Electrical and Electronic Systems Flashcards

A technician notices the battery warning light flickers at idle but goes off at higher RPM. What should be checked first?

Answer: The drive belt tension and alternator output at idle

Flickering at idle suggests the alternator is not producing sufficient output at low RPM, which could be caused by a slipping or worn drive belt, or an alternator with a failing stator winding or diode.

What is the purpose of the diode trio in an alternator?

Answer: To supply DC current to the rotor field coil from the stator output

The diode trio taps a small portion of AC output from the stator, rectifies it to DC, and feeds it to the rotor field coil. This makes the alternator self-exciting after initial field current from the battery.

What is the correct procedure for testing a fuse without removing it from the fuse box?

Answer: Use a test light or voltmeter to check for power on both sides of the fuse with the circuit energized

Testing both exposed test points on top of a blade fuse with a test light or voltmeter while the circuit is on confirms power is passing through. If only one side has power, the fuse is blown.

What causes alternator whine in the audio system?

Answer: AC ripple from a failing rectifier diode coupling into the audio signal wiring

A failing diode in the rectifier bridge allows AC ripple to pass into the DC electrical system. This AC noise couples into audio signal wiring, producing a whine that increases in pitch with engine RPM.

A vehicle equipped with daytime running lights (DRLs) has one DRL that does not illuminate. The headlights work normally. What is the most likely cause?

Answer: A burned-out DRL bulb or LED unit

Since the headlights work normally, the bulb wiring and ground are functional. The most likely cause is a burned-out DRL-specific bulb or LED unit, as many vehicles use separate elements for DRL and headlight functions.

What does a waveform with missing humps on an alternator AC ripple test indicate?

Answer: One or more failed rectifier diodes

A normal three-phase alternator produces a smooth ripple pattern. Missing humps indicate that one or more rectifier diodes have failed, preventing that phase's output from contributing to the DC supply.