ASVAB Auto and Shop: Engine Systems and Repair — Questions and Answers

Question 1: What is the purpose of the engine's cooling system?

To lubricate engine parts
To prevent the engine from overheating (Correct answer)
To filter fuel
To regulate air intake

Correct answer: To prevent the engine from overheating

The cooling system maintains proper engine temperature to prevent overheating.

The cooling system uses a coolant (antifreeze/water mixture) circulated by a water pump through passages in the engine block and head. Heat absorbed from combustion is transferred to the radiator, which dissipates it into the air.

Question 2: What is the role of the alternator in a vehicle?

Start the engine
Recharge the battery and power electrical systems while running (Correct answer)
Control fuel injection
Cool the engine

Correct answer: Recharge the battery and power electrical systems while running

The alternator generates electricity to recharge the battery and power accessories while the engine runs.

The alternator is a generator driven by a belt connected to the engine's crankshaft. It produces AC electricity that is converted to DC to charge the battery and power lights, ignition, and other electrical components while the engine is running.

Question 3: What do spark plugs do in a gasoline engine?

Filter the air-fuel mixture
Ignite the compressed air-fuel mixture in each cylinder (Correct answer)
Measure fuel pressure
Seal the combustion chamber

Correct answer: Ignite the compressed air-fuel mixture in each cylinder

Spark plugs produce an electrical spark that ignites the air-fuel mixture at the right moment.

Spark plugs receive high-voltage current from the ignition coil and produce a spark across a small gap inside each cylinder. This spark ignites the compressed air-fuel mixture at the precise moment needed in the combustion cycle.

Question 4: What is the function of the oil pump?

Inject oil into the fuel
Circulate oil throughout the engine to reduce friction (Correct answer)
Filter dirty oil
Measure oil pressure

Correct answer: Circulate oil throughout the engine to reduce friction

The oil pump circulates engine oil to lubricate moving parts and reduce friction and heat.

The oil pump draws oil from the oil pan and forces it through passages to critical engine components such as bearings, the camshaft, and valve train. This lubrication reduces friction and wear, and helps cool parts not reached by the coolant.

Question 5: What is a four-stroke engine cycle?

Intake, Compression, Exhaust, Power
Intake, Combustion, Compression, Exhaust
Intake, Compression, Power, Exhaust (Correct answer)
Fuel, Air, Fire, Exhaust

Correct answer: Intake, Compression, Power, Exhaust

The four strokes are Intake, Compression, Power (combustion), and Exhaust.

The four-stroke cycle: 1) Intake — piston moves down, drawing in air-fuel mixture; 2) Compression — piston moves up, compressing the mixture; 3) Power — spark ignites the mixture, pushing piston down; 4) Exhaust — piston moves up again, expelling burned gases.

Question 6: What does the radiator do?

Stores fuel
Cools engine coolant by dissipating heat into the air (Correct answer)
Filters exhaust gases
Pressurizes the fuel system

Correct answer: Cools engine coolant by dissipating heat into the air

The radiator transfers heat from hot coolant to the surrounding air.

The radiator is a heat exchanger that cools the engine coolant. Hot coolant from the engine passes through thin metal tubes with fins. Airflow (from driving or the cooling fan) passes over the fins, removing heat and cooling the coolant before it recirculates.

Question 7: What is the purpose of the timing belt or chain?

Connects the battery to the starter
Synchronizes the crankshaft and camshaft rotation (Correct answer)
Controls gear shifts
Drives the water pump only

Correct answer: Synchronizes the crankshaft and camshaft rotation

The timing belt/chain ensures the crankshaft and camshaft rotate in precise synchrony.

The timing belt or chain connects the crankshaft to the camshaft(s), ensuring that intake and exhaust valves open and close at the correct moments relative to piston position. A broken timing belt can cause catastrophic engine damage.

Question 8: What is the function of the catalytic converter?

