ASVAB Automotive Information — Questions and Answers

Question 1: What is the purpose of a vehicle's PCV (Positive Crankcase Ventilation) valve?

To control fuel pressure
To vent blow-by gases from the crankcase back into the intake (Correct answer)
To regulate engine coolant flow
To adjust ignition timing

Correct answer: To vent blow-by gases from the crankcase back into the intake

The PCV valve routes harmful blow-by gases from the crankcase back into the intake manifold to be burned rather than released into the atmosphere.

Question 2: Which type of brake uses hydraulic pressure to squeeze brake pads against a rotor?

Drum brake
Disc brake (Correct answer)
Band brake
Shoe brake

Correct answer: Disc brake

Disc brakes use a hydraulic caliper to squeeze brake pads against a spinning rotor, creating friction to slow the vehicle.

Question 3: What does a vehicle's alternator do while the engine is running?

Converts AC current to DC to start the engine
Generates AC current converted to DC to charge the battery and power electronics (Correct answer)
Regulates fuel injection timing
Controls transmission shifting

Correct answer: Generates AC current converted to DC to charge the battery and power electronics

The alternator generates alternating current (AC) which is converted to direct current (DC) to recharge the battery and supply power to the vehicle's electrical systems.

Question 4: What is 'engine displacement'?

The weight of the engine block
The total volume swept by all pistons in one complete revolution (Correct answer)
The distance the crankshaft travels
The fuel capacity of the engine

Correct answer: The total volume swept by all pistons in one complete revolution

Engine displacement is the total volume swept by all pistons during one complete cycle, typically measured in liters or cubic inches.

Question 5: Which component in an automatic transmission uses fluid coupling to transmit power from the engine?

Clutch pack
Torque converter (Correct answer)
Planetary gearset
Valve body

Correct answer: Torque converter

The torque converter uses fluid coupling to transmit engine power to the transmission, allowing the vehicle to stop without stalling the engine.

Question 6: What is the function of the vehicle's EGR (Exhaust Gas Recirculation) system?

To improve exhaust sound
To recirculate a portion of exhaust gases back into the intake to reduce NOx emissions (Correct answer)
To increase exhaust flow for better performance
To filter particulates from exhaust

Correct answer: To recirculate a portion of exhaust gases back into the intake to reduce NOx emissions

The EGR system recirculates a portion of exhaust gases back into the combustion chamber to lower peak combustion temperatures and reduce nitrogen oxide (NOx) emissions.

Question 7: When a car's wheel is out of balance, what is the most common symptom?

Engine misfire at idle
Vibration felt in the steering wheel or seat at highway speeds (Correct answer)
Difficulty shifting gears
Poor fuel economy at low speeds

Correct answer: Vibration felt in the steering wheel or seat at highway speeds

An unbalanced wheel creates vibration that is typically felt through the steering wheel or floorboard, especially at highway speeds.

Question 8: What does 'overhead cam' (OHC) mean in engine design?

The camshaft is located in the engine block below the cylinders
The camshaft is located in the cylinder head above the valves (Correct answer)
The camshaft is driven by a hydraulic pump
The camshaft controls fuel injection only

Correct answer: The camshaft is located in the cylinder head above the valves

In an overhead cam engine, the camshaft is mounted in the cylinder head directly above the valves, eliminating pushrods and allowing for higher RPM operation.

Question 9: What is the purpose of a vehicle's sway bar (stabilizer bar)?

To increase ground clearance
To reduce body roll during cornering by linking opposite wheels (Correct answer)
To adjust ride height automatically
To dampen engine vibration

Correct answer: To reduce body roll during cornering by linking opposite wheels

The sway bar connects opposite wheels through short links and reduces body roll during cornering by transferring force from the compressed side to the extended side.

Question 10: What type of oil rating system is used in the US to classify motor oil by viscosity?

ISO ratings
SAE ratings (Correct answer)
API ratings
ASTM ratings

Correct answer: SAE ratings

The Society of Automotive Engineers (SAE) viscosity rating system (e.g., 5W-30) classifies motor oil by its flow characteristics at cold and operating temperatures.

Question 11: A vehicle is pulling to one side when braking. What is the most likely cause?

Low engine oil
A stuck or seized brake caliper on one side (Correct answer)
A worn timing belt
A faulty alternator

Correct answer: A stuck or seized brake caliper on one side

A seized caliper on one side applies more braking force to that wheel than the other, causing the vehicle to pull toward the side with the stuck caliper.

Question 12: In a four-stroke engine, what occurs during the 'compression' stroke?

Both valves open to allow exhaust to escape
Both valves are closed while the piston moves up, compressing the air-fuel mixture (Correct answer)
The spark plug fires and ignites the mixture
The piston moves down while the intake valve opens

Correct answer: Both valves are closed while the piston moves up, compressing the air-fuel mixture

During the compression stroke, both intake and exhaust valves are closed and the piston moves upward, compressing the air-fuel mixture before ignition.

Question 13: What does the 'W' in a motor oil designation like 5W-30 stand for?

Weight
Winter (Correct answer)
Wear
Wet

Correct answer: Winter

The 'W' stands for Winter, indicating the oil's viscosity rating at low temperatures to ensure proper cold-weather starting and initial lubrication.

Question 14: Which sensor measures the amount of oxygen in the exhaust to help regulate the air-fuel mixture?

MAP sensor
O2 (oxygen) sensor (Correct answer)
MAF sensor
Throttle position sensor

Correct answer: O2 (oxygen) sensor

The oxygen sensor (O2 sensor) monitors oxygen content in exhaust gases and sends signals to the ECU to adjust the air-fuel ratio for optimal combustion and emissions.

Question 15: What is the purpose of a differential in a vehicle's drivetrain?

To increase engine torque output
To allow drive wheels to rotate at different speeds when turning (Correct answer)
To engage and disengage the drivetrain from the engine
To convert engine torque to electrical power

Correct answer: To allow drive wheels to rotate at different speeds when turning

The differential allows the outer wheel to rotate faster than the inner wheel during a turn, preventing tire scrub and allowing smooth cornering.

Question 16: What is 'detonation' (engine knock) in a gasoline engine?

Normal combustion where the spark plug ignites the mixture
Uncontrolled premature ignition of the air-fuel mixture before the spark plug fires (Correct answer)
The sound of a worn timing chain
Exhaust backfiring through the intake

Correct answer: Uncontrolled premature ignition of the air-fuel mixture before the spark plug fires

Detonation (knock) occurs when the compressed air-fuel mixture ignites spontaneously before the spark plug fires, creating a characteristic knocking sound and potentially damaging the engine.

Question 17: What is the primary function of anti-lock brakes (ABS)?

To shorten stopping distance on all surfaces
To prevent wheel lockup during hard braking, maintaining steering control (Correct answer)
To automatically apply brakes on steep hills
To reduce brake pad wear during normal driving

Correct answer: To prevent wheel lockup during hard braking, maintaining steering control

ABS prevents wheels from locking up during emergency braking by rapidly modulating brake pressure, allowing the driver to maintain steering control.

Question 18: Which component seals the combustion chamber between the cylinder block and cylinder head?

Valve stem seal
Head gasket (Correct answer)
Piston ring
Crankshaft seal

Correct answer: Head gasket

The head gasket seals the joint between the engine block and cylinder head, preventing combustion gases, coolant, and oil from mixing or leaking externally.

Question 19: What does a vehicle's mass airflow (MAF) sensor measure?

Exhaust gas temperature
The amount of air entering the engine to help calculate fuel delivery (Correct answer)
Intake manifold vacuum pressure
Engine oil temperature

Correct answer: The amount of air entering the engine to help calculate fuel delivery

The MAF sensor measures the mass of air entering the engine, and the ECU uses this data to calculate the correct fuel injection quantity for the proper air-fuel ratio.

Question 20: If a car's temperature gauge rises to the red zone while driving, what should the driver do first?

Turn on the air conditioning to cool the engine
Safely pull over and shut off the engine to prevent damage (Correct answer)
Continue driving slowly to a service station
Add cold water directly to the hot radiator

Correct answer: Safely pull over and shut off the engine to prevent damage

An overheating engine can suffer severe damage quickly; the correct response is to safely stop and shut off the engine to allow it to cool before investigating the cause.

Question 21: What type of suspension system uses a single large pivot point per wheel, with no upper control arm?

Double wishbone suspension
MacPherson strut suspension (Correct answer)
Multi-link suspension
Solid axle suspension

Correct answer: MacPherson strut suspension

MacPherson strut suspension combines the shock absorber and strut into a single unit attached to the steering knuckle, requiring only a lower control arm and no upper control arm.

ASVAB Automotive Information

What is the purpose of a vehicle's PCV (Positive Crankcase Ventilation) valve?

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