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In a four-stroke internal combustion engine, what are the four strokes in order?
- Compression, intake, power, exhaust
- Intake, compression, power (combustion), exhaust ✓
- Power, intake, exhaust, compression
- Intake, power, compression, exhaust
The four-stroke cycle (Otto cycle, used in most gasoline car engines) operates in this sequence: (1) INTAKE — piston moves DOWN; intake valve OPEN, exhaust valve CLOSED; air-fuel mixture drawn into cylinder; (2) COMPRESSION — piston moves UP; both valves CLOSED; air-fuel mixture compressed to high p…
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What is the function of pistons in an internal combustion engine?
- To produce electrical current
- To slide up and down within cylinders, compressing the air-fuel mixture and transferring force from combustion to the connecting rod and crankshaft ✓
- To filter air
- To cool the engine
Major moving parts of a piston engine: (1) PISTONS — slide up and down in cylinders; compress mixture; receive force from combustion; equipped with PISTON RINGS that seal against the cylinder wall, control oil, and conduct heat to the cylinder; pistons made of aluminum alloy (light and conducts heat…
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What is the primary function of a spark plug?
- To inject fuel into the cylinder
- To produce a high-voltage spark across its electrodes, igniting the compressed air-fuel mixture in the cylinder at the precise moment in the engine cycle ✓
- To filter air going into the engine
- To cool the cylinder
Spark plug: produces an electric spark in the combustion chamber to ignite the air-fuel mixture. Located in each cylinder head, screwed into the engine. Structure: central electrode (high voltage), ground electrode (return path), ceramic insulator (between electrodes), metal shell (grounds to engine…
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Modern gasoline engines use what system to deliver fuel into the engine?
- Carburetor
- Electronic fuel injection (EFI), spraying precisely metered fuel through injectors into the intake manifold (port injection) or directly into the cylinder (direct injection) ✓
- Gravity feed
- Manual pump
Fuel delivery systems, evolution: (1) CARBURETOR (older, pre-1990s) — uses venturi effect (Bernoulli's principle) and mechanical metering; air drawn through narrowing passage creates low pressure, drawing up fuel from float bowl; mixed with air, drawn into intake; simple, no electronics needed, but …
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What is the main function of an automotive transmission?
- Cool the engine
- Change gear ratios between the engine and drive wheels, allowing the engine to operate efficiently across a wide range of vehicle speeds; multiplies torque at lower gears and conserves engine RPM at higher gears ✓
- Generate electricity
- Filter exhaust
Transmission: provides selectable gear ratios between the engine's crankshaft and the drive wheels. Without a transmission, engines (which need to spin in a specific RPM range — typically 600-7000 RPM) couldn't efficiently propel a car across all speeds (0-80+ mph). Lower gears multiply torque (more…
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In a manual transmission vehicle, what is the function of the clutch?
- It pumps fuel to the engine
- It engages and disengages the engine from the transmission, allowing gear changes and smooth starts from a stop without stalling the engine ✓
- It applies the brakes
- It controls the radio
Clutch: a friction-based coupling that connects/disconnects the engine to/from the transmission. When the driver presses the clutch pedal, the clutch DISENGAGES (engine spins independently of transmission), allowing: (1) Smooth start from stop without stalling (engine maintains running RPM while car…
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What is the basic operating principle of automotive brakes?
- Magnets stopping the wheels
- Friction — brake pads or shoes press against rotating disks (rotors) or drums attached to the wheels, converting the vehicle's kinetic energy into heat and slowing the vehicle ✓
- Electric current
- Air pressure only
Automotive braking: applies friction between stationary parts (pads/shoes) and rotating parts (rotors/drums attached to wheels). This converts the vehicle's KINETIC ENERGY (½mv²) into HEAT through friction — energy is conserved, just transformed. The heat is dissipated to surrounding air. Two main b…
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What is the primary purpose of automotive shock absorbers?
- Lifting the vehicle's weight
- Damping the up-and-down motion of the springs after hitting a bump, preventing continuous bouncing and keeping the tires in contact with the road ✓
- Steering the car
- Charging the battery
Suspension system: the components between the vehicle's body/frame and the wheels that allow the wheels to move up and down independently while supporting the vehicle, absorbing road shocks, and maintaining tire contact with the road. Key components: (1) SPRINGS — SUPPORT the vehicle's weight; absor…
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How does an automotive cooling system work?
