FREE 310T Electrical and Electronic Systems Questions and Answers

Question 1

A technician is diagnosing a truck with a 'cranks but does not start' condition.
The starter motor turns the engine over at a normal speed, but the engine fails to fire.
The batteries, starter, and fuel delivery to the injection pump have been verified as good.
Which of the following electrical system faults is the MOST likely cause?

Accepted Answer

A faulty engine crankshaft position sensor.

Answer

A failed alternator diode.

Answer

An open circuit in the glow plug relay.

Answer

High resistance in the battery ground cable.

Question 2

While performing a parasitic draw test on a heavy-duty truck, a technician measures a steady current of 450 milliamps (0.45A) after all modules have entered sleep mode. What is the next logical step in this diagnostic procedure?

Accepted Answer

Begin removing fuses one by one while monitoring the ammeter.

Answer

Replace the batteries as they are likely failing.

Answer

Perform a voltage drop test on the starter circuit.

Answer

Load test the alternator.

Question 3

A technician is troubleshooting a communication failure on a J1939 CAN bus network. Using a multimeter, they measure the resistance between the CAN High (Pin C) and CAN Low (Pin D) terminals at the diagnostic connector and get a reading of 120 ohms. What does this reading indicate?

Accepted Answer

One of the two terminating resistors is missing or has failed.

Answer

The CAN bus wiring is shorted to power.

Answer

The CAN bus wiring is shorted to ground.

Answer

The CAN bus network is operating correctly.

Question 4

Which of the following BEST describes the primary advantage of a multiplexed electrical system in a modern truck?

Accepted Answer

It reduces the amount and complexity of wiring by allowing multiple electronic control modules to communicate over a shared data bus.

Answer

It increases the amperage capacity of individual circuits, allowing for more powerful accessories.

Answer

It provides a dedicated, hard-wired circuit for every switch and component, improving reliability.

Answer

It eliminates the need for fuses and circuit breakers by using self-resetting electronic components.

Question 5

A truck's headlights are dim, and the battery voltage with the engine running at high idle is only 12.5 volts. The battery itself has been load-tested and is in good condition. Which of the following is the MOST likely cause of these symptoms?

Accepted Answer

A faulty alternator or voltage regulator.

Answer

A parasitic draw draining the battery.

Answer

High resistance in the headlight ground circuit.

Answer

A failed starter solenoid.

Question 6

A technician observes that the exterior lights on a trailer are not working correctly when connected to a specific tractor. The lights on the tractor itself function properly. Before checking the trailer wiring, what is the MOST appropriate first step to diagnose the issue at the tractor-trailer connection?

Accepted Answer

Use a commercial trailer light tester to check the output signals at the tractor's 7-way connector.

Answer

Measure the resistance of each circuit in the trailer's pigtail cord.

Answer

Bypass the 7-way connector by using jumper wires between the tractor and trailer.

Answer

Replace all the bulbs on the trailer as a precaution.