Increase fuel efficiency
Reduce harmful emissions from exhaust gases (Correct answer)
Cool exhaust gases
Muffle engine noise

Correct answer: Reduce harmful emissions from exhaust gases

The catalytic converter uses chemical reactions to convert harmful exhaust gases into less harmful ones.

The catalytic converter contains precious metal catalysts (platinum, palladium, rhodium) that convert harmful exhaust pollutants: carbon monoxide (CO) → CO₂; hydrocarbons → CO₂ and H₂O; nitrogen oxides (NOx) → N₂.

Question 9: What does a torque wrench measure?

The speed of tightening
The rotational force applied to a fastener (Correct answer)
The thread pitch of a bolt
The tensile strength of a bolt

Correct answer: The rotational force applied to a fastener

A torque wrench measures and controls the rotational force applied when tightening bolts.

A torque wrench allows the user to apply a specific amount of rotational force (torque) to a fastener. In engine work, proper torque specifications ensure critical components like cylinder head bolts are tightened correctly for sealing and safety.

Question 10: What is the function of the fuel injector?

Filter fuel before it enters the engine
Spray atomized fuel into the intake manifold or cylinder (Correct answer)
Store fuel under pressure
Mix fuel with exhaust gases

Correct answer: Spray atomized fuel into the intake manifold or cylinder

Fuel injectors spray a precise, atomized mist of fuel into the combustion chamber.

Fuel injectors are electronically controlled valves that spray atomized fuel into the intake manifold or directly into the cylinder. This precise metering improves fuel efficiency and reduces emissions compared to older carburetor systems.

Question 11: What causes engine 'knocking' or 'pinging'?

Loose spark plugs
Premature ignition of the air-fuel mixture (Correct answer)
Low oil pressure
Broken timing chain

Correct answer: Premature ignition of the air-fuel mixture

Knocking occurs when the air-fuel mixture ignites before the spark plug fires, causing double combustion events.

Engine knock (detonation) occurs when the compressed air-fuel mixture ignites spontaneously before the spark plug fires, creating pressure waves that collide. This can damage pistons and bearings. Higher-octane fuel resists premature ignition.

Question 12: What is the purpose of motor oil viscosity ratings (e.g., 10W-30)?

Indicate oil color
Describe oil's resistance to flow at different temperatures (Correct answer)
Specify the amount of oil needed
Measure oil purity

Correct answer: Describe oil's resistance to flow at different temperatures

Viscosity ratings describe how oil flows at cold (W = winter) and operating temperatures.

Viscosity ratings like 10W-30 indicate oil thickness. The '10W' describes viscosity at cold start (lower number = flows more easily in cold), and '30' describes viscosity at operating temperature. Multi-grade oils maintain consistent lubrication across temperature ranges.

Question 13: What does a vehicle's differential do?

Regulates fuel delivery
Allows drive wheels to rotate at different speeds during turns (Correct answer)
Controls brake pressure
Adjusts suspension height

Correct answer: Allows drive wheels to rotate at different speeds during turns

The differential allows the outer wheel to rotate faster than the inner wheel in a turn.

When a vehicle turns, the outer wheels travel a larger arc than the inner wheels and must rotate faster. The differential is a gear assembly between the drive wheels that distributes torque while allowing each wheel to turn at a different speed.

Question 14: What is the purpose of the vehicle's air filter?

Remove water from fuel
Filter dust and debris from air entering the engine (Correct answer)
Cool incoming air
Regulate airflow speed

Correct answer: Filter dust and debris from air entering the engine

The air filter prevents dirt and debris from entering the engine's intake and causing wear.

The air filter removes particulates from the air before it enters the engine's combustion chambers. A clean air filter is essential for engine efficiency; a clogged filter restricts airflow, reducing power and fuel economy.

Question 15: What is the function of the crankshaft?

Open and close valves
Convert the pistons' up-and-down motion into rotational motion (Correct answer)
Store fuel for combustion
Control ignition timing

Correct answer: Convert the pistons' up-and-down motion into rotational motion

The crankshaft converts the linear motion of pistons into rotational energy to drive the drivetrain.

The crankshaft is connected to each piston via connecting rods. As pistons move up and down during combustion, the crankshaft converts this linear reciprocating motion into rotational motion, which is then transmitted through the transmission to the wheels.

Question 16: What does bleeding the brakes accomplish?

Adds fresh brake fluid
Removes air bubbles from the brake lines (Correct answer)
Adjusts brake pressure
Cleans brake rotors

Correct answer: Removes air bubbles from the brake lines

Bleeding brakes removes air that can cause a spongy, ineffective brake pedal.

Brake systems rely on incompressible hydraulic fluid. Air in the lines is compressible, which reduces braking effectiveness (spongy pedal). Bleeding forces fresh fluid through the system to expel trapped air bubbles.

Question 17: What is a caliper in a disc brake system?

The rotating disc attached to the wheel
The component that holds and applies the brake pads to the rotor (Correct answer)
The brake fluid reservoir
The ABS control unit

Correct answer: The component that holds and applies the brake pads to the rotor

The brake caliper houses the brake pads and hydraulically squeezes them against the rotor to slow the wheel.

The disc brake caliper is a hydraulic clamp that straddles the rotor. When the brake pedal is pressed, hydraulic pressure forces pistons in the caliper outward, pressing the brake pads against both sides of the spinning rotor to create friction and slow the vehicle.

Question 18: What is the purpose of the PCV (Positive Crankcase Ventilation) valve?

Pressurize the fuel system
Recirculate blow-by gases from the crankcase back into the intake (Correct answer)
Release pressure from the cooling system
Control valve timing

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

The PCV valve routes crankcase gases back into the intake to be burned, reducing emissions.

Combustion gases that slip past piston rings ('blow-by') accumulate in the crankcase. The PCV valve routes these gases back through the intake manifold to be re-burned, preventing oil contamination, crankcase pressure buildup, and hydrocarbon emissions.

Question 19: What does an engine compression test measure?

Fuel pressure in the injectors
The pressure built up in each cylinder during the compression stroke (Correct answer)
Oil viscosity under pressure
Exhaust back pressure

Correct answer: The pressure built up in each cylinder during the compression stroke

A compression test checks the sealing ability of the piston rings, valves, and head gasket in each cylinder.

A compression test uses a pressure gauge threaded into each spark plug hole. With the engine cranked, it measures the maximum pressure developed in each cylinder. Low readings may indicate worn piston rings, burned valves, or a blown head gasket.

Question 20: What is the function of the master cylinder in a brake system?

Generate brake force at the wheel
Convert pedal force into hydraulic pressure (Correct answer)
Store brake pads
Control ABS activation

Correct answer: Convert pedal force into hydraulic pressure

The master cylinder converts the mechanical force from pressing the brake pedal into hydraulic pressure.

When the brake pedal is pressed, it pushes a piston inside the master cylinder, pressurizing the brake fluid. This hydraulic pressure is transmitted through the brake lines to the calipers or wheel cylinders at each wheel to apply the brakes.

Question 21: What does the acronym OBD-II stand for?

Onboard Battery Diagnostic II
Onboard Diagnostics II (Correct answer)
Overhead Brake Detection II
Output Boost Detector II

Correct answer: Onboard Diagnostics II

OBD-II (Onboard Diagnostics II) is the standard vehicle diagnostic system that monitors emissions and engine performance.

OBD-II (Onboard Diagnostics, second generation) is a standardized system in vehicles since 1996 that continuously monitors engine, transmission, and emission-related components. When a fault is detected, it stores a diagnostic trouble code (DTC) and illuminates the check engine light.

Question 22: What is the function of a flywheel?

Filter engine oil
Store rotational energy to smooth engine output and assist starting (Correct answer)
Control air intake
Drive the cooling fan

Correct answer: Store rotational energy to smooth engine output and assist starting

The flywheel stores rotational energy to smooth power delivery and provides mass for the starter motor to engage.

The flywheel is a heavy rotating disc attached to the crankshaft. Its inertia smooths out the intermittent pulses of combustion, providing steadier rotational output. It also has a ring gear around its outer edge that the starter motor engages to crank the engine.

Question 23: What tool would you use to measure the inner diameter of a cylinder bore?

Micrometer
Dial bore gauge (Correct answer)
Vernier caliper
Feeler gauge

Correct answer: Dial bore gauge

A dial bore gauge measures the internal diameter of a cylinder to check for wear or out-of-round conditions.

A dial bore gauge (or cylinder bore gauge) has spring-loaded contact probes that expand inside a cylinder bore. It measures the exact inner diameter, allowing a technician to check for wear, taper, or oval distortion requiring reboring.

Question 24: What is the purpose of a serpentine belt?

Connect the crankshaft to the camshaft
Drive multiple engine accessories with a single belt (Correct answer)
Seal the timing cover
Regulate coolant flow

Correct answer: Drive multiple engine accessories with a single belt

A serpentine belt drives accessories like the alternator, power steering pump, and AC compressor from a single belt.

The serpentine belt is a single, long ribbed belt that winds around multiple pulleys to drive engine accessories such as the alternator, water pump, power steering pump, and air conditioning compressor. It replaced multiple individual V-belts in modern engines.

Question 25: What does it mean when a vehicle 'hydroplanes'?

The engine overheats from water cooling failure
The tires lose contact with the road surface due to water buildup (Correct answer)
Coolant enters the combustion chamber
The brakes fail due to wet rotors

Correct answer: The tires lose contact with the road surface due to water buildup

Hydroplaning occurs when water builds up under tires faster than they can displace it, lifting them off the road.

Hydroplaning occurs when a wedge of water builds up in front of a tire faster than it can be displaced, causing the tire to ride on a layer of water and lose traction. It typically occurs at speeds above 35 mph on wet roads, especially with worn tires.

Question 26: What is the function of a vehicle's camshaft?

Drive the fuel pump directly
Open and close the intake and exhaust valves in time with the pistons (Correct answer)
Generate electrical current
Control the throttle body

Correct answer: Open and close the intake and exhaust valves in time with the pistons

The camshaft controls the precise timing and duration of valve opening and closing.

The camshaft is a shaft with oval-shaped lobes (cams) that push open the intake and exhaust valves at precise moments during the engine cycle. It is driven by the timing belt or chain from the crankshaft and rotates at half the crankshaft speed in a 4-stroke engine.

Question 27: What is the purpose of antifreeze (coolant) in the engine?

Only to lower the freezing point of water
To prevent freezing in winter, prevent boiling in summer, and inhibit corrosion (Correct answer)
To lubricate the water pump
To increase fuel octane

Correct answer: To prevent freezing in winter, prevent boiling in summer, and inhibit corrosion

Antifreeze lowers the freezing point and raises the boiling point of coolant, and contains corrosion inhibitors.

Antifreeze (ethylene glycol) mixed with water lowers the freezing point to around -34°F and raises the boiling point above 250°F. It also contains corrosion inhibitors that protect the metal components of the cooling system from rust and scale.

Question 28: What is the purpose of the EGR (Exhaust Gas Recirculation) valve?

Increase exhaust flow
Recirculate exhaust gases into the intake to reduce NOx emissions (Correct answer)
Filter exhaust particulates
Increase engine temperature

Correct answer: Recirculate exhaust gases into the intake to reduce NOx emissions

The EGR valve reduces combustion temperatures, which lowers the formation of nitrogen oxides (NOx).

The EGR valve routes a portion of exhaust gas back into the intake manifold. This dilutes the air-fuel mixture and reduces peak combustion temperatures, which inhibits the formation of nitrogen oxides (NOx) — a major air pollutant.

Question 29: What type of wrench is best suited for preventing rounded bolt heads?

Open-end wrench
Box-end (closed) wrench (Correct answer)
Adjustable wrench
Pipe wrench

Correct answer: Box-end (closed) wrench

A box-end wrench surrounds all sides of the bolt head, distributing force evenly and reducing rounding risk.

A box-end wrench has a closed loop that encircles the nut or bolt head, gripping all sides simultaneously. This distributes torque evenly, unlike an open-end wrench which contacts only two sides and is more likely to slip and round off corners.

Question 30: What is a head gasket and what happens when it fails?

A rubber seal for the oil cap; causes oil leaks
A seal between the engine block and cylinder head; failure allows coolant and oil to mix or combustion gases to escape (Correct answer)
A gasket for the exhaust manifold; causes exhaust leaks
A filter gasket; reduces fuel flow

Correct answer: A seal between the engine block and cylinder head; failure allows coolant and oil to mix or combustion gases to escape

The head gasket seals the engine block and head; failure can mix coolant with oil or allow compression loss.

The head gasket seals the mating surfaces between the cylinder head and engine block, containing combustion pressure and keeping coolant and oil passages separate. When it fails, coolant may enter cylinders (white exhaust smoke), oil and coolant may mix, or compression may drop.

Question 31: What does 'dead reckoning' mean in navigation context for vehicle operators?

Stopping the vehicle for a position check
Estimating current position based on known starting point, speed, and direction (Correct answer)
Using GPS exclusively
Reading road signs to determine route

Correct answer: Estimating current position based on known starting point, speed, and direction

Dead reckoning estimates position using a known start point, speed, heading, and elapsed time.

Dead reckoning is a navigation method where current position is estimated from a known previous position by accounting for speed, heading, and time elapsed. Military vehicle operators use it when electronic navigation is unavailable or unreliable.

Question 32: What is the function of the throttle body in a fuel-injected engine?

Store fuel under pressure
Control the amount of air entering the engine based on accelerator position (Correct answer)
Inject fuel into cylinders
Regulate exhaust flow

Correct answer: Control the amount of air entering the engine based on accelerator position

The throttle body contains a valve that opens and closes to control airflow into the intake manifold.

The throttle body is located between the air filter and intake manifold. It contains a butterfly valve controlled by the accelerator pedal (or electronically in drive-by-wire systems) that regulates the volume of air entering the engine, thereby controlling engine power and speed.

Question 33: What would cause white smoke to come from a vehicle's exhaust pipe?

Rich fuel mixture
Burning oil
Coolant entering the combustion chamber (Correct answer)
Clogged air filter

Correct answer: Coolant entering the combustion chamber

White smoke from exhaust typically indicates coolant (water) is being burned in the cylinders.

White or sweet-smelling smoke from the exhaust indicates coolant is entering the combustion chamber and being burned. This is commonly caused by a blown head gasket, cracked cylinder head, or cracked engine block. Blue smoke indicates burning oil; black smoke indicates a rich fuel mixture.

Question 34: What is the role of brake fluid?

Lubricate the brake pads
Transmit hydraulic pressure from the master cylinder to the brake calipers (Correct answer)
Cool the rotors
Prevent rotor rust

Correct answer: Transmit hydraulic pressure from the master cylinder to the brake calipers

Brake fluid is the hydraulic medium that transfers force from the pedal to the brakes at each wheel.

Brake fluid is a hydraulic fluid that transmits the force from the master cylinder to wheel cylinders or calipers. Because liquids are nearly incompressible, pressure applied at the pedal is efficiently transmitted to the brakes. Brake fluid also has a high boiling point to resist vaporizing under heat.

ASVAB Auto and Shop: Engine Systems and Repair

What is the purpose of the engine's cooling system?

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