ASE L2 Exam Questions

Page 10 of 15

181.

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

How many pins does the J1939 data link connector for the private network have?

  • Three pins

  • Five pins

  • Seven pins

  • Nine pins

Correct answer: Three pins

The J1939 data link connector (engine compartment) for the private network contains three pins. It allows the engine ECM to talk with other vehicle control systems, such as the VGT, EGR, and exhaust aftertreatment.

It's not to be confused with the J1939 data link connector (in-cab), which is part of the public network. The in-cab data link connector contains nine pins.

182.

Technician A states that switches are open by default. Technician B states that switches are used to open or close a circuit.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician B

Switches either open or close a circuit, making technician B correct. Schematics help to determine whether a switch is designed to be open or closed by default.

When reading the voltage, it should show high or low voltage depending on whether the switch is opened or closed.

183.

Technician A states that when an engine has low fuel volume, the pump should be replaced and rechecked. Technician B states that when an engine has low fuel volume, the filter should be replaced and rechecked.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician B

If fuel volume is low on a diesel engine, the fuel filter should be replaced and the volume rechecked rather than replacing a good fuel pump. Fuel filters are a maintenance item and should be replaced at the manufacturer service interval.

Aeration of the fuel system should also be checked.

184.

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

The engine cranks but will not start. Scan tool data displays 4500 PSI at the fuel rail when cranking. Technician A states that diagnostics should start with the fuel system. Technician B states that diagnostics should start with engine compression.

Who is correct?

  • Technician A 

  • Technician B

  • Both A and B

  • Neither A nor B

Correct answer: Technician A

The minimum start-up pressure at the fuel rail is 5000 PSI. Using the scan tool data, the logical starting point of diagnostics would be the fuel system.

Based on this information, there's no evidence to suggest a problem with engine compression.

185.

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

What is the maximum voltage measurement of the TCM when viewed with a scan tool?

  • 16 volts

  • 14 volts

  • 12 volts

  • 5 volts

Correct answer: 16 volts

The TCM supply voltage measurement range displayed on diagnostic equipment is between 0 and 16 volts . The TCM is mounted to the transmission, and delivers a regulated 5-volt supply.

It receives information from several modules, actuators, sensors, and switches to provide transmission output that's varied for desired fuel economy, emissions control, and driveability.

186.

Technician A states that vehicle information includes information on the software used by the ECM. Technician B states that the software information can be obtained using a diagnostic data reader.

Who is correct?

  • Both A and B 

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Software information can be found in two ways: reading the vehicle information or using the diagnostic data reader. If a fleet includes two vehicles of the same model year, one may have a later software version because of the production date.

Based on the information provided, the vehicles may also require different diagnostic procedures.

187.

Technician A states that the wastegate on a variable turbocharger is used to control boost. Technician B states that boost pressure on a variable turbocharger is controlled by the turbo charger vanes.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician B

On a variable turbocharger, the vanes mounted to the unison ring control the boost, making technician B correct. As the unison ring turns, the vanes change the angle.

Due to the adjustable vanes, a wastegate is not used or needed, so technician A is incorrect.

188.

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

What happens to the sensor voltage as the temperature rises in the intake manifold pressure sensor?

  • It drops

  • It rises

  • It remains the same

  • There's no voltage reading

Correct answer: It drops

The intake manifold pressure sensor contains four wires. Its primary purpose is to monitor the pressure within the intake manifold.

As the temperature rises, the sensor voltage drops. Sensor voltage measures between 0.50 and 4.50 volts, depending on the temperature.

189.

Technician A states that when experiencing multiple failures, look for something that all the components have in common. Technician B states that if multiple failures occur and there is a module in common, that module should be replaced first.

Who is correct?

  • Technician A

  • Technician B

  • Both A and B

  • Neither A nor B

Correct answer: Technician A

When diagnosing a vehicle with multiple failures, the technician should start by examining the schematic for something in common. Locating the related connectors, splices, fuses, and modules can save the technician money and time. 

All components in common should be tested before replacing them. Only after the related components are checked, should a module replacement be considered.

190.

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

If a multimeter set on the voltage setting was connected between terminal 2 and 3 at the DEF pressure sensor with the key on and engine off, what should the reading be?

  • 5 volts

  • 12 volts 

  • 16 volts

  • 0 volts

Correct answer: 5 volts 

Terminal 3 is a 5-volt reference and terminal 2 is ground — a meter hooked between should read 5 volts. The DEF pressure sensor is located in the DEF pressure line.

The ECM takes this signal to monitor pressures going to the DEF doser valve.

191.

When scanning the engine KOEO (key on engine off), what temperature should the sensors on a cold engine read?

  • Ambient temperature

  • 195 to 220 °F

  • 40 to 75 °F

  • 140 to 240 °F

Correct answer: Ambient temperature

Troubleshooting should always begin with a cold engine. Scanning the engine should occur KOEO (key on engine off).

At this stage, all of the sensors of the cold engine should have ambient temperature readings. If there's a sensor with a significantly different temperature reading than the others, it needs more attention.

192.

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

Technician A states that the DEF supply pump contains an inlet screen. Technician B states that the DEF supply pump contains an outlet filter.

Who is correct? 

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

The DEF supply pump contains both an inlet screen and an outlet filter, making both technicians correct. The pump supplies DEF to the doser valve at a pressure of 130 PSI.

At key OFF, the ECM tells the DEF supply pump to reverse rotation and clear the lines by grounding its directional control circuit.

193.

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

What is barometric pressure at sea level?

  • 29.9 inHg

  • 26 inHg

  • 24 inHg

  • 19.1 inHg

Correct answer: 29.9 inHg

The barometric pressure sensor reads from sea level to 12,000 feet. Pressure varies between 29.9 and 19.1 inHg.

At sea level, the barometric pressure reading is 29.9 Hg. This reading creates a corresponding voltage of 4.25.

194.

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

How long after the key is shut off will the fuel pressure control solenoid hold 5,000 PSI?

  • 30 seconds

  • 15 seconds

  • 45 seconds

  • 1 minute

Correct answer: 30 seconds

The solenoid defaults to the closed position when the key is turned off and will hold 5,000 PSI for 30 seconds. It regulates fuel pressure in combination with the fuel volume control solenoid.

There's also a spring-loaded relief fail-safe set at 35,000 PSI (241,317 kPa).

195.

The fuel system can be checked for air in all of the following ways, except:

  • Use gauge to check fuel pressure

  • With a liquid eye

  • With a clear tubing piece on the suction side of the fuel system

  • Submerge the return fuel line in a container of fuel

Correct answer: Use gauge to check fuel pressure

A fuel gauge isn't going to help the technician find air in the fuel system.

A liquid eye is a valuable tool when looking for air. The technician can also use a clear tubing piece on the suction side of the fuel system before the transfer pump and operate the engine to see if air is traveling with the fuel. Additionally, submerging the return fuel line in a container with fuel is helpful when starting the engine because bubbles could end up in the return fuel stream if air is in the system.

196.

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

What commands the variable geometry turbocharger actuator?

  • ECM

  • BCM

  • TCM

  • ICM

Correct answer: ECM

The variable geometry turbocharger (VGT) actuator is commanded by the ECM. It's mounted on the turbocharger.

The VGT actuator directs an internal sliding nozzle to ensure control of the turbine shaft speed. When communication fails, the VGT defaults to the fully open position.

197.

Diesel fuel injectors typically fall into how many different types?

  • Two

  • Three

  • Four

  • Five

Correct answer: Two

There are two basic types of injectors: nozzle injectors and unit injectors. Nozzle fuel injectors use a distributor or injection pump for distribution. With the unit injectors, the pump or distributor isn't needed. These injectors produce enough pressure to run on their own.

198.

Technician A states that the ohmmeter function can be used to check the continuity of a circuit. Technician B states that the ohmmeter function is used to check the continuity of a live circuit.

Who is correct?

  • Technician A

  • Technician B

  • Both A and B

  • Neither A nor B

Correct answer: Technician A

The ohmmeter function of a digital multimeter (DMM) verifies the continuity of circuits. It also measures the resistance of components.

An ohmmeter is self-powered, so it should never be used on a live component or circuit.

199.

Technician A states that when performing a boost pressure check, the engine should be at idle. Technician B states that when performing a boost pressure check, the engine should be operated at full engine load.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician B

When performing a boost pressure check, the engine must be operated under full load. Boost pressure should be checked before and after the charge air cooler.

Readings vary between engines, so the manufacturer's specifications should always be consulted.

200.

Technician A states that a diesel engine that has an exhaust stream with white smoke indicates a blown head gasket. Technician B states that a diesel engine with a white exhaust stream indicates unburned fuel.

Who is correct?

  • Technician B

  • Technician A

  • Neither A nor B

  • Both A and B

Correct answer: Technician B

White smoke from the diesel exhaust indicates unburned fuel. It can be caused by damaged or malfunctioning injectors, low compression, or engine temperature that's not hot enough. It may show up more often during a cold start.

A blown head gasket is often combined with steam coming from the exhaust. Steam indicates that coolant has entered the combustion chamber.