DFFT Electrical Systems 2

Question 1

A vehicle's horn does not work. The fuse is intact. What should be tested next?

Accepted Answer

The horn relay and the horn switch continuity

Answer

The battery state of charge

Answer

The alternator output voltage

Answer

The main body control module

Question 2

A vehicle's headlights flicker at idle but are steady at higher RPM. What is the most likely cause?

Accepted Answer

Low alternator output at idle not meeting electrical demand

Answer

A loose headlight bulb socket

Answer

A failing headlight switch

Answer

A discharged battery with a dead cell

Question 3

During a DFFT electrical test, you find 0.8V voltage drop across a battery-to-starter cable under cranking load. Is this acceptable?

Accepted Answer

No, maximum allowable voltage drop is typically 0.5V for high-current cables

Answer

Yes, 0.8V is within the standard acceptable range

Answer

It depends on the battery's cold cranking amp rating

Answer

Yes, as long as the engine cranks normally

Question 4

A vehicle's battery goes flat overnight despite no obvious loads left on. What is this fault called?

Accepted Answer

Parasitic drain or key-off current draw

Answer

A faulty battery with reduced capacity

Answer

An alternator that overcharges the battery

Answer

A short circuit in the ignition circuit

Question 5

What is the correct method to test for a parasitic drain on a vehicle?

Accepted Answer

Connect an ammeter in series between the battery negative terminal and the cable

Answer

Connect a voltmeter across the battery terminals with the ignition off

Answer

Use an ohmmeter to measure resistance across all fuses

Answer

Start the engine and measure alternator output current

Question 6

A vehicle's check engine light is on and a scan tool shows a P0300 random misfire code. What sensor data should be examined first?

Accepted Answer

Live misfire counter data per cylinder and ignition system output

Answer

Fuel trim short-term and long-term values only

Answer

Engine coolant temperature sensor voltage

Answer

Throttle position sensor sweep data