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Quiz Session - Attempts With Random Questions

ASE L2 Exam Questions

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1.

Technician A states that some engines use glow plug systems to aid in starting and to limit exhaust smoke when engines are cold. Technician B states that some engines have a pre-heater that gets turned on by the ECM when the engine is cold.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Some engines use air inlet pre-heaters to heat the air entering the engine. Other engines use glow plug systems for the same purposes, while some have both systems installed.

The pre-heater is turned on by the ECM when the engine gets cold. Both of these systems ensure faster starting times and limited exhaust smoke during colder temperatures.

2.

Using the composite vehicle on the ASE website, answer the following question:

Technician A states that the ignition switch supplies 12 V to the ECM when the power relay is in the ON position. Technician B states that the ignition switch supplies 12 V to the ECM when in the START position.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Technician A is correct because the ignition switch supplies 12 V to the ECM when the power relay is in the ON position. During this time, the ignition switch commands the ECM and additional modules to start communication.

Technician B is also correct because the ignition switch supplies 12 V to the ECM when in the START position. During this time, the ignition switch requests starter operation.

3.

Using the composite vehicle on the ASE website, answer the following question:

How many ohms is the resistor in the VGT actuator?

  • 120 ohms

  • 100 ohms

  • 60 ohms

  • 240 ohms

Correct answer: 120 ohms

There is a 120-ohm terminating resistor in the VGT actuator used for diagnostics.

The VGT actuator is connected to the ECM at terminals 411 and 412. It contains four wires: data high, data low, 12 V, and ground.

4.

Using the composite vehicle on the ASE website, answer the following question:

How many temperature sensors are part of the aftertreatment temperature sensor module?

  • Four

  • Six

  • Five

  • Three

Correct answer: Four

The aftertreatment temperature sensor module consists of four individual temperature sensors located within the exhaust stream. The individual sensor probes include:

  • The DOC inlet temperature sensor (located before the DOC)
  • The DPF inlet temperature sensor (located after the DOC)
  • The DPF outlet temperature sensor (located after the diesel particulate filter)
  • The SCR outlet temperature sensor (located after the selective catalytic reduction unit)

The aftertreatment temperature sensor module communicates on the J1939 private CAN to the ECM. This information is used to monitor the exhaust aftertreatment efficiency and performance.

5.

How many wires does a resistor have?

  • Two or three

  • One or two

  • Two

  • Three

Correct answer: Two or three

Resistors contain either a two-wire or three-wire configuration. Temperature sensors are commonly configured as a two-wire resistor, while the throttle position sensor (TPS) is usually a three-wire resistor.

Resistors need to restrict the current flow. However, a component is only considered a resistor when placed under a load. If it's not part of a complete circuit, it cannot perform its necessary function.

6.

Technician A states that slow acceleration can be caused by a restricted diesel oxidation catalyst (DOC). Technician B states the cause of slow acceleration may be due to a restricted air cleaner.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Both technicians are correct. Any component that's restricting airflow through the engine can slow acceleration. Reduced airflow through the air intake or exhaust can be to blame. 

Slow acceleration can come from a restricted diesel oxidation catalyst (DOC) or a restricted air cleaner.

7.

Using the composite vehicle on the ASE website, answer the following question:

How many different modes of operation does the DEF lamp have?

  • Three

  • Two

  • Four

  • Five

Correct answer: Three

The DEF lamp has three modes of operation: on, off, and flashing.

With the DEF lamp off, the level is considered normal and there's no action needed. When the DEF lamp is on, it means that the level is low. Once it begins flashing, the DEF level is at a critical level.

8.

Using the composite vehicle on the ASE website, answer the following question:

How many modes of operation does the high exhaust temperature lamp have?

  • Three

  • Two

  • Four

  • Five

Correct answer: Three

The high exhaust temperature system temperature lamp has three different modes of operation: on, off, and flashing.

The high exhaust system temperature lamp (HEST) comes on when it receives a signal from the ECM that the exhaust outlet temperature has reached 850 °F (454 °C) or greater with the vehicle traveling at speeds under 5 MPH.

9.

Using the composite vehicle on the ASE website, answer the following question:

Technician A states that the DEF pressure sensor voltage range is the same as the AFT fuel pressure sensor voltage range. Technician B states that the DEF pressure sensor PSI range is the same as the engine oil pressure sensor.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

The DEF pressure sensor voltage varies between 0.5 and 4.5, while the pressure varies between 0 and 200 PSI. As pressure increases, voltage increases.

These are the same ranges shared by the AFT fuel pressure sensor and engine oil pressure sensor, making both technicians correct. These values are also shared by the exhaust back pressure sensor and the fuel delivery pressure sensor.

10.

Technician A states that DOCs reduce carbon monoxide. Technician B states that DOCs reduce hydrocarbons.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Catalysts react with the exhaust gases to convert nitrogen oxide into nitrogen dioxide and oxide-absorbed hydrocarbons. DOCs reduce carbon monoxide, hydrocarbons, and odor-causing compounds.

The main function of DOCs is to start regeneration events by converting the exhaust gases into heat.

11.

Using the composite vehicle on the ASE website, answer the following question:

What should the voltage show at APP 1 sensor on a scan tool with the pedal fully released?

  • 1.50 volts

  • 3.50 volts

  • 2.50 volts

  • 4.50 volts

Correct answer: 1.50 volts

The APP 1 sensor voltage varies between 1.50 and 4.50. With the pedal at rest, the app sensor should read 1.50 volts from the scan tool. At the same time, APP 2 sensor would read 0.50 volts.

The sensor should read 4.50 volts when fully depressed while monitoring the scan tool, while APP 2 sensor would read 3.50 volts.

12.

Using the composite vehicle on the ASE website, answer the following question:

What is the coil resistance specification for the DEF supply pump relay coil?

  • 86-94 ohms

  • 80-85 ohms

  • 76-89 ohms

  • 92-102 ohms

Correct answer: 86-94 ohms

The DEF supply pump relay provides battery voltage to the DEF supply pump. The coil resistance specification is  90 ± 4 Ω, so it could be anywhere from 86 to 94 ohms.

The DEF supply pump relay gets energized by the ECM and gives battery voltage (B+) to the DEF supply pump.

13.

Using the composite vehicle on the ASE website, answer the following question:

Technician A states that the fuel temperature sensor is located on the primary fuel filter housing. Technician B states that the fuel temperature sensor is located on the secondary fuel filter housing.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician B

The fuel temperature sensor is located on the secondary fuel filter housing and is used for fuel management. The ECM relies on this signal for fuel management. It is needed to compensate for fuel temperatures and to provide engine protection.

14.

Using the composite vehicle on the ASE website, answer the following question:

How many wires does a diesel particulate filter regeneration switch have?

  • Two

  • Three

  • Four

  • Five

Correct answer: Two

The diesel particulate filter regeneration switch is a two-wire, normally open momentary switch. It is wired to the BCM.

When this switch is pressed (closed) and released, it sends a request to the ECM that enables a parked DPF regeneration.

15.

Using the composite vehicle on the ASE website, answer the following question:

Technician A states that the crankshaft position is used for injector timing. Technician B states that the crankshaft position is used for fuel control.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

The ECM uses a crankshaft position for fuel control and injector timing. If there is a fault in the circuit, a DTC will set.

The CKP is found in the engine rear flywheel housing. It faces the trigger/tone wheel that's mounted on the crankshaft. The signal generated by the CKP increases in conjunction with the crankshaft's speed.

16.

Technician A states that many diesels have a fuel pressure gauge mounted to the engine. Technician B states that the pressure gauges mounted to the engine should be used for diagnostics.

Who is correct?

  • Technician A

  • Technician B

  • Both A and B

  • Neither A nor B

Correct answer: Technician A

Many diesel engines have fuel pressure gauges mounted to the engine. These gauges are notorious for being inaccurate and should not be used for diagnostics.

A fuel pressure gauge tool that has been proven to be accurate should be used instead.

17.

Technician A states that leaking injector tube seals can cause steam from the exhaust stream. Technician B states that steam from the exhaust indicates water has entered the combustion process.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Both technicians are correct. White steam is indicative of water entering the combustion process. Faulty injector tube seals can be to blame, as water can enter the combustion process through the damaged seals. If an injector tube continues to leak coolant, the engine may endure permanent damage or experience hydrostatic lock.

18.

Technician A believes that freeze frame data stores sensor readings when a DTC is set. Technician B states that the operating condition of most engine actuators is recorded when a DTC is set.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Both technicians are correct. Freeze frame data is stored by the ECM when a diagnostic trouble code (DTC) is set.

The freeze frame data includes sensor readings, the operating condition of most engine actuators, the ECM time, and engine parameters at the time of the DTC being set. This data allows technicians to see the conditions at the time of the malfunction.

19.

Technician A states that fuel pressure should be checked at idle. Technician B states that fuel pressure should be checked at full-rated speed.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Fuel pressure should be checked at both idle and full-rated speed, making both technicians correct. If only one is checked, the technician can go down the wrong path when diagnosing the vehicle.

If fuel pressure is too high, the pump pressure relief may be open, creating low volume. If the fuel pressure rises too rapidly, clogged fuel return components may be the culprit.

20.

Using the composite vehicle on the ASE website, answer the following question:

Technician A states that if fuse 41 were blown, it would cause a DEF DTC to set. Technician B states that if fuse 41 were blown, it would cause a NOx sensor module code.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Fuse 41 sends power to the DEF quality sensor along with all the NOx sensors. If this fuse were blown, DTCs in both systems would set, making both technicians correct.

The aftertreatment temperature sensor module and the PM sensor module also run on fuse 41.

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