ASE L2 Exam Questions

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121.

Technician A states that low fuel return rates indicate failed injectors. Technician B states that high fuel return rates indicate a restricted supply system.

Who is correct?

  • Neither A nor B

  • Technician A

  • Technician B

  • Both A and B

Correct answer: Neither A nor B

Low fuel return rates indicate a restricted supply system, making technician A incorrect. High fuel return rates indicate failed fuel injectors, making technician B incorrect.

To check the fuel return rates, the fuel return line can be placed in a graduated container while the engine runs at a specified RPM for the manufacturer's recommended time.

122.

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

Technician A states that the fuel primer pump is mechanical. Technician B states that the fuel primer pump runs for 60 seconds when the ignition is turned on.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician B

The fuel primer pump is electronic. It supplies 15-PSI fuel pressure with the key on engine off (KOEO). 

The electric fuel primer pump runs for 60 seconds when the key is turned on.

123.

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

How many accelerator pedal position (APP) sensors are there?

  • Two

  • Three

  • Four

  • Five

Correct answer: Two

The ECM of this composite vehicle is connected to two accelerator pedal position (APP) sensors. They are labeled APP 1 and APP 2.

Each APP sensor has three connections: signal, ground, and the 5-V reference.

124.

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

Technician A states that the DEF doser valve is in the decomposition reactor tube. Technician B states that the reactor tube blends the DEF with the hot gases.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

The DEF pump supplies fluid to the DEF doser valve. The DEF doser valve injects diesel exhaust fluid into the decomposition reactor tube.

Inside the reactor tube, the DEF and hot gases mix together, making both technicians correct.

125.

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

At what temperature does the high exhaust lamp illuminate?

  • 850 °F

  • 750 °F

  • 950 °F

  • 1050 °F

Correct answer: 850 °F

The high exhaust system temperature lamp illuminates when the exhaust exceeds 850 °F.  It also comes on when an active regeneration occurs.

If parked regeneration occurs, the lamp will flash.

126.

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

Technician A states that the fuel delivery pressure sensor is before the secondary filter. Technician B states that the fuel delivery pressure sensor is after the secondary filter.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician B

The fuel delivery pressure sensor monitors fuel pressure after the secondary fuel filter, making technician B correct. The sensor monitors the pressure of the fuel before it enters the high pressure pump.

The ECM uses this signal to control injection timing and fuel metering.

127.

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

Technician A states that a short between terminal 251 of the ECM and the APP sensor will not cause a DTC. Technician B states that an open at terminal 253 will cause a DTC to set.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician B

Terminal 251 is the signal circuit from the ECM. If this circuit was shorted to ground, a DTC would be set, making technician A incorrect. Terminal 253 is a 5-V reference, and a DTC would also be set if the circuit was open.

A bad connection at terminal 252 could also lead to a DTC.

128.

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

What is the pressure that the DEF supply pump supplies to the DEF doser valve?

  • 130 PSI

  • 150 PSI

  • 140 PSI

  • 125 PSI

Correct answer: 130 PSI

The DEF supply pump is supplied B+ voltage from the relay. The pump is used to supply DEF to the DEF dosser valve at a pressure of 130 PSI.

It contains both an inlet screen and an outlet filter. At key OFF, the DEF supply pump reverses rotation to clear the lines of DEF by grounding its directional control circuit.

129.

Technician A states that a scanner stores active codes. Technician B states that a scanner stores inactive codes.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Scanners typically reveal active codes, making technician A correct. Technician B is also correct because the inactive code data will be stored.

Technicians should always examine the operating hours from the last code set to help determine what's wrong.

130.

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

While monitoring the intake manifold temperature sensor with a scan tool, what should the voltage be if the temperature is at 32 °F?

  • 3.60 volts

  • 4.50 volts

  • 0.75 volts

  • .50 volts

Correct answer: 3.60 volts

The voltage varies between 0.5 and 4.50 volts, and the temperature varies between 280 °F and -40 °F.

When the temperature is at 32 °F, the corresponding voltage reading should be 3.60 volts.

131.

After repairing a fuel system problem, all of the following should be performed by the technician, except:

  • Fill up the tank with clean diesel fuel

  • Take the vehicle for a test drive

  • Scan for trouble codes

  • Review the live data stream

Correct answer: Fill up the tank with clean diesel fuel

There's no need to fill up the tank after a repair. Yet, it is important to take the vehicle for a test drive and expose it to multiple loads. If the original operating conditions can be duplicated, that's what should be used to check the repair. Additionally, connecting a scan tool to look for codes and to review the live data stream are both necessary steps to ensure the problem is resolved.

