Automotive Information

The Automotive Information subtest of the ASVAB measures your understanding of how vehicles work, covering everything from engines and transmissions to electrical systems and brakes. This section is important for anyone considering a military career in vehicle maintenance, mechanics, or engineering fields.

On the CAT-ASVAB, the Auto and Shop Information section is divided into separate Auto and Shop subtests, with 11 automotive questions in 7 minutes. On the paper version, the two subjects are combined, with 25 total questions in 11 minutes.

1. Basic Automotive Knowledge

Understanding a vehicle’s structural framework and core mechanical components is essential in automotive knowledge.

Chassis & Frame

The chassis is the main structural framework of a vehicle, supporting mechanical components, passengers, and cargo.
There are two primary types of construction:

  • Body-on-Frame – The body and chassis are separate; common in trucks and SUVs.
  • Unibody Construction – The body and chassis are integrated into a single structure; common in modern passenger cars.

Internal Combustion Engine

The engine converts chemical energy (fuel) into mechanical energy through combustion. The four-stroke cycle describes how this occurs:

  1. Intake – The air-fuel mixture enters the cylinder.
  2. Compression – The piston moves up, compressing the mixture to generate heat.
  3. Combustion – The spark plug ignites the mixture, causing an explosion that drives the piston down.
  4. Exhaust – The spent gases exit through the exhaust valve.

Carburetors vs. Fuel Injectors

  • Carburetors (found in older vehicles) mechanically mix fuel and air.
  • Fuel Injectors (used in modern vehicles) electronically control the fuel-air mixture, improving efficiency.

Common Engine Components

  • Pistons & Rings – Move inside the cylinder to create motion.
  • Crankshaft – Converts the up-and-down piston motion into rotary motion.
  • Camshaft – Controls the opening/closing of the intake and exhaust valves.
  • Cylinder Head & Combustion Chamber – The location where the fuel combusts.

Engine Configurations

Engines come in different cylinder arrangements and cylinder counts:

  • Arrangements:
    • Inline – Cylinders are in a straight row (common in 4-cylinder engines).
    • V-Type – Cylinders are arranged in a “V” shape (e.g., V6, V8).
    • Horizontally Opposed – Cylinders lie flat and oppose each other (common in Subaru & Porsche engines).
  • Cylinder Count: More cylinders provide more power but reduce fuel efficiency. Common setups: 4, 6, 8 cylinders.

Fuel Types & Efficiency

  • Gasoline (Octane Ratings):
    • Regular (87) – Used in most vehicles.
    • Midgrade (89) – Offers better performance.
    • Premium (91-93) – Required for high-performance engines.
  • Diesel Engines – More powerful and fuel-efficient, using compression ignition instead of a spark plug.
  • Electric Vehicles (EVs) – Use batteries instead of combustion.
  • Hybrid Vehicles – Combine gasoline engines with electric motors to improve fuel efficiency.

2. Automotive Electrical & Ignition Systems

A vehicle’s electrical system powers everything from the ignition to the lights.

Key Components

  • Battery – Stores and supplies electrical energy to start the engine.
  • Starter Motor – Uses the battery’s power to crank the engine.
  • Alternator – Recharges the battery while the engine is running.

Ignition System

The ignition system provides high-voltage current to the spark plugs, igniting the air-fuel mixture.

  • Older systems used distributors to send current.
  • Modern vehicles use computer-controlled electronic ignition, making them more efficient and reliable.

3. Cooling & Lubrication Systems

Engines generate heat and require cooling and lubrication to prevent damage.

Cooling System

  • Liquid-cooled engines use coolant that circulates through the radiator and water pump to absorb heat.

Lubrication System

  • Reduces friction and heat in moving engine components.
  • Main components:
    • Oil Pump – Circulates oil throughout the engine.
    • Oil Filter – Removes dirt and contaminants.
    • Oil Pan – Stores oil.
    • Pickup Tube & Screen – Draws oil from the pan and filters debris.

4. Exhaust & Emissions Systems

Vehicles release exhaust gases that must be controlled to reduce pollution.

Exhaust System Components

  • Exhaust Manifold – Collects gases from the engine’s cylinders.
  • Catalytic Converter – Converts harmful gases (carbon monoxide) into less toxic emissions.
  • Muffler – Reduces engine noise.
  • Tailpipe – Releases gases into the air.

Emissions Control Systems

  • Positive Crankcase Ventilation (PCV) – Reuses unspent fuel to reduce emissions.
  • Exhaust Gas Recirculation (EGR) – Reduces nitrogen oxide emissions.

5. Drive Systems & Transmission

The drivetrain transfers power from the engine to the wheels.

Drivetrain Types

  • Rear-Wheel Drive (RWD) – Power goes to the rear wheels (used in trucks and sports cars).
  • Front-Wheel Drive (FWD) – Power goes to the front wheels (common in most cars).
  • All-Wheel Drive (AWD)/Four-Wheel Drive (4WD) – Power is distributed to all wheels for better traction.

Transmission Types

  • Manual Transmission – Requires the driver to shift gears using a clutch.
  • Automatic Transmission – Uses a torque converter to shift gears automatically.

6. Suspension & Steering Systems

These systems keep the ride smooth and allow the driver to control the vehicle.

Suspