310T Electrical and Electronic Systems Questions and Answers

Question 1

A technician measures the resistance between the CAN High and CAN Low pins (6 and 14) on a standard J1939 diagnostic connector with the key off and batteries disconnected.
The multimeter reads 120 ohms.
What is the MOST likely cause of this reading?

Accepted Answer

One of the two terminating resistors is missing or has an open circuit.

Answer

A short circuit between the CAN High and CAN Low wires.

Answer

Both terminating resistors are functioning correctly in parallel.

Answer

An electronic control unit (ECU) on the network is internally shorted.

Question 2

A coach is brought to the shop with a complaint of the right-side marker lights flickering intermittently. The bulbs and light housings appear to be in good condition. Which of the following is the MOST likely underlying cause?

Accepted Answer

A poor ground connection for the lighting circuit.

Answer

A faulty flasher module.

Answer

An alternator that is slightly overcharging.

Answer

The body control module (BCM) needs reprogramming.

Question 3

What is the primary advantage of a multiplexing (MUX) electrical system in a modern truck compared to a conventional wiring system?

Accepted Answer

It significantly reduces the number of wires, simplifying diagnostics and reducing potential failure points.

Answer

It increases the voltage available to components for brighter lights.

Answer

It allows for the use of less expensive, lower-gauge wiring.

Answer

It eliminates the need for fuses and circuit breakers by using smart switches.

Question 4

A technician is performing a parasitic draw test on a truck that fails to hold a charge overnight. After connecting a multimeter in series with the negative battery cable, the reading stabilizes at 450 milliamps (0.45 A). What is the next logical step in the diagnostic process?

Accepted Answer

Begin pulling fuses one by one while monitoring the multimeter reading.

Answer

Replace the batteries as they are likely failing to hold a charge.

Answer

Start the engine to test the alternator's charging output.

Answer

Disconnect the starter motor power cable to check for a short.

Question 5

During a charging system analysis on a heavy-duty truck with the engine running, a technician notices the headlights are dim and the system voltage is 12.5V. Which of the following conditions is the MOST likely cause?

Accepted Answer

A faulty voltage regulator or failing alternator.

Answer

A fully charged battery with high internal resistance.

Answer

An open circuit in the starter solenoid.

Answer

Excessive resistance in the battery ground cable.

Question 6

The SAE J1939 standard is a high-level protocol used for communication and diagnostics between ECUs on a commercial vehicle. On which underlying network technology is J1939 built?

Accepted Answer

Controller Area Network (CAN)

Answer

Ethernet

Answer

LIN Bus

Answer

FlexRay

A technician measures the resistance between the CAN High and CAN Low pins (6 and 14) on a standard J1939 diagnostic connector with the key off and batteries disconnected.The multimeter reads 120 ohms.What is the MOST likely cause of this reading?

A technician measures the resistance between the CAN High and CAN Low pins (6 and 14) on a standard J1939 diagnostic connector with the key off and batteries disconnected.
The multimeter reads 120 ohms.
What is the MOST likely cause of this reading?