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ASE B5 Mechanical & Electrical Components study materials
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ASE B5 Mechanical & Electrical Components practice questions

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Question 1Cooling Systems

A 50/50 mixture of ethylene glycol antifreeze and water is used in a cooling system primarily because it:

  1. lowers the freeze point and raises the boiling point Correct answer.
  2. prevents the coolant from freezing at any temperature
  3. raises the freeze point without changing the boiling point
  4. raises the freeze point and lowers the boiling point

Explanation

Ethylene glycol is blended with water to depress the freeze point and elevate the boiling point, while the inhibitor package protects metals and lubricates the pump. A 50/50 blend delivers that protection while keeping heat transfer close to that of plain water.

Question 2Cooling Systems

The primary function of the radiator pressure cap is to:

  1. circulate coolant through the radiator when the engine is off
  2. raise the boiling point of the coolant by pressurizing the system Correct answer.
  3. filter debris from the coolant as it passes through the radiator
  4. vent coolant to the atmosphere whenever the engine warms up

Explanation

The cap seals the system and holds pressure, which raises the boiling point of the coolant above its atmospheric value and helps prevent boil-over. It also opens momentarily to let expanding coolant out and lets coolant be drawn back in as the system cools.

Question 3Cooling Systems

The thermostat in an engine cooling system controls:

  1. the pressure inside the radiator
  2. the amount of coolant stored in the recovery bottle
  3. the flow of coolant between the engine and the radiator Correct answer.
  4. the speed of the radiator cooling fan

Explanation

The thermostat opens and closes a valve at the coolant outlet, metering how much coolant reaches the radiator so the engine reaches and holds its designed operating temperature. Restricting flow when the engine is cold speeds warm-up and improves heater output.

Question 4Cooling Systems

On most late-model light vehicles, the coolant pump is driven by:

  1. the starter motor during cranking
  2. the camshaft through a set of timing gears
  3. the engine accessory drive belt Correct answer.
  4. a dedicated electric motor mounted on the pump shaft

Explanation

On the great majority of modern engines the coolant pump is turned by the serpentine accessory belt that also drives the alternator and A/C compressor. Electric pumps do exist on some hybrids and late-model engines, but the belt-driven pump remains standard for most vehicles.

Question 5Cooling Systems

The electric cooling fan on a front-wheel-drive car is normally commanded on when:

  1. the engine is first started from cold
  2. vehicle speed exceeds highway speed
  3. the ignition key is turned to the off position
  4. coolant temperature rises above a set threshold or the A/C is turned on Correct answer.

Explanation

The PCM turns the fan on when coolant temperature exceeds a calibrated threshold, when A/C refrigerant pressure rises, or when A/C is requested. This provides airflow through the condenser and radiator when vehicle speed alone cannot supply it.

Question 6Cooling Systems

The coolant recovery bottle allows coolant to:

  1. pressurize the system above the cap rating
  2. expand out of the radiator when hot and return when it cools Correct answer.
  3. be added to the engine oil for extra cooling
  4. be drained out and discarded when the system overheats

Explanation

As the system heats up, expanding coolant is pushed past the cap into the bottle, and as it cools the coolant is drawn back into the radiator. This keeps the radiator full and prevents air from being pulled into the system.

Question 7Cooling Systems

A customer complains that the engine never reaches normal operating temperature and the heater blows only lukewarm air. The most likely cause is:

  1. a thermostat that is stuck open Correct answer.
  2. a water pump with a leaking seal
  3. a cooling fan that runs continuously
  4. a radiator cap that releases pressure too early

Explanation

If the thermostat never closes, coolant circulates through the radiator continuously, so the engine runs below its designed temperature and the heater receives only warm coolant. Both complaints together point to a thermostat that stays open.

Question 8Cooling Systems

An engine overheats within a few minutes of a cold start, the upper radiator hose stays cool, and the heater blows cold. Which is the most likely cause?

  1. a leaking heater core
  2. a thermostat stuck closed Correct answer.
  3. an inoperative cooling fan
  4. a radiator cap with a low pressure rating

Explanation

A closed thermostat blocks coolant flow to the radiator, so the engine overheats quickly while the upper hose stays cool and the heater never gets hot coolant. Neither the radiator nor the fan can help because coolant never reaches them.

Question 9Cooling Systems

A cooling system pressure tester is installed and the gauge drops slowly with no external leak visible. A likely explanation is:

  1. a tester hose that was not bled of trapped air before the test began
  2. an internal leak past the head or intake gasket Correct answer.
  3. a coolant mixture that was richer in antifreeze than 50/50
  4. a thermostat that stayed closed throughout the whole test

Explanation

A slow, steady pressure drop with no external leak points to coolant escaping into the engine, such as through a head gasket, intake gasket, or timing cover. Such internal leaks are often confirmed by checking for coolant in the oil or by a combustion-gas test.

Question 10Cooling Systems

Both heater hoses are hot, the engine reaches normal operating temperature, but the heater blows cold air. The most likely cause is:

  1. a blend door or heater control valve fault Correct answer.
  2. a radiator that is clogged internally
  3. a worn water pump impeller
  4. a thermostat stuck open

Explanation

Hot inlet and outlet hoses show that coolant is flowing through the heater core, so the fault must be on the air side, such as a mispositioned blend door, a failed actuator, or a shut control valve. A coolant-side restriction would normally leave one hose noticeably cooler than the other.

Question 11Cooling Systems

A thermostatic fan clutch on a rear-wheel-drive vehicle should:

  1. freewheel at all times to save fuel
  2. lock solid as soon as the engine starts
  3. be replaced whenever the drive belt is replaced
  4. engage more as the air temperature through the radiator rises Correct answer.

Explanation

A thermostatic fan clutch engages progressively as the air coming through the radiator gets hotter, which is why the fan roar is heard after the engine warms. It also slips at cold temperatures and at high road speed to reduce noise and save fuel.

Question 12Cooling Systems

A voltmeter connected between the coolant and the battery negative terminal reads 0.5 V. This reading indicates:

  1. stray current that can corrode cooling system metals Correct answer.
  2. normal operation, with no action needed
  3. the charging system is overcharging
  4. the thermostat is opening too late

Explanation

A voltage reading above roughly 0.3 V between coolant and ground means stray current is flowing through the coolant, which promotes electrolysis and attacks radiators, heater cores, and gaskets. The cause is usually a poor ground or a faulty electrical component in contact with the cooling system.

Question 13Cooling Systems

Mixing an orange OAT coolant with a green conventional coolant in the same system can:

  1. improve corrosion protection by combining the additives
  2. raise the freeze point to minus 60 degrees F
  3. form a gel or sludge that can plug the heater core Correct answer.
  4. have no effect, because all coolants are chemically the same

Explanation

OAT and conventional coolants use different inhibitor chemistries, and combining them can drop the additives out of solution as a gel or sludge. That debris can plug the radiator, heater core, and small coolant passages, so coolants of different types should not be mixed.

Question 14Cooling Systems

A squealing noise comes from the front of the engine and worsens when the throttle is snapped. A stethoscope locates the noise at the water pump. The most likely cause is:

  1. a clogged heater core
  2. a low coolant level in the recovery bottle
  3. a worn pump shaft bearing Correct answer.
  4. a thermostat that opens late

Explanation

A bearing noise at the water pump changes with engine speed and is usually heard as a squeal or growl at the pump location. A rough shaft bearing can also let the pulley or fan wobble, and the pump should be replaced before the shaft fails completely.

Question 15Cooling Systems

After a coolant drain and refill, an engine overheats and the heater blows cold, even though the coolant level is correct. The next step should be to:

  1. bleed trapped air from the cooling system Correct answer.
  2. replace the radiator cap
  3. install a lower-temperature thermostat
  4. add a can of stop-leak to the radiator

Explanation

Air trapped during a refill can block flow through the heater core and form a steam pocket at the thermostat, producing exactly these symptoms. Bleeding at the highest point or using a vacuum fill tool is the standard correction, followed by rechecking the level after the engine cools.

Question 16Cooling Systems

A coolant refractometer shows the mixture is 70 percent antifreeze and 30 percent water. The result of this mixture is:

  1. no change in boiling point compared with water
  2. guaranteed freeze protection in any climate
  3. better heat transfer than a 50/50 mix
  4. reduced heat transfer and possible overheating Correct answer.

Explanation

Antifreeze carries heat less effectively than water, so a 70 percent concentration reduces heat transfer and can contribute to overheating in hot weather. The extra antifreeze buys little additional freeze protection compared with a 50/50 blend.

Question 17Cooling Systems

A 15 psi cap is used on a system where the unpressurized boiling point of the coolant is 223 degrees F. Approximately what boiling point does the cap provide? (Each 1 psi raises the boiling point about 3 degrees F.)

  1. about 283 degrees F
  2. about 268 degrees F Correct answer.
  3. about 253 degrees F
  4. about 238 degrees F

Explanation

The cap adds roughly 3 degrees F of boiling point for each pound of pressure, so 15 psi times 3 equals about 45 degrees F. Adding that to 223 degrees F gives about 268 degrees F, which is why a weak cap can allow boil-over on an otherwise healthy system.

Question 18Cooling Systems

A block tester (combustion leak detector) fluid turns from blue to yellow while the engine runs. This result indicates:

  1. the coolant is too old and should be replaced
  2. the system is overpressurized by a faulty cap
  3. combustion gases are entering the cooling system Correct answer.
  4. the thermostat is stuck open

Explanation

The test dye changes color in the presence of carbon dioxide, which is present in combustion gases but not normally in coolant. A positive result points to a head gasket, cracked head, or cracked block allowing combustion gases into the cooling system.

Question 19Cooling Systems

On a conventional V8 with a belt-driven water pump, coolant flows from the pump into the:

  1. the thermostat housing, then into the water pump inlet
  2. the block and heads, then through the thermostat to the radiator Correct answer.
  3. the radiator lower tank, then upward through the engine block
  4. the heater core, then straight back to the radiator

Explanation

The pump pushes coolant into the block and heads first, where it picks up heat, and the coolant then passes through the thermostat to the radiator to be cooled before returning to the pump inlet. This path explains why the upper hose is hot once the thermostat opens.

Question 20Cooling Systems

A vehicle loses coolant with no visible external leak, the exhaust smells sweet, and the spark plugs show a clean, steam-washed appearance. The most likely cause is:

  1. a water pump seal leaking at the weep hole
  2. a radiator cap that vents below its rated pressure
  3. trapped air in the heater core
  4. a head gasket leaking coolant into a cylinder Correct answer.

Explanation

Sweet-smelling exhaust and steam-cleaned spark plugs are classic signs of coolant being burned in a cylinder, usually from a failed head gasket or a cracked casting. A cooling system pressure test and a combustion gas test would confirm the diagnosis.

Question 21Electrical Systems

A fully charged 12-volt lead-acid battery that has rested and had its surface charge removed should show approximately what open-circuit voltage at 77°F (25°C)?

  1. 13.8 volts
  2. 12.6 volts Correct answer.
  3. 14.4 volts
  4. 11.8 volts

Explanation

Each fully charged lead-acid cell produces about 2.1 volts, and six cells in series give roughly 12.6 volts. Open-circuit voltage is meaningful only after surface charge is removed and the battery has rested.

Question 22Electrical Systems

Which statement best describes the overall purpose of the alternator in a vehicle's electrical system?

  1. It converts alternating current to direct current for the battery only
  2. It holds system voltage at exactly 12.0 volts at all times
  3. It stores energy for the next engine start
  4. It supplies current to run electrical loads and to recharge the battery Correct answer.

Explanation

While the engine runs, the alternator is the primary source of electrical power; it feeds the loads and restores the battery's charge. Internal rectification from AC to DC is one of the means it uses, not its overall purpose.

Question 23Electrical Systems

In a conventional starting system, what is the main job of the starter solenoid?

  1. It converts electrical energy into mechanical torque
  2. It reduces cranking rpm to protect the flywheel
  3. It closes the high-current circuit between the battery and the starter motor Correct answer.
  4. It limits charging current to the battery

Explanation

The solenoid is a heavy-duty relay whose contacts carry the hundreds of amps the starter draws. On many starters it also mechanically engages the drive gear, but its electrical role is switching the high-current feed.

Question 24Electrical Systems

What is the primary job of a fuse in a 12-volt automotive circuit?

  1. To add a known resistance in series with the load
  2. To protect the wiring from overheating if current becomes excessive Correct answer.
  3. To reduce the current drawn by the load
  4. To hold circuit voltage steady for sensitive loads

Explanation

A fuse is a calibrated weak link in series with the circuit; it opens when current exceeds its rating, before the wire can overheat. Its element is matched to the wire gauge and expected load, not used to regulate voltage or current.

Question 25Electrical Systems

A 12-volt circuit is connected to a resistive load of 3 ohms. How much current flows?

  1. 36 amps
  2. 4 amps Correct answer.
  3. 9 amps
  4. 0.25 amp

Explanation

Ohm's law gives current as voltage divided by resistance, so 12 divided by 3 equals 4 amps.

Question 26Electrical Systems

Two identical 6-ohm resistors are connected in series across a 12-volt source. What is the current through each resistor?

  1. 0.5 amp
  2. 4 amps
  3. 2 amps
  4. 1 amp Correct answer.

Explanation

In a series circuit the resistances add, giving 12 ohms total, so 12 volts divided by 12 ohms equals 1 amp. The same current flows through every element of a series circuit.

Question 27Electrical Systems

Which headlamp type creates light with an electric arc across electrodes in a gas-filled capsule and needs a high-voltage ballast to operate?

  1. Light-emitting diode (LED)
  2. Incandescent
  3. High-intensity discharge (HID) Correct answer.
  4. Halogen

Explanation

HID lamps strike an arc in a gas fill; the ballast supplies the high starting voltage and then limits running current. Halogen and standard incandescent bulbs use a heated filament, and LEDs emit light from a semiconductor junction.

Question 28Electrical Systems

What is the most common effect of a poor ground connection in a lighting circuit?

  1. The lamps are dim or flicker, especially when other loads are on Correct answer.
  2. System voltage rises above 15 volts
  3. The circuit fuse blows immediately
  4. The battery becomes overcharged

Explanation

A high-resistance ground creates a voltage drop in the return path, so less voltage reaches the lamp and brightness falls. Cycling loads change the current through that resistance, which makes the symptom fluctuate.

Question 29Electrical Systems

During cranking, a technician measures 0.90 volt from the battery positive post to the starter positive stud. The manufacturer's maximum is 0.20 volt. What does this indicate?

  1. A failed alternator rectifier
  2. Excessive resistance in the positive battery cable or its connections Correct answer.
  3. Normal operation, because the specification applies only to the ground side
  4. A battery that is overcharged

Explanation

Voltage-drop testing compares voltage at both ends of a conductor while current flows; more than the specified drop means resistance is too high in the cable, terminals, or connections. The ground side also has its own separate specification, so this reading is not excused by it.

Question 30Electrical Systems

A battery goes flat overnight. With all modules commanded to sleep, current at the negative battery cable measures 850 milliamps; the manufacturer's limit is 50 milliamps. What is the most likely explanation?

  1. The reading is normal for a vehicle with keyless entry
  2. The alternator is overcharging the battery
  3. The battery has too low a cold-cranking rating
  4. One or more circuits or modules stay energized after sleep Correct answer.

Explanation

Sleep current should fall to a few tens of milliamps once modules time out; 850 milliamps is many times the limit and will drain a battery overnight. The next step is to isolate the responsible circuit by fuse or module while monitoring the draw.

Question 31Electrical Systems

With the engine at 2000 rpm and electrical loads on, charging voltage measured at the battery is 12.2 volts. Specification is 13.5 to 14.8 volts. What is the most likely cause?

  1. A battery with high internal resistance only
  2. A loose starter mounting bolt
  3. A fault in the alternator or its voltage regulation Correct answer.
  4. An excessive parasitic draw

Explanation

12.2 volts is essentially battery open-circuit voltage, meaning the alternator is not delivering meaningful charge at speed with loads applied. The fault lies in the alternator, its field or control circuit, or the regulator.

Question 32Electrical Systems

On a standard ISO-style automotive relay, terminals 85 and 86 are connected to which part of the relay?

  1. Battery positive and the load
  2. The normally closed contact pair
  3. The electromagnetic coil Correct answer.
  4. The load circuit and ground

Explanation

Terminals 85 and 86 are the ends of the coil winding; energizing them pulls the armature and closes the relay. Terminals 30, 87, and 87a make up the contact side that switches load current.

Question 33Electrical Systems

Why is a diode often connected across the coil of a relay in an ECU-controlled circuit?

  1. To prevent the relay contacts from arcing as they close
  2. To suppress the voltage spike produced when coil current is switched off Correct answer.
  3. To stop the battery from discharging through the coil
  4. To reduce the coil's steady holding current

Explanation

A coil resists changes in current, so when the driver opens the circuit the collapsing magnetic field generates a high reverse voltage. The diode gives that energy a safe path and protects the switching transistor.

Question 34Electrical Systems

Why are the two conductors of a CAN bus twisted together in a pair?

  1. To increase the current-carrying capacity of each wire
  2. To allow the bus to operate at a higher voltage
  3. To reduce electromagnetic interference and radiated emissions Correct answer.
  4. To provide a redundant power feed to the modules

Explanation

Twisting the pair makes both wires see nearly the same interfering fields, so noise appears as common-mode voltage that the differential receiver rejects. Twisting also limits loop area, which reduces radiated emissions.

Question 35Electrical Systems

A Hall-effect crankshaft position sensor produces which type of output?

  1. A variable resistance that rises with engine speed
  2. A steady analog voltage that changes only with temperature
  3. A digital square-wave signal as the target wheel's teeth pass the sensor Correct answer.
  4. A fixed 5-volt reference that never changes

Explanation

The sensor's internal circuitry switches its output as the magnetic field is interrupted by the reluctor teeth, producing a square wave. The PCM uses the frequency of that signal to calculate speed and position.

Question 36Electrical Systems

A windshield wiper motor operates at both low and high speed but stops wherever it is when the switch is turned off instead of returning to park. What is the most likely cause?

  1. A faulty park switch or its circuit in the motor assembly Correct answer.
  2. A failed wiper switch high-speed contact
  3. An open high-speed brush in the motor
  4. A blown fuse for the wiper circuit

Explanation

Parking is controlled by a separate switch inside the motor gearbox that keeps the motor powered until it reaches the park position. If both speeds work, the motor and main feeds are good, leaving the park circuit as the fault.

Question 37Electrical Systems

A power window on one door does not move when either the master switch or the door switch is operated, but the motor runs when it is powered directly from a battery. What is the most likely cause?

  1. A faulty window regulator
  2. An open circuit in the wiring or ground between the switches and the motor Correct answer.
  3. A blown fuse that feeds the entire window system
  4. A failed master switch only

Explanation

Because the motor runs when jumped, the motor and regulator are functional; the fault lies in the control path shared by both switches, such as the motor feed or its ground. A single failed switch would not disable both controls.

Question 38Electrical Systems

A battery reads 12.6 volts open-circuit. Under a load of half its cold-cranking rating for 15 seconds at 70°F, voltage falls to 9.2 volts. How should this result be interpreted?

  1. The result is normal for a fully charged battery
  2. The battery is good but needs recharging
  3. The test is invalid because the surface charge was not removed
  4. The battery fails the load test and should be replaced Correct answer.

Explanation

A good battery at 70°F should hold at least about 9.6 volts during this test; 9.2 volts indicates it cannot deliver its rated current. The open-circuit reading of 12.6 volts shows it was charged, so the failure is capacity rather than state of charge.

Question 39Electrical Systems

How does a fusible link differ from a standard blade fuse in a main power feed?

  1. It resets itself after a fault is corrected
  2. It is a slow-blow high-current wire section that protects main feeds and is replaced after melting Correct answer.
  3. It protects only the starter motor circuit
  4. It has a lower current rating than any blade fuse

Explanation

A fusible link is a short length of special wire, typically four gauge sizes smaller than the circuit it protects, that melts under sustained overload. Its thermal inertia lets it ride through brief high-current surges that would open a fast fuse.

Question 40Electrical Systems

What is the purpose of the neutral safety switch in the starting circuit?

  1. To allow cranking only when the transmission is in Park or Neutral Correct answer.
  2. To prevent the transmission from being shifted with the key off
  3. To keep the starter engaged until the engine fires
  4. To limit engine rpm in neutral

Explanation

The switch is in series with the starter control circuit and opens unless the selector is in Park or Neutral, preventing the vehicle from cranking in gear. On modern vehicles this function is often handled by the transmission range sensor.

Question 41Electrical Systems

A charging system produces normal DC output voltage, but AC ripple measured at the battery is 0.6 volt AC with loads on. What is the most likely cause?

  1. A loose battery hold-down clamp
  2. Worn alternator slip-ring brushes
  3. One or more failed rectifier diodes in the alternator Correct answer.
  4. An open field circuit in the alternator

Explanation

The rectifier converts stator AC into DC; a failed diode leaves part of the AC waveform unfiltered, so ripple rises while average voltage may still look acceptable. Excessive ripple under load points to diode or stator faults.

Question 42Electrical Systems

A 12-volt source has 0.4 ohm of total resistance in its cables and connections and feeds a 2.0-ohm load. What voltage appears across the load?

  1. 9.6 volts
  2. 10.0 volts Correct answer.
  3. 11.0 volts
  4. 12.0 volts

Explanation

Total circuit resistance is 2.4 ohms, so current is 12 divided by 2.4, or 5 amps. The drop across the load is 5 times 2.0, or 10 volts, with the remaining 2 volts lost in the cables.

Question 43Electrical Systems

During cranking, battery post voltage is 11.9 volts and the voltage at the starter positive stud is 9.5 volts. The battery passed a load test. What is the best conclusion?

  1. The readings are normal for a cold engine
  2. The starter motor has excessive internal resistance
  3. There is excessive resistance in the starter feed or ground circuit Correct answer.
  4. The battery is failing under load

Explanation

A 2.4-volt difference between battery and starter indicates a large voltage drop in the cables, terminals, or ground path, well beyond the usual 0.2 to 0.5 volt limits. A healthy battery holding 11.9 volts during cranking supports this conclusion.

Question 44Electrical Systems

With the sensor disconnected, a 5-volt reference circuit measures 5.00 volts. With the sensor connected, the same point measures 0.20 volt. What is the most likely cause?

  1. An open in the reference wire between the PCM and the sensor
  2. A short to ground in the sensor or its wiring Correct answer.
  3. Normal operation of a ratiometric sensor
  4. High resistance in the sensor ground return wire only

Explanation

The reference is intact because it reads 5.00 volts unloaded; connecting the sensor pulls it down to 0.20 volt, meaning current is flowing to ground through a low resistance. That points to a shorted sensor or a chafed reference wire, not an open.

Question 45Electrical Systems

After a battery replacement, charging voltage at the battery is 15.6 volts and the battery becomes warm and gasses. Which is the most likely cause?

  1. A failed alternator rectifier diode
  2. A sulfated battery with high internal resistance
  3. Excessive parasitic draw on the battery
  4. A faulty voltage regulator or an open voltage-sense circuit Correct answer.

Explanation

Normal charging voltage is about 13.5 to 14.8 volts; 15.6 volts overcharges the battery and causes gassing and heat. The regulator, or the sense line it uses to judge battery voltage, is the control element that should prevent this.

Question 46Electrical Systems

An electrical load connected to a 12-volt battery draws 5 amperes. How much power does the load consume?

  1. 17 watts
  2. 0.42 watt
  3. 60 watts Correct answer.
  4. 2.4 watts

Explanation

Power in a DC circuit equals voltage multiplied by current. Multiplying 12 volts by 5 amperes gives 60 watts.

Question 47Electrical Systems

Two 12-ohm resistors are connected in parallel across a 12-volt source. What is the total current supplied by the source?

  1. 2 A Correct answer.
  2. 24 A
  3. 1 A
  4. 0.5 A

Explanation

Each 12-ohm branch sees the full 12 volts, so each branch draws 1 ampere. In a parallel circuit, branch currents add, giving 2 amperes total.

Question 48Electrical Systems

To measure current through a circuit branch, how should an ammeter be connected?

  1. Across the power source
  2. Between the branch and ground only
  3. In series with the branch Correct answer.
  4. In parallel with the load

Explanation

An ammeter has very low resistance and must carry the current being measured, so it is connected in series with the branch. Connecting it in parallel can create a high-current path and damage the meter or circuit.

Question 49Electrical Systems

What is the primary purpose of a fuse in an automotive circuit?

  1. To regulate voltage to sensitive modules
  2. To store energy for intermittent loads
  3. To limit current by adding resistance during normal operation
  4. To open the circuit on excess current Correct answer.

Explanation

A fuse is a sacrificial current-limiting device. Its element melts when current exceeds its rating, opening the circuit before wiring or components are damaged.

Question 50Electrical Systems

Which function does the rectifier bridge perform in an alternator charging system?

  1. It regulates rotor field current to control output voltage.
  2. It steps battery voltage up to a higher charging voltage.
  3. It converts battery direct current into alternating current for the stator.
  4. It rectifies stator alternating current into direct current. Correct answer.

Explanation

The alternator stator produces alternating current as the rotor field sweeps past its windings. The rectifier bridge uses diodes to convert that AC into DC for the battery and electrical loads.