- Engines don't need cooling
- Coolant (water + antifreeze) is circulated by a water pump through engine passages, absorbing heat; the hot coolant flows to the radiator where airflow (from vehicle motion and fan) removes the heat; thermostat regulates flow to maintain operating temperature ✓
- Air-only cooling for all modern engines
- The engine cools by burning less fuel
Most modern engines use LIQUID COOLING because internal combustion creates enormous heat (combustion gases reach 2000°F+ internally); without cooling, engine components would melt or seize. Liquid cooling components: (1) COOLANT — typically a 50/50 mix of WATER and ETHYLENE GLYCOL ANTIFREEZE (also p…
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What is the function of motor oil in an engine?
- It is the fuel that the engine burns
- Lubricates moving parts to reduce friction and wear, helps cool the engine, cleans by carrying contaminants to the filter, seals piston rings against cylinder walls, and prevents corrosion ✓
- It cools the radiator only
- It only adds weight
Motor oil has five primary functions: (1) LUBRICATION — reduces friction between moving parts (pistons in cylinders, crankshaft and bearings, camshaft, valves, timing components); without lubrication, metal-on-metal contact causes rapid wear, heat buildup, and seizure; (2) COOLING — circulates throu…
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What is the function of the alternator in a vehicle's electrical system?
- It starts the engine
- Generates electrical power while the engine is running, charging the battery and providing power for all vehicle electrical systems (lights, radio, computers, ignition, etc.) ✓
- Stores fuel
- Cools the engine
Automotive electrical system: BATTERY provides power to START the engine and run electronics when engine is off; ALTERNATOR generates power once engine is running, recharging the battery and supplying all electrical loads. Alternator (modern AC generator) components: (1) ROTOR — electromagnet driven…
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What is engine displacement?
- How much the engine weighs
- The total volume of all engine cylinders combined, calculated by (bore area × stroke × number of cylinders), commonly measured in liters (L) or cubic inches (CID) ✓
- How fast the engine spins
- Fuel tank size
Engine displacement: total volume swept by all cylinders during one engine cycle. Calculation: displacement = (π × bore²/4) × stroke × number of cylinders. BORE = cylinder diameter; STROKE = piston travel distance from top dead center to bottom dead center. Units: LITERS (L) (1L = 1000 cc) — modern …
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What is the function of a vehicle's exhaust system?
- Cools the engine
- Routes exhaust gases away from the engine and passengers, reduces noise, reduces emissions through catalytic conversion, and provides backpressure tuning for engine performance ✓
- Brings air into the engine
- Powers the radio
Exhaust system components: (1) EXHAUST MANIFOLD (or HEADERS) — collects exhaust gases from each cylinder and combines them; cast iron (manifold) or steel tubing (headers — performance, equal-length tubes for optimal scavenging); (2) DOWN PIPE — connects manifold to rest of system; (3) CATALYTIC CONV…
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What is the function of the differential in a vehicle's drivetrain?
- It generates power
- Allows the drive wheels to rotate at different speeds when needed (e.g., in turns), while still transferring power from the driveshaft to the wheels ✓
- Cools the engine
- Stores fuel
Differential: a gear arrangement in the drive axle that allows the two drive wheels to rotate at DIFFERENT SPEEDS while still receiving power from the driveshaft/transaxle. Why needed: when a vehicle turns, the OUTSIDE wheel must travel a longer distance than the INSIDE wheel (larger radius), so it …
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What is the purpose of a tire's tread?
- To make the tire heavier
- Provides traction by channeling water away (resisting hydroplaning), gripping irregular surfaces, and dispersing heat; tread depth is essential for wet/winter traction ✓
- Just for appearance
- To increase fuel consumption
Tire tread: the patterned rubber that contacts the road. Functions: (1) CHANNELS WATER away from the tire-road interface, preventing HYDROPLANING (tire riding on top of water film); deeper tread = more water displaced; (2) PROVIDES MECHANICAL GRIP on irregular surfaces (gravel, snow, ice, off-road);…
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What is the difference between a gasoline (Otto cycle) engine and a diesel engine?
- Gasoline engines are bigger
- Gasoline engines mix fuel with air before compression and use a spark plug to ignite; diesel engines compress air alone to very high pressure (heating it), then inject fuel which ignites from compression heat — no spark plug; diesels have higher compression ratios and more torque ✓
- Diesel engines use only kerosene
- There is no significant difference
Gasoline (Otto cycle) vs Diesel engine differences: (1) IGNITION: gasoline uses SPARK IGNITION (spark plug fires the air-fuel mixture); diesel uses COMPRESSION IGNITION (high compression heats air to 700-900°F, sufficient to ignite injected fuel — no spark plug); (2) FUEL DELIVERY: modern gasoline u…
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What is the purpose of a vehicle's catalytic converter?
- Make the exhaust louder
- Convert harmful exhaust pollutants (carbon monoxide CO, hydrocarbons HC, and nitrogen oxides NOx) into less harmful compounds (CO₂, H₂O, N₂) through catalyzed chemical reactions ✓
- Generate more power
- Cool the engine
Catalytic converter: emission control device that converts toxic combustion byproducts into less toxic substances. Located in the exhaust system after the manifold (often two — one close to engine for fast warmup, another under floor). Catalyst materials: PLATINUM, PALLADIUM, RHODIUM — precious meta…
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What is the basic principle behind how a hydraulic brake system works?
- Electricity to the wheels
- Pascal's Principle: pressure applied to a confined fluid is transmitted equally throughout; pressing brake pedal pressurizes brake fluid, which travels through lines to push pistons in calipers/wheel cylinders that force pads against rotors/drums ✓
- Gears and chains
- Magnetic attraction
Hydraulic brake systems use Pascal's Principle: pressure in a confined fluid is transmitted equally in all directions. Force amplification: small force on small-area piston creates pressure (P = F/A); same pressure on large-area piston creates large force (F = P × A). This allows reasonable pedal pr…
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What is the function of an engine's intake system?
- Stores fuel
- Filters incoming air and routes it through the throttle and intake manifold to the cylinders, where it mixes with fuel for combustion; may include sensors for the ECU ✓
- Routes exhaust gases
- Cools the cylinders
Intake system components: (1) AIR INTAKE — opening at the front of the engine bay; modern designs are 'cold air intakes' drawing from cooler areas (denser air = more power); (2) AIR FILTER — paper or oiled gauze filter; traps dirt, dust, debris; replace per maintenance schedule (typically 15,000-30,…
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What does the term 'horsepower' measure?
- How big the engine is
- The engine's power output, defined as the rate of doing work; specifically, 1 horsepower = 550 foot-pounds per second = 745.7 watts ✓
- How much fuel is in the tank
- How heavy the car is
Horsepower (HP): unit of POWER, originally defined by James Watt in the late 1700s to compare steam engine output to draft horses. He calculated that a mill horse could do 33,000 foot-pounds of work per minute (lift 33,000 lbs one foot in one minute), so 1 HP = 33,000 ft-lbs/min = 550 ft-lbs/second …
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If a car has trouble starting in cold weather, which is the LEAST likely cause?
- Weak or old battery
- Air conditioning system failure ✓
- Thicker engine oil (high viscosity) at cold temperatures
- Reduced fuel volatility
Cold-start problems can come from many sources, but A/C failure is NOT among them — A/C is for cooling the cabin, has nothing to do with starting. Cold weather affects starting in several ways: (1) BATTERY CHEMISTRY slows in cold — chemical reactions producing current are temperature-dependent; at 0…
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In an engine, what is 'top dead center' (TDC)?
- When the engine is on top of the car
- The position of the piston at the highest point of its travel in the cylinder, where the piston momentarily stops before reversing direction; reference point for valve timing, ignition timing, and other measurements ✓
- When the engine is dead and won't start
- The bottom of the cylinder
Top Dead Center (TDC): the position of a piston at the highest point in the cylinder, where it momentarily stops before reversing direction downward. The volume in the cylinder is at its MINIMUM at TDC (combustion chamber volume). Bottom Dead Center (BDC): the lowest piston position; volume at MAXIM…
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What is the difference between front-wheel drive (FWD), rear-wheel drive (RWD), and all-wheel drive (AWD)?
- All vehicles drive all wheels
- FWD powers only the front wheels (most economy cars); RWD powers only the rear wheels (sports cars, trucks); AWD powers all four wheels through differentials and a transfer case ✓
- These terms have no real meaning
- Only luxury cars have any of these features
Drive systems: (1) FRONT-WHEEL DRIVE (FWD) — engine drives only front wheels; usually mounted transversely (sideways); engine + transmission combined in TRANSAXLE (combined transmission and differential); driveshafts (CV axles) connect transaxle to front wheels. PROS: more interior space (no drivesh…
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What is the purpose of the radiator's pressure cap?
- Just decoration
- Pressurizes the cooling system (typically 15 psi), which raises the boiling point of coolant; also has a valve that allows coolant to flow to/from the overflow reservoir as it expands and contracts with temperature ✓
- Holds the radiator in place
- Cools the radiator
Radiator pressure cap: critical component that pressurizes the closed cooling system. Functions: (1) PRESSURIZES the system — typically 13-17 psi above atmospheric pressure (varies by vehicle); rating stamped on cap; (2) RAISES BOILING POINT of coolant — each 1 psi of pressure raises water's boiling…
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What is the function of the timing belt or timing chain?
- Holds the engine to the frame
- Synchronizes the rotation of the crankshaft and camshaft(s), ensuring the valves open and close at the correct times relative to the pistons; failure can cause catastrophic engine damage in interference engines ✓
- Drives the alternator
- Pumps fuel
Timing belt or timing chain: synchronizes crankshaft (which drives pistons) with camshaft (which operates valves); ensures valves open and close at correct points in the engine cycle. Crankshaft to camshaft ratio is 2:1 (crank rotates twice for each cam rotation), since cam controls a complete 4-str…
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What does a thermostat regulate in a vehicle's cooling system?
- Fuel flow
- Engine temperature ✓
- Oil pressure
- Battery voltage
The thermostat regulates coolant flow to maintain optimal engine operating temperature — it opens when the engine reaches operating temp to allow coolant to flow through the radiator.
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What type of brakes use fluid pressure to squeeze pads against a rotor?
- Drum brakes
- Disc brakes ✓
- Air brakes
- Regenerative brakes
Disc brakes use hydraulic fluid pressure to push brake calipers/pads against a rotating disc (rotor), creating friction to slow the vehicle.
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What is the function of the alternator in a vehicle?
- Starts the engine
- Charges the battery and powers electrical systems while running ✓
- Regulates fuel injection
- Controls the transmission
The alternator converts mechanical energy (from the engine belt) into electrical energy, charging the battery and supplying power to vehicle electronics while the engine runs.
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What does 'MPG' stand for?
- Miles per gear
- Motor power gauge
- Miles per gallon ✓
- Maximum power generated
MPG = Miles Per Gallon, the measure of fuel economy — how many miles a vehicle travels on one gallon of fuel.
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Which component converts fuel vapor and air into the combustible mixture in an older carbureted engine?
- Fuel injector
- Carburetor ✓
- Throttle body
- Intake manifold
The carburetor mixes air and fuel in the proper ratio for combustion in older engines. Modern engines use fuel injection instead, which more precisely controls fuel delivery.
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What is the purpose of the catalytic converter in a vehicle's exhaust system?
- Increases engine power
- Reduces harmful exhaust emissions by converting carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful gases (CO2, H2O, N2) ✓
- Improves fuel mileage
- Reduces engine noise
The CATALYTIC CONVERTER uses platinum, palladium, and rhodium catalysts to convert three major pollutants: Carbon Monoxide (CO) → Carbon Dioxide (CO2); Unburned Hydrocarbons (HC) → CO2 + H2O; Nitrogen Oxides (NOx) → Nitrogen (N2) + O2. Required on all US vehicles since 1975. Damage signs: rattling (…
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What is the purpose of the brake master cylinder?
- Stores brake fluid permanently
- Converts mechanical force from the brake pedal into hydraulic pressure that is transmitted to the wheel cylinders or brake calipers ✓
- Generates the heat that slows the vehicle
- Only applies the parking brake
The MASTER CYLINDER is the heart of the hydraulic brake system. When the driver presses the brake pedal, the pedal pushrod pushes a piston inside the master cylinder — this pressurises brake fluid, which transmits force through the brake lines to the wheel cylinders (drum brakes) or calipers (disc b…
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What does the acronym AWD stand for and how does it differ from 4WD?
- Automatic Wheel Drive; they are the same thing
- All-Wheel Drive — power is distributed to all four wheels automatically and continuously by the drivetrain computer; 4WD (Four-Wheel Drive) typically requires manual engagement and is designed for off-road use with low-range gearing ✓
- Advanced Wheel Distribution; 4WD uses rear wheels only
- They are identical systems with different marketing names
AWD: Automatically and continuously sends power to all four wheels; drivetrain computer varies distribution based on traction conditions; designed for on-road use in slippery conditions (rain, snow); most crossovers and SUVs use AWD. 4WD (4×4): Typically driver-engaged (2H/4H/4L selector); adds a tr…
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What warning should a driver take seriously if the oil pressure warning light comes on while driving?
- It is a minor issue that can wait until the next service
- Stop safely as soon as possible and turn off the engine — low oil pressure means the engine's moving parts may not be receiving adequate lubrication; driving even a short distance can cause severe engine damage or seizure ✓
- It means the car needs an oil change soon
- It only matters at highway speeds
OIL PRESSURE WARNING LIGHT = STOP IMMEDIATELY. This is one of the most serious warning lights. Oil lubricates every moving metal surface in the engine — bearings, camshaft, crankshaft, pistons. Without adequate pressure: metal contacts metal; temperature rises dramatically within seconds; permanent …
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What is a 'timing belt' and what happens if it breaks while the engine is running?
- It improves fuel economy; nothing major happens if it breaks
- The timing belt synchronises the rotation of the crankshaft and camshaft(s) to ensure valves open and close at the correct moment in the engine cycle; if it breaks on an interference engine, the pistons and valves collide, causing immediate and severe engine damage ✓
- It connects the alternator to the engine; its failure only affects battery charging
- It is only found on diesel engines
TIMING BELT (or timing chain) maintains the precise synchronisation between: CRANKSHAFT (controls piston movement) and CAMSHAFT (controls valve opening/closing). INTERFERENCE vs NON-INTERFERENCE ENGINE: In an interference engine, the piston and open valve occupy the same space at different moments —…
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In a four-stroke engine, what are the four strokes in order?
- Intake, power, compression, exhaust
- Intake, compression, power, exhaust ✓
- Compression, intake, exhaust, power
- Power, exhaust, intake, compression
The four strokes in order are: INTAKE (piston moves down, drawing in air/fuel), COMPRESSION (piston moves up, compressing the mixture), POWER (spark ignites the mixture, forcing the piston down — this produces power), and EXHAUST (piston moves up, pushing out burned gases). ASVAB Auto Information te…
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What is the main function of the alternator in a vehicle?
- To start the engine
- To generate electrical power and charge the battery while the engine runs ✓
- To cool the engine
- To filter the oil
The ALTERNATOR generates electrical power and CHARGES THE BATTERY while the engine runs, supplying electricity to the vehicle's systems. ASVAB Auto Information tests vehicle systems. The STARTER motor cranks the engine to start it (using battery power); the ALTERNATOR then takes over, producing elec…
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What is the purpose of engine oil?
- To cool the radiator
- To lubricate moving engine parts, reduce friction, and help cool and clean the engine ✓
- To power the spark plugs
- To inflate the tires
ENGINE OIL LUBRICATES moving engine parts, REDUCING FRICTION and wear; it also helps COOL and CLEAN the engine (carrying away heat and contaminants). ASVAB Auto Information tests the lubrication system. Without oil, metal parts would grind together, overheat, and seize. Oil must be changed periodica…
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What does the cooling system (radiator and coolant) do in a vehicle?
- Lubricates the engine
- Removes excess heat from the engine to prevent overheating ✓
- Generates electricity
- Provides fuel to the engine
The COOLING SYSTEM removes excess HEAT from the engine to prevent OVERHEATING. ASVAB Auto Information tests the cooling system. COOLANT (antifreeze mixed with water) circulates through the engine, absorbing heat, then flows to the RADIATOR where airflow cools it; the WATER PUMP circulates the coolan…
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What component ignites the air-fuel mixture in a gasoline engine?
- The fuel injector
- The spark plug ✓
- The piston
- The muffler
The SPARK PLUG ignites the air-fuel mixture in a gasoline engine, creating the spark that causes combustion during the power stroke. ASVAB Auto Information tests ignition. The spark plug receives high voltage (from the ignition coil) and produces a spark across its gap, igniting the compressed air-f…
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What is the purpose of the transmission in a vehicle?
- To store fuel
- To transfer engine power to the wheels and change gear ratios for different speeds ✓
- To cool the engine
- To filter air
The TRANSMISSION transfers engine power to the wheels and CHANGES GEAR RATIOS to match engine speed to driving conditions (low gears for starting/climbing with more torque; high gears for cruising at speed). ASVAB Auto Information tests the drivetrain. MANUAL transmissions use a clutch and driver-se…
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What is the function of the brake system's master cylinder?
- To pump fuel
- To convert the force from the brake pedal into hydraulic pressure that activates the brakes ✓
- To charge the battery
- To turn the wheels
The MASTER CYLINDER converts the force from the brake pedal into HYDRAULIC PRESSURE, which is transmitted through brake lines to activate the brakes at each wheel. ASVAB Auto Information tests the brake system. When you press the pedal, the master cylinder pushes brake fluid through the lines to the…
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What does the term 'RPM' measure in an engine?
- Fuel level
- Revolutions per minute (how fast the engine's crankshaft is turning) ✓
- Tire pressure
- Oil temperature
RPM stands for REVOLUTIONS PER MINUTE — it measures how fast the engine's CRANKSHAFT is turning (engine speed). ASVAB Auto Information tests engine terminology. The TACHOMETER displays RPM. Higher RPM means the engine is working harder/faster; idling is low RPM, and there's a 'redline' maximum RPM t…
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What is the purpose of a vehicle's catalytic converter?
- To increase horsepower
- To reduce harmful emissions by converting toxic exhaust gases into less harmful substances ✓
- To cool the engine
- To store electricity
The CATALYTIC CONVERTER reduces harmful EMISSIONS by converting toxic exhaust gases (carbon monoxide, hydrocarbons, nitrogen oxides) into less harmful substances (carbon dioxide, water, nitrogen) through catalytic reactions. ASVAB Auto Information tests emissions/exhaust systems. It's part of the ex…
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What does the clutch do in a manual transmission vehicle?
- Applies the brakes
- Engages and disengages the engine from the transmission, allowing gear changes ✓
- Steers the vehicle
- Charges the battery
The CLUTCH engages and disengages the engine from the transmission, allowing the driver to CHANGE GEARS smoothly and to stop without stalling. ASVAB Auto Information tests the manual drivetrain. Pressing the clutch pedal DISENGAGES the engine from the transmission (so you can shift gears or stop); r…
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What is the recommended action if the engine temperature gauge reads in the red (overheating) zone?
- Speed up to cool it faster
- Safely pull over, turn off the engine, and let it cool to prevent serious engine damage ✓
- Ignore it and keep driving
- Add more fuel
If the temperature gauge reads in the RED/overheating zone, the recommended action is to SAFELY PULL OVER, turn off the engine, and let it COOL — continuing to drive an overheating engine can cause severe damage (warped cylinder head, blown head gasket, seized engine). ASVAB Auto Information tests b…
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What is the purpose of the vehicle's battery?
- To cool the engine
- To store electrical energy, primarily to start the engine and power electronics when the engine is off ✓
- To lubricate the engine
- To filter fuel
The BATTERY stores electrical energy — primarily to provide the power to START the engine (running the starter motor) and to power electronics (lights, radio) when the engine is off. ASVAB Auto Information tests the electrical system. Once the engine runs, the ALTERNATOR takes over powering the car …
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What is the function of the vehicle's differential?
- To start the engine
- To allow the drive wheels to rotate at different speeds (such as when turning) while transmitting power ✓
- To cool the brakes
- To pump fuel
The DIFFERENTIAL allows the drive wheels to rotate at DIFFERENT SPEEDS — necessary when TURNING, because the outer wheel travels farther than the inner wheel — while still transmitting power from the driveshaft to the wheels. ASVAB Auto Information tests the drivetrain. Without a differential, the w…
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Which tool is specifically designed to measure the gap of a spark plug?
- A torque wrench
- A feeler gauge (gap gauge) ✓
- A socket wrench
- A screwdriver
A FEELER GAUGE (or spark plug gap gauge) is used to measure the GAP of a spark plug (the small space between the center and ground electrodes). ASVAB Auto Information (overlapping with Shop) tests tool knowledge. The correct gap is important for proper spark and engine performance. A TORQUE WRENCH m…
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What is the purpose of the vehicle's suspension system (springs, shock absorbers)?
- To power the wheels
- To absorb road shocks and bumps, providing a smoother ride and keeping the tires in contact with the road ✓
- To ignite the fuel
- To charge the battery
The SUSPENSION SYSTEM (springs, shock absorbers/struts) ABSORBS road shocks and bumps, providing a smoother ride and keeping the TIRES IN CONTACT with the road for control and handling. ASVAB Auto Information tests the suspension/chassis. SPRINGS absorb impacts; SHOCK ABSORBERS (dampers) control spr…
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In a four-stroke engine, what are the four strokes in the correct order?
- Intake, compression, power, exhaust ✓
- Compression, intake, exhaust, power
- Power, exhaust, intake, compression
- Intake, power, compression, exhaust
The four strokes of a four-stroke engine, in order, are: Intake (the piston moves down, drawing in the air-fuel mixture), Compression (the piston moves up, compressing the mixture), Power (the spark ignites the mixture, forcing the piston down), and Exhaust (the piston moves up, pushing out the burn…
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What is the function of the spark plug in a gasoline engine?
- To pump fuel
- To ignite the compressed air-fuel mixture in the cylinder ✓
- To filter the oil
- To cool the engine
The spark plug ignites the compressed air-fuel mixture in the combustion chamber by creating an electric spark at precisely the right moment. This ignition causes the controlled explosion that drives the piston down during the power stroke. Spark plugs are part of the ignition system in gasoline eng…
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What does a fuel injector do?
- Stores fuel
- Sprays a precise amount of fuel into the engine's intake or cylinder ✓
- Cools the fuel
- Filters air
A fuel injector sprays a precise, metered amount of fuel into the engine — into the intake port or directly into the cylinder — where it mixes with air for combustion. Modern engines use electronic fuel injection (EFI) controlled by the engine computer, which has largely replaced the older carbureto…
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What is the purpose of the transmission in a vehicle?
- To store fuel
- To transfer engine power to the wheels and allow gear changes for different speeds ✓
- To cool the engine
- To steer the vehicle
The transmission transfers power from the engine to the drive wheels and uses different gear ratios to match engine speed to driving conditions — lower gears for starting and climbing (more torque), higher gears for cruising (more speed, lower engine RPM). A manual transmission uses a clutch and dri…
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What is the purpose of the clutch in a manual transmission vehicle?
- To apply the brakes
- To engage and disengage the engine from the transmission so gears can be changed ✓
- To inflate the tires
- To charge the battery
The clutch connects and disconnects the engine from the transmission. Pressing the clutch pedal disengages the engine from the drivetrain, allowing the driver to change gears or come to a stop without stalling; releasing it re-engages the engine to the transmission to transfer power. The clutch work…
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How do disc brakes slow a vehicle?
- By inflating a cushion
- By squeezing brake pads against a rotating disc (rotor) to create friction ✓
- By reversing the engine
- By cooling the tires
Disc brakes slow a vehicle by using a caliper to squeeze brake pads against both sides of a spinning metal disc called a rotor, which is attached to the wheel. The friction converts the vehicle's kinetic energy into heat, slowing the wheel. Hydraulic pressure from the brake fluid, created when you p…
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What is the main purpose of a vehicle's suspension system (shocks and struts)?
- To power the wheels
- To absorb road bumps and keep the tires in contact with the road for a smooth, controlled ride ✓
- To store fuel
- To steer the vehicle by itself
The suspension system — including springs, shock absorbers, and struts — absorbs bumps and vibrations from the road, cushions the ride, and keeps the tires in firm contact with the road surface for traction, handling, and braking. Shock absorbers (shocks) dampen the bouncing of the springs, while st…
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What is the primary function of engine oil?
- To fuel the engine
- To lubricate moving parts, reduce friction and wear, and help carry away heat ✓
- To inflate the tires
- To clean the windshield
Engine oil lubricates the engine's moving parts to reduce friction and wear, and it also helps cool components by carrying away heat, cleans by suspending contaminants, and helps seal gaps. Without adequate oil, metal parts would grind together, overheat, and quickly fail. The oil is circulated by t…
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What is the purpose of the radiator in a vehicle's cooling system?
- To generate electricity
- To dissipate heat from the engine coolant into the air ✓
- To store extra fuel
- To filter engine oil
The radiator dissipates heat from the engine coolant (antifreeze) into the surrounding air. Hot coolant from the engine flows through the radiator's thin tubes and fins, where airflow — aided by the cooling fan — removes the heat before the cooled coolant returns to circulate through the engine agai…
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What component recharges the vehicle's battery and powers electrical systems while the engine runs?
- The starter
- The alternator ✓
- The radiator
- The muffler
The alternator generates electricity while the engine runs, recharging the battery and powering the vehicle's electrical systems (lights, ignition, accessories). It is driven by a belt from the engine and converts mechanical energy into electrical energy. The battery, by contrast, provides the initi…
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What does engine displacement measure?
- The weight of the engine
- The total volume swept by all the pistons in the cylinders ✓
- The number of spark plugs
- The oil capacity
Engine displacement is the total volume swept by all the pistons moving inside the cylinders during one stroke, usually expressed in liters or cubic centimeters (cc). It is a basic measure of an engine's size and a rough indicator of its potential power and air-fuel intake — a larger displacement ge…
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What is the purpose of the catalytic converter in the exhaust system?
- To increase engine power
- To reduce harmful emissions by converting toxic exhaust gases into less harmful substances ✓
- To cool the engine
- To store fuel
The catalytic converter is part of the exhaust system that reduces harmful emissions. It uses precious-metal catalysts to convert toxic gases — carbon monoxide, unburned hydrocarbons, and nitrogen oxides — into less harmful substances like carbon dioxide, water vapor, and nitrogen before they leave …
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What is the function of the differential in a vehicle's drivetrain?
- To ignite the fuel
- To allow the drive wheels to rotate at different speeds, especially when turning ✓
- To filter the air
- To charge the battery
The differential allows the drive wheels to turn at different speeds, which is necessary when a vehicle goes around a corner — the outside wheel travels a longer path and must rotate faster than the inside wheel. The differential splits engine torque between the wheels while permitting this speed di…
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What does ABS (anti-lock braking system) do during hard braking?
- Makes the car stop instantly
- Prevents the wheels from locking up so the driver can keep steering control ✓
- Increases engine power
- Turns off the brakes
An anti-lock braking system (ABS) rapidly pulses the brakes to prevent the wheels from locking up during hard or emergency braking. Locked wheels skid and lose steering control; by keeping the wheels rotating, ABS lets the driver continue to steer while braking hard and helps maintain traction, espe…
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What is the difference between how a gasoline engine and a diesel engine ignite their fuel?
- They ignite identically
- A gasoline engine uses a spark plug to ignite the mixture; a diesel engine ignites fuel by the heat of high compression, with no spark plug ✓
- Diesel uses spark plugs, gasoline uses compression
- Neither uses combustion
A gasoline engine uses a spark plug to ignite the compressed air-fuel mixture at the right moment. A diesel engine has no spark plugs; instead it compresses air to a very high pressure, which makes it hot enough that injected diesel fuel ignites on contact (compression ignition). Diesel engines run …