Electrical and Electronic Systems Flashcards

A fully rested battery shows an open-circuit voltage of 12.4 volts. Its approximate state of charge is:

Answer: 75%

About 12.6 V is full charge and 12.4 V corresponds to roughly 75% state of charge.

During a battery load test at 70°F (21°C) using half the CCA rating for 15 seconds, voltage should not fall below:

Answer: 9.6 volts

A good battery maintains at least 9.6 V at 70°F during a 15-second half-CCA load test.

With the battery disconnected, resistance measured between CAN High and CAN Low at DLC pins 6 and 14 on a healthy high-speed CAN bus should be about:

Answer: 60 ohms

Two 120-ohm terminating resistors in parallel produce about 60 ohms total.

A fuse blows instantly every time a circuit is switched on. The most likely cause is:

Answer: A short to ground before the load

A short to ground ahead of the load bypasses its resistance, causing excessive current that blows the fuse.

A starter cranks slowly while drawing much higher than specified current. Which is the most likely cause?

Answer: Shorted starter armature or engine mechanical binding

High current with slow cranking points to excessive load such as a shorted armature or a tight engine.

Which starter solenoid winding is effectively de-energized once the solenoid's main contacts close?

Answer: Pull-in winding

Once the contacts close, both ends of the pull-in winding see equal voltage, so only the hold-in winding keeps the plunger engaged.

An engine coolant temperature sensor is a negative temperature coefficient (NTC) thermistor. As coolant temperature rises, its resistance:

Answer: Decreases

NTC thermistors lose resistance as temperature increases.