ASVAB Auto Information Practice Test

25 practice questions

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1. Question 1 of 25Medium

   What is the primary role of the main oil galleries inside an engine block?

   1. AA. To reserve excess oil during sudden cornering maneuvers
   2. BB. To collect drainback oil and route it to the exhaust system
   3. CC. To distribute pressurized oil to internal engine components
   4. DD. To vent crankcase blow-by gases into the intake manifold
   Show answer to question 1

   Answer: C. To distribute pressurized oil to internal engine components

   Oil galleries are precision-drilled passages and channels inside the engine block and cylinder head that carry pressurized oil from the pump and filter to the crankshaft bearings, camshafts, and lifters. Crankcase fumes are routed by the positive crankcase ventilation system rather than oil galleries. Oil is never intentionally routed to the exhaust system.

2. Question 2 of 25Medium

   In a four-stroke engine, at what rotational speed does the camshaft turn relative to the crankshaft?

   1. AA. Half the speed of the crankshaft
   2. BB. One-quarter the speed of the crankshaft
   3. CC. The same speed as the crankshaft
   4. DD. Twice the speed of the crankshaft
   Show answer to question 2

   Answer: A. Half the speed of the crankshaft

   Each valve opens exactly once during the four-stroke cycle, which takes two full revolutions of the crankshaft. Therefore, the camshaft must complete one revolution for every two revolutions of the crankshaft, making it rotate at half the crankshaft speed. Rotating at twice the crankshaft speed would cause the valves to open four times per engine cycle.

3. Question 3 of 25Easy

   Which gasket is installed between the cylinder head and the engine block to contain combustion pressure, coolant, and engine oil?

   1. AA. Valve cover gasket
   2. BB. Intake manifold gasket
   3. CC. Exhaust flange gasket
   4. DD. Head gasket
   Show answer to question 3

   Answer: D. Head gasket

   The head gasket seals the high pressure generated during combustion while separating internal passages for coolant and oil traveling between the engine block and the cylinder head. A valve cover gasket seals the top of the cylinder head to retain splash oil but is not exposed to combustion pressure or coolant.

4. Question 4 of 25Medium

   How does a torsion bar spring provide spring action?

   1. AA. It twists along its length as the suspension moves
   2. BB. It traps compressed air in a rubber chamber
   3. CC. It bends a stack of flat steel leaves
   4. DD. It compresses a coil of wire inside a housing
   Show answer to question 4

   Answer: A. It twists along its length as the suspension moves

   A torsion bar is anchored at one end and twists as the suspension moves, and the bar's resistance to twisting acts as the spring. Compressing a coil of wire describes a coil spring, not a torsion bar.

5. Question 5 of 25Hard

   What is the main function of a flexible pipe installed between the exhaust manifold and the rest of the exhaust system?

   1. AA. Introducing fresh outside air to cool the catalytic converter housing
   2. BB. Allowing hot exhaust gases to expand and decrease backpressure
   3. CC. Absorbing engine movement to prevent rigid exhaust pipes from cracking
   4. DD. Providing an expansion joint to collect condensed water from the system
   Show answer to question 5

   Answer: C. Absorbing engine movement to prevent rigid exhaust pipes from cracking

   Because the engine rocks on its rubber mounts during acceleration and gear shifts, a flexible pipe section absorbs these torsional movements to protect the rigid exhaust pipes and manifolds from stress fractures. Introducing outside air or collecting water condensation are not functions of the flex pipe.

6. Question 6 of 25Medium

   A master cylinder piston has a smaller diameter than a caliper piston. What effect does this have when the brakes are applied?

   1. AA. It increases force at the caliper but requires more pedal travel.
   2. BB. It increases force at the caliper and shortens pedal travel.
   3. CC. It decreases force at the caliper but shortens pedal travel.
   4. DD. It leaves force unchanged while reducing pedal travel.
   Show answer to question 6

   Answer: A. It increases force at the caliper but requires more pedal travel.

   A smaller master cylinder piston creates higher pressure for a given pedal force, and that pressure acting on the larger caliper piston produces more clamping force. The trade-off is that the smaller piston must move farther to displace enough fluid, so pedal travel increases.

