Electrical Systems & Emissions Control Flashcards

During a voltage drop test on the positive battery cable while cranking, what is the generally accepted maximum reading?

Answer: 0.5 volts

A cable drop above about 0.5 V under cranking load indicates excessive resistance from corrosion or a poor connection.

After all modules go to sleep, what is a typical maximum acceptable parasitic draw on most modern vehicles?

Answer: About 50 milliamps

Most manufacturers allow roughly 20-50 mA of key-off draw, and anything higher can drain the battery over days.

What open-circuit voltage indicates a fully charged 12-volt lead-acid battery at room temperature?

Answer: 12.6 volts

A fully charged battery rests at about 12.6 V, while 12.0 V is only about 25% charged.

With the engine running and loads moderate, what charging system voltage range is normal for most vehicles?

Answer: 13.5 to 14.5 volts

Regulators typically hold system voltage around 13.5-14.5 V to charge the battery without overcharging it.

A 12-volt circuit has a total resistance of 4 ohms. How much current flows?

Answer: 3 amps

By Ohm's law, I = E / R, so 12 V divided by 4 ohms equals 3 A.

A technician measures 1.2 volts AC at the alternator output with the engine running. What is the most likely cause?

Answer: A failed rectifier diode

AC ripple above about 0.5 V indicates a faulty diode letting alternating current pass into the DC system.

On a standard ISO automotive relay, which terminals are connected to the control coil?

Answer: 85 and 86

Terminals 85 and 86 energize the coil, while 30 and 87 form the switched load circuit.