4. Nitrogen dioxide (NO2)
   Show the answer

   B. Correct. Sulfur from the fuel is stored on the catalyst while the exhaust carries oxygen; when the exhaust runs rich, that sulfur is reduced to hydrogen sulfide, which smells like rotten eggs. Repairing the rich condition stops the odor, so the fuel control fault is diagnosed before the converter is blamed.

   Why not the others

   A. SO2 is what fuel sulfur forms when oxygen is available, and it has a sharp, choking smell rather than a rotten-egg odor. In rich exhaust the converter turns its stored sulfur into hydrogen sulfide instead.

   C. Rich exhaust does carry more CO, but carbon monoxide has no odor at all, which is what makes it so dangerous. The rotten-egg smell is hydrogen sulfide made from fuel sulfur.

   D. NO2 forms where oxygen is plentiful, and a converter fed rich exhaust reduces nitrogen oxides rather than making more. The rotten-egg odor comes from hydrogen sulfide.

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