7. Question 7 of 25Hard

   What action does the engine control module take when a piezoelectric knock sensor detects engine detonation?

   1. AA. It opens the exhaust gas recirculation valve fully to starve the cylinders
   2. BB. It cuts power to the fuel pump until the engine cools down completely
   3. CC. It advances the ignition timing to burn the fuel charge more rapidly
   4. DD. It retards the ignition timing to prevent severe engine damage
   Show answer to question 7

   Answer: D. It retards the ignition timing to prevent severe engine damage

   When a knock sensor detects the vibrations caused by abnormal combustion or pinging, the control module retards ignition timing to reduce cylinder peak pressures and stop the knock. Advancing ignition timing would worsen the detonation and increase the risk of catastrophic piston or valve damage.

8. Question 8 of 25Easy

   Which engine component bolts to the top of the cylinder block and contains the combustion chambers, valve seats, and spark plug openings?

   1. AA. Valve cover
   2. BB. Oil pan
   3. CC. Intake manifold
   4. DD. Cylinder head
   Show answer to question 8

   Answer: D. Cylinder head

   The cylinder head closes off the top of the cylinders and carries the combustion chambers, valves, and spark plug holes. A valve cover only shields the valvetrain on top of the head, and the oil pan closes the bottom of the block.

9. Question 9 of 25Medium

   What causes the phenomenon known as turbo lag?

   1. AA. The time required for exhaust gas volume and turbine rotational speed to build
   2. BB. The slippage of the drive belt under sudden engine acceleration
   3. CC. The delay in fuel delivery caused by low intake manifold pressure
   4. DD. The thermal expansion of the compressor housing during hard acceleration
   Show answer to question 9

   Answer: A. The time required for exhaust gas volume and turbine rotational speed to build

   Turbo lag is the brief hesitation between pressing the accelerator and feeling boost, caused by the rotational inertia of the turbine and the time needed to generate sufficient exhaust pressure. Drive belt slippage occurs in belt-driven supercharger setups, not turbochargers.

10. Question 10 of 25Medium

    Why are diesel engine blocks typically heavier and more robust than gasoline engine blocks of similar displacement?

    1. AA. They house an additional set of camshafts for fuel pressurization
    2. BB. They use solid cast lead rather than cast iron or aluminum
    3. CC. They require thicker cylinder walls to withstand higher combustion pressures
    4. DD. They must hold double the volume of engine coolant to prevent overheating
    Show answer to question 10

    Answer: C. They require thicker cylinder walls to withstand higher combustion pressures

    Diesel engines operate at much higher compression ratios and peak cylinder pressures than gasoline engines, requiring stronger, thicker cylinder walls and structural reinforcement to avoid structural failure. Engine blocks are constructed from cast iron or high-strength aluminum alloys, not lead.

11. Question 11 of 25Hard

    A technician measures an unexpected 1.5-volt drop across a ground wire connecting a headlight to the vehicle chassis. What does this measurement indicate?

    1. AA. The headlight bulb is drawing insufficient amperage from the battery
    2. BB. The vehicle alternator is producing an unsafe overvoltage condition
    3. CC. The ground circuit has excessive resistance that should be repaired
    4. DD. The ground wire gauge is significantly too large for the circuit load
    Show answer to question 11

    Answer: C. The ground circuit has excessive resistance that should be repaired

    A properly functioning ground circuit should have almost zero resistance, resulting in a negligible voltage drop, typically under 0.1 to 0.2 volts. A 1.5-volt drop indicates unwanted resistance caused by corrosion, a loose connection, or damaged wiring, which deprives the headlight of full operational voltage. A wire that is too large would actually lower resistance and reduce voltage drop rather than increase it.

12. Question 12 of 25Medium

    In a rear-wheel-drive vehicle, which part carries engine power from the transmission to the rear axle?

    1. AA. A transaxle
    2. BB. A driveshaft
    3. CC. A half shaft
    4. DD. A transfer case
    Show answer to question 12

    Answer: B. A driveshaft

    A driveshaft, also called a propeller shaft, carries torque from the transmission back to the rear differential, which splits it to the rear wheels. A half shaft is a short axle at a driven wheel, and a transfer case is used on four-wheel-drive vehicles rather than a conventional rear-wheel-drive car.

13. Question 13 of 25Medium

    What tread wear pattern is most characteristic of a tire that has been run at too high an inflation pressure?

    1. AA. Even wear across the full tread width
    2. BB. A single bald spot on one sidewall
    3. CC. Wear concentrated in the center of the tread
    4. DD. Wear concentrated on both outer edges
    Show answer to question 13

    Answer: C. Wear concentrated in the center of the tread

    Overinflation bows the tread center outward, so the middle of the tread contacts the road hardest and wears faster. Wear on both outer edges is more typical of underinflation. Even wear generally indicates correct pressure and proper rotation.

14. Question 14 of 25Medium

    Which system uses a catalytic converter to reduce harmful gases in the exhaust?

    1. AA. Cooling system
    2. BB. Fuel system
    3. CC. Evaporative emission system
    4. DD. Exhaust system
    Show answer to question 14

    Answer: D. Exhaust system

    The exhaust system routes burned gases away from the engine, and the catalytic converter changes harmful gases into less harmful ones. The fuel system delivers fuel, while the evaporative emission system captures fuel vapors.

15. Question 15 of 25Medium

    A vehicle's steering wheel shakes at about 55 mph, and the shake fades below and above that speed. The tires show even wear. Which is the most likely cause?

    1. AA. The front toe is set too far in
    2. BB. One or both front wheels are out of balance
    3. CC. The caster is out of specification
    4. DD. The thrust angle is out of specification
    Show answer to question 15

    Answer: B. One or both front wheels are out of balance

    An unbalanced wheel creates a vibration that peaks at a particular road speed and fades away on either side of it. Misalignment such as wrong toe, caster or thrust angle produces a pull, an off-center steering wheel or uneven tire wear rather than a speed-specific shake.

16. Question 16 of 25Easy

    Which component provides heat to warm the passenger compartment in a typical liquid-cooled automobile?

    1. AA. Thermostat
    2. BB. Heater core
    3. CC. Water pump
    4. DD. Radiator
    Show answer to question 16

    Answer: B. Heater core

    The heater core acts as a small heat exchanger that circulates hot engine coolant so the blower fan can push warm air into the passenger compartment. While the radiator also cools the engine coolant, its purpose is to reject heat to the outside atmosphere rather than to warm the vehicle interior.

17. Question 17 of 25Medium

    Which section of a piston serves primarily to keep it from rocking or tilting inside the cylinder bore?

    1. AA. Piston skirt
    2. BB. Piston crown
    3. CC. Ring land
    4. DD. Pin boss
    Show answer to question 17

    Answer: A. Piston skirt

    The piston skirt is the cylindrical side area below the ring grooves that acts as a guide against the cylinder wall to maintain alignment and stop the piston from tilting. The piston crown is the top surface that directly faces the combustion chamber and bears combustion pressure.

18. Question 18 of 25Easy

    What is the primary safety purpose of an antilock braking system (ABS)?

    1. AA. To reduce the wear rate on the brake pads and rotors during sudden stops
    2. BB. To increase transmission engine braking power during downhill driving
    3. CC. To prevent wheels from skidding so the driver maintains steering control
    4. DD. To eliminate the need for regular brake fluid inspection and flushing
    Show answer to question 18

    Answer: C. To prevent wheels from skidding so the driver maintains steering control

    The primary purpose of an antilock braking system is to prevent wheel lockup during hard braking, which allows the driver to retain steering control. While ABS may shorten stopping distances on certain surfaces, it does not reduce friction lining wear or affect engine braking.

19. Question 19 of 25Easy

    Ignition timing is measured in degrees of crankshaft rotation relative to the piston reaching which position?

    1. AA. Top dead center
    2. BB. Exhaust valve overlap
    3. CC. Mid-stroke intake
    4. DD. Bottom dead center
    Show answer to question 19

    Answer: A. Top dead center

    Ignition timing indicates when the spark plug fires relative to the piston reaching top dead center (TDC) on the compression stroke. Bottom dead center refers to the lowest point of piston travel and is not used as the reference mark for ignition timing.

20. Question 20 of 25Hard

    In modern computer-controlled vehicles, what does a differential pressure feedback EGR (DPFE) sensor measure?

