Question 1

The current flow through an inductor cannot instantly change from one level to another. However, the voltage measured across an inductor can instantly change from one level to another.

Accepted Answer

The current through an inductor cannot change instantaneously due to the inductor's property of opposing changes in current, but the voltage across it can change instantly as it is proportional to the rate of change of current.

Question 2

An in-range failure always results in a DTC being set.

Accepted Answer

An in-range failure may not always set a Diagnostic Trouble Code (DTC) because it might not exceed the predefined thresholds that trigger a code.

Question 3

In a closed-loop control system, error = desired output - measured output.

Accepted Answer

In a closed-loop control system, the error is calculated as the difference between the desired output (setpoint) and the measured output (feedback) to adjust the system's input and achieve the desired performance.

Question 4

Exhaust gas recirculation (EGR) is used to reduce particulate matter (PM) exhaust emissions.

Accepted Answer

Exhaust gas recirculation (EGR) is primarily used to reduce nitrogen oxides (NOx) emissions, not particulate matter (PM).

Question 5

A spark plug and ignition coil is typically used in an SCR system to cause the DEF to ignite.

Accepted Answer

SCR (Selective Catalytic Reduction) systems use DEF (Diesel Exhaust Fluid) to reduce emissions, not to ignite fuel, so they do not require spark plugs or ignition coils.

Question 6

The injection control pressure (ICP) of a HEUI fuel system is controlled by which device?

Accepted Answer

The Injection Pressure Regulator (IPR) controls the oil pressure in the high-pressure oil system, which in turn controls the injection control pressure (ICP) in a HEUI fuel system.

Question 7

Technician A says that cam-actuated unit injectors use a common high pressure pump to develop injection pressures. Technician B says that a single-actuator EUI typically has two electrical terminals. Who is correct?

Accepted Answer

Technician B is correct. A single-actuator Electronic Unit Injector (EUI) typically has two electrical terminals. Technician A is incorrect because cam-actuated unit injectors do not use a common high-pressure pump; instead, they use the camshaft to actuate the injector directly.

Question 8

Which of the following failures would most likely illuminate the MIL lamp?

Accepted Answer

The MIL (Malfunction Indicator Lamp) is typically triggered by issues related to emissions control systems. A disconnected DEF (Diesel Exhaust Fluid) dosing injector connector would affect emissions and likely illuminate the MIL lamp.

Question 9

Technician A says that a pending DTC always results in a confirmed DTC. Technician B says that an electronic service tool can be used to clear a permanent DTC. Who is correct?

Accepted Answer

A pending DTC does not always result in a confirmed DTC as it may not meet the criteria for confirmation. A permanent DTC cannot be cleared with an electronic service tool; it clears itself once the fault is no longer detected after a certain number of drive cycles.

Question 10

Technician A says that the best way to check for a misfiring cylinder on a high-pressure common rail fuel system is to crack each injector line open one by one. Technician B says that it may be necessary to use an electronic service tool to enter new injector calibration information into the ECM memory if an injector is replaced. Who is correct?

Accepted Answer

Cracking injector lines is not recommended for high-pressure systems due to safety risks and potential damage. Using an electronic service tool to update ECM with new injector calibration is necessary when replacing injectors.

Question 11

A 2007 diesel engine with a DOC and DPF has an internal problem with cylinder 2 which causes insufficient compression for ignition. What might be a likely indication of this failure other than an engine performance complaint?

Accepted Answer

A higher DOC outlet temperature compared to the inlet when DPF regeneration is not occurring can indicate unburned fuel or incomplete combustion, often due to insufficient compression in a cylinder.

Question 12

Technician A says that a variable geometry turbocharger (VGT) may be used to regulate EGR flow. Technician B says that a smart actuator may be used to control the position of a variable geometry turbocharger. Who is correct?

Accepted Answer

Variable geometry turbochargers can indeed be used to regulate EGR flow by adjusting the exhaust pressure, and smart actuators are commonly used to control the position of VGT vanes.

Question 13

Which of the following would be considered to be a type of in-cylinder exhaust emissions reduction?

Accepted Answer

EGR reduces emissions by recirculating a portion of the exhaust gas back into the engine's cylinders. This helps to lower combustion temperatures and reduce the formation of NOx emissions.

Question 14

Technician A says that the ECM may determine the amount of soot in the DPF by measuring the differential pressure across the DPF. Technician B says that the ECM may calculate or estimate the amount of soot in the DPF based on fuel consumption and the time since the last regeneration. Who is correct?

Accepted Answer

Both technicians are correct. The ECM can use differential pressure to measure soot levels and can also estimate soot accumulation based on fuel consumption and time since the last regeneration.

Question 15

Which of the following is a true statement?

Accepted Answer

All the statements are true: A) Reaction rates generally increase with temperature due to higher kinetic energy. B) The conversion of hydrocarbons (HC) into heat in a Diesel Oxidation Catalyst (DOC) involves chemical reactions. C) The oxidation of soot in a Diesel Particulate Filter (DPF) is a chemical reaction.

Question 16

The most important inputs for an electronic unit injector diesel engine include engine speed, the operators speed or torque request (accelerator), and _____.

Accepted Answer

The engine crankshaft position is crucial for timing the fuel injection accurately in relation to the piston's position in the cylinder.

Question 17

Technician A says that a 2010 SCR system that only has one NOx sensor at the SCR catalyst outlet would likely use a virtual sensor for the SCR catalyst inlet NOx determination. Technician B says that a smart sensor and a virtual sensor are really the same thing. Who is correct?

Accepted Answer

A virtual sensor can be used to estimate the NOx levels at the SCR catalyst inlet when only one physical sensor is present at the outlet. A smart sensor and a virtual sensor are not the same; a smart sensor has built-in processing capabilities, while a virtual sensor uses software algorithms to estimate values.

Question 18

A work order indicates that a truck with a 2007 EPA diesel engine is low on power. Which of these would be the first step of the troubleshooting process?

Accepted Answer

The first step in any troubleshooting process is to verify the complaint to ensure that the issue is accurately identified before proceeding with any repairs or replacements.

Question 19

A 2010 EPA diesel engine cranks but will not start. Which of the following could be a cause?

Accepted Answer

An empty fuel tank would prevent the engine from starting as there is no fuel to combust.

Question 20

An electronic service tool indicates the following information for a diesel engine in a truck that has been parked inside the garage overnight:
- Engine Coolant Temperature: 23°C (73°F)
- Intake Manifold Air Temperature: 7°C (45°F)
- Inlet Air Temperature (air cleaner): 24°C (75°F)
- DOC Inlet Temperature: 24°C (75°F)
What do these readings indicate?

Accepted Answer

The intake manifold air temperature is significantly lower than the other temperatures, which suggests an in-range failure of the intake manifold air temperature measurement system.

Quiz 14: Diesel Engine Electronics