Question 1

Which of the following is a major advantage of using an FET as a switch relay over a conventional relay?

Accepted Answer

FETs have very high input resistance, meaning almost no current flows into the gate, making them efficient for switching applications.

Question 2

Technician A says that ladder switches can perform as a toggle switch. Technician B says that some smart switches are multi-function. Who is correct?

Accepted Answer

Ladder switches can indeed function as toggle switches, allowing them to switch between two states. Smart switches are often designed to be multi-functional, offering more than just on/off capabilities, such as dimming, color change, or integration with home automation systems.

Question 3

Technician A says that the bus topology used in CAN 2.0/ J1939 ensures that no single module networked to the bus has more importance than any other. Technician B says that it is almost impossible to add controllers (SAs) to a J1939 data bus after it has been manufactured. Who is correct?

Accepted Answer

Technician A is correct because in a bus topology, all modules (nodes) are connected to a single communication line equally, ensuring no single module has priority over others. Technician B is incorrect because adding controllers (Source Addresses or SAs) to a J1939 data bus is feasible and common in practice, allowing for system expansion or modification.

Question 4

What is the advantage of using FETs as relays in multiplexed truck chassis?

Accepted Answer

FETs (Field-Effect Transistors) are advantageous in multiplexed truck chassis applications because they can be switched with small currents, have a fast response to control gate signals, and are generally inexpensive, making them suitable for various electronic switching applications.

Question 5

When an FET output permits excessive current flow on a multiplexed chassis, what circuit protection device opens the circuit?

Accepted Answer

A virtual fuse is a circuit protection device that opens the circuit when an FET output permits excessive current flow on a multiplexed chassis.

Question 6

What is the usual voltage differential of a J1939 message stop bit?

Accepted Answer

The answer of What is the usual voltage differential of...

Question 7

When a voltage of value of 12 volts is measured off the CAN high line of a properly functioning J1939 data backbone, what is happening?

Accepted Answer

When a voltage of 12 volts is measured off the CAN high line of a properly functioning J1939 data backbone, it typically indicates a bus wake-up. This is because the J1939 standard, used in heavy-duty vehicles, operates with a nominal voltage of 24 volts, and a 12-volt measurement on the CAN high line can signal that the bus is transitioning from a dormant state to an active state, initiating communication among connected devices.

Question 8

What is the usual low bit voltage on a J1939 data transaction?

Accepted Answer

The usual low bit voltage on a J1939 data transaction is 1 volt.

Question 9

Which of the following is known as the dominant bit in a J1939 multiplexing transaction?

Accepted Answer

The answer of Which of the following is known as...

Question 10

Technician A says that any J1939 data bus can be accessed by connecting through a green 9-pin Deutsch connector. Technician B says that a J1939 data bus backbone can be accessed through a 3-pin Deutsch connector. Who is correct?

Accepted Answer

A J1939 data bus backbone can be accessed through a 3-pin Deutsch connector, and any J1939 data bus can be accessed by connecting through a green 9-pin Deutsch connector.

Question 11

Technician A says that the contents of any data bus message packet can be interpreted using a high frequency scopemeter. Technician B says that a scopemeter can be used to identify bus node activity ... or lack of activity. Who is correct?

Accepted Answer

Both A and B are correct. A scopemeter can be used to interpret the contents of any data bus message packet, as well as identify bus node activity or lack of activity.

Question 12

When a J1939 bus experiences a dead short to the power side of the circuit, what is the likely outcome?

Accepted Answer

When a J1939 bus experiences a dead short to the power side of the circuit, it typically results in the shutdown of all bus communications. This is because the short circuit disrupts the electrical signals that are necessary for the nodes on the bus to communicate with each other.

Question 13

When a J1939 bus shorts to the ground side of the circuit, what is the likely outcome?

Accepted Answer

When a J1939 bus shorts to the ground side of the circuit, it typically results in a shutdown of all bus communications. This is because the J1939 protocol relies on a differential signal to communicate between nodes, and a short to ground disrupts this signaling, preventing any communication on the bus.

Question 14

Technician A says that J1939 node activity can be identified using a DMM set on V-DC min-max mode. Technician B says that the V-DC min-max readings taken while verifying J1939 bus activity should run between a low of 1 volt and a high of 5 volts. Who is correct?

Accepted Answer

The answer of Technician A says that J1939 node activity...

Question 15

If a voltmeter is connected between J1939 CAN-low (positive test lead) and ground (negative test lead), what is the lowest measurement you would read if the data bus is functioning properly?

Accepted Answer

The J1939 CAN (Controller Area Network) bus system operates with a voltage differential, where the CAN-low line typically varies around 2.5 volts when idle and can go as low as approximately 1.5 volts when transmitting data. Therefore, the lowest measurement one would expect to read when the data bus is functioning properly and the voltmeter is connected between CAN-low and ground would be around 1 volt, considering the potential drop from its idle state.

Question 16

Technician A says that a green 9-pin J1939 DLC must be used to connect to a post-2014 truck powertrain data bus. Technician B says that the black 9-pin J1939 DLC cannot connect to a post-2104 data bus. Who is correct?

Accepted Answer

Technician A is correct because post-2014 trucks use the green 9-pin Deutsch connector for the J1939 data bus, which is the standard for newer vehicles. The green connector signifies compliance with the newer, faster CAN standards. Technician B's statement is incorrect because it contains a typographical error with the year "2104" instead of "2014", and also, the black 9-pin connector can still connect but is associated with older protocols and might not support all functionalities of newer systems.

Question 17

What could result if an EST that is not auto-bus detect capable (ABDC) is connected to a post-2014 J1939 data bus??

Accepted Answer

Connecting an EST that is not auto-bus detect capable (ABDC) to a post-2014 J1939 data bus can result in a complete bus shutdown due to incompatibility issues, potentially disrupting communication across the entire network.

Question 18

?What prevents a black 9-pin J1939 DLC from connecting to a green 9-pin J1939 receptacle?

Accepted Answer

The answer of ?What prevents a black 9-pin J1939 DLC...

Question 19

When you have to work with multiple OEM chassis data bus systems, which type of communication adapter (CA) is recommended??

Accepted Answer

A generic RP 1210 Communication Adapter (CA) is recommended for working with multiple OEM chassis data bus systems because it is designed to be compatible with a wide range of manufacturers and protocols, providing a versatile tool for diagnostics and programming across different vehicle types.

Question 20

When troubleshooting a J1939 bus, what has occurred if a suspect parameter group (SPG) is assigned to a component??

Accepted Answer

When a suspect parameter group (SPG) is assigned to a component in a J1939 bus, it indicates that the component is reporting an abnormal condition or circuit. This does not necessarily mean the component has failed completely but is an alert to a potential issue that needs further investigation.

Quiz 36: Multiplexing