132.

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

What is the PPM range of the NOx sensor modules, in and out?

  • 0-3000 ppm

  • 0-2000 ppm

  • 0-1000 ppm

  • 0-4000 ppm

Correct answer: 0-3000 PPM

The NOx sensors monitor oxides of nitrogen in the exhaust stream with a range of 0-3000 PPM. There's an IN and an OUT sensor.

The NOx IN sensor module is found before the DOC, while the NOx OUT sensor module is found after the SCR catalyst.

133.

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

How many of the terminating resistors used on the private network CAN system are found at the end of the backbone harness?

  • One

  • Two

  • Three

  • Four

Correct answer: One

There are two 120-ohm terminating resistors used on the private network CAN system. One is located at the end of the backbone harness and the other is located in the VGT actuator.

On the public network, there are two 120-ohm terminating resistors, both of which are located at each end of the backbone harness.

134.

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

At what percentage does the DEF low lamp illuminate?

  • 10%

  • 5%

  • 0%

  • 20%

Correct answer: 10%

The DEF low lamp illuminates once the tank reaches 10%. At 5%, the DEF low lamp flashes, a warning buzzer alerts, and the engine derates at 80%.

Once the tank reaches 0%, vehicle speed becomes limited to 5 MPH to protect the engine.

135.

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

Regeneration is based on all of the following factors, except:

  • Ambient temperatures

  • Engine's operating conditions

  • DPF restriction level

  • Response from the driver

Correct answer: Ambient temperatures

Ambient temperatures do not play a role in regeneration. Instead, regeneration is based on the engine's operating conditions.

It also depends on the DPF restriction level and the response from the driver.

136.

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

Technician A states that fuel is injected into the exhaust system to heat the DOC. Technician B states that the DOC needs to be a minimum of 850 °F to react with the fuel.

Who is correct?

  • Technician A

  • Both A and B

  • Technician B

  • Neither A nor B

Correct answer: Technician A

The ECM commands fuel to be injected into the exhaust via the AFT injector, which heats the DOC, so technician A is correct. If the DOC does not reach 550 °F, it will not react with the fuel and heat the DPF, making technician B incorrect.

Activating the regeneration inhibit switch temporarily halts any attempts of the ECM to perform active regeneration.

137.

Technician A states that some fuel injectors are flow tested at the factory and assigned calibration codes. Technician B states that when replacing injectors, the ECM will need to be replaced and programmed with current injector calibrations.

Who is correct?

  • Technician A 

  • Technician B

  • Both A and B

  • Neither A nor B

Correct answer: Technician A

Many injectors are flow tested and given a calibration code, making technician A correct. The calibration code needs to be programmed into the ECM.

The ECM needs to be programmed but not replaced, making technican B incorrect.

138.

Technician A states that a DPF is used to trap and lower NOx. Technician B states that a DPF is used to lower hydrocarbons.

Who is correct?

  • Neither A nor B

  • Technician A

  •  Technician B

  • Both A and B

Correct answer: Neither A nor B

DPFs are used to trap soot, preventing it from flowing out of the exhaust and into the atmosphere. The diesel oxidation catalyst (DOC) chemically reacts with the exhaust gas to convert nitrogen oxide into nitrogen dioxide and to oxidize absorbed hydrocarbons.

The DOC starts the regeneration event by converting exhaust gases into heat.

139.

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

What is the normal fuel pressure at port B with the engine running at 1800 RPM?

  • 125-160 PSI

  • 40-100 PSI

  • 100-120 PSI

  • 165-185 PSI

Correct answer: 125-160 PSI

Fuel supply pressure at port B should be between 125 and 160 PSI when the engine is running at 1800 RPM. With the key on and the engine cranking, test port B should measure 40 PSI.

140.

Turbocharger shafts should be checked for axial and radial movement using which tool?

  • Dial indicator

  • Feeler gauge

  • Tape measure

  • Torque wrench

Correct answer:  Dial indicator

The turbocharger shaft should be checked for excessive movement using a dial indicator. By performing a spin test by hand, while pulling and pushing on the shaft, the technician determines if there's enough play for the turbine wheel or compressor to contact the housing, thereby requiring a replacement.

A feeler gauge is used to measure small distances, but not movement. A tape measure is used to measure distance, not movement. A torque wrench is used to measure rotational torque, not movement.