    1. AA. The temperature change across the catalytic converter
    2. BB. The electrical resistance across the EGR solenoid coil
    3. CC. The manifold vacuum level to determine throttle position
    4. DD. The pressure drop across a restriction to calculate exhaust gas flow
    Show answer to question 20

    Answer: D. The pressure drop across a restriction to calculate exhaust gas flow

    A DPFE sensor measures the pressure difference across a calibrated metering orifice in the EGR tube to determine the actual volume of exhaust gas flowing into the intake. Manifold vacuum is measured by a manifold absolute pressure (MAP) sensor rather than a DPFE sensor.

21. Question 21 of 25Easy

    Which engine accessory is driven by the crankshaft pulley to circulate engine coolant through the cooling system?

    1. AA. Power steering pump
    2. BB. Alternator
    3. CC. Air conditioning compressor
    4. DD. Water pump
    Show answer to question 21

    Answer: D. Water pump

    The water pump pulley is turned by an accessory drive belt connected to the crankshaft to circulate coolant between the engine block and radiator. While the alternator is also belt-driven, its primary job is generating electrical power rather than moving liquid through the cooling system.

22. Question 22 of 25Hard

    What symptom is most likely to occur if a diode in the alternator's rectifier fails in an open state?

    1. AA. Immediate reversal of the vehicle electrical system polarity
    2. BB. Reduced maximum output capacity and excessive AC ripple voltage
    3. CC. Excessive charging voltage that boils the battery electrolyte
    4. DD. Mechanical seizure of the alternator bearings and drive belt
    Show answer to question 22

    Answer: B. Reduced maximum output capacity and excessive AC ripple voltage

    An open diode drops one phase of rectification, which reduces total current capacity by roughly one-third and allows unwanted alternating current ripple into the DC electrical system. Abnormally high charging voltage that boils battery fluid is caused by a defective voltage regulator that stays full-fielded. Mechanical seizure results from bearing or hardware failure, not an open electrical diode.

23. Question 23 of 25Easy

    Which ignition system component transforms 12-volt battery power into thousands of volts needed to jump the spark plug gap?

    1. AA. Starter solenoid
    2. BB. Ignition coil
    3. CC. Alternator
    4. DD. Voltage regulator
    Show answer to question 23

    Answer: B. Ignition coil

    The ignition coil acts as a step-up transformer, taking low battery voltage and converting it into secondary high voltage to fire the spark plugs. The alternator generates electrical power to recharge the battery while the engine runs, but it does not step up voltage to ignite fuel.

24. Question 24 of 25Hard

    Why do manufacturers of modern passenger vehicles commonly specify low-viscosity oils such as 0W-20?

    1. AA. To extend crankcase capacity without adding supplementary cooling lines
    2. BB. To eliminate oil burning caused by worn valve stem seals
    3. CC. To lubricate tight internal clearances quickly and improve fuel efficiency
    4. DD. To compensate for wide bearing gaps in lightweight engine blocks
    Show answer to question 24

    Answer: C. To lubricate tight internal clearances quickly and improve fuel efficiency

    Modern engines feature tight machining tolerances and bearing clearances that require low-viscosity oil to achieve rapid lubrication while reducing parasitic drag to improve fuel economy. Higher viscosity oils create greater drag and may struggle to flow promptly through tight journal clearances upon startup.

25. Question 25 of 25Hard

    How does a vacuum-operated power valve determine when to supply extra fuel during heavy engine loads?

    1. AA. It closes when exhaust backpressure rises above engine idle levels
    2. BB. It opens when intake manifold vacuum drops below a calibrated level
    3. CC. It closes when intake air velocity reaches maximum speed
    4. DD. It opens when fuel bowl pressure exceeds atmospheric pressure
    Show answer to question 25

    Answer: B. It opens when intake manifold vacuum drops below a calibrated level

    Under heavy engine load or wide-open throttle, intake manifold vacuum drops significantly because the throttle plates are open. When vacuum drops below a specific spring tension, the power valve opens to supply additional fuel to the main metering system for maximum power and engine cooling. Bowl pressure is maintained near atmospheric pressure and does not trigger the power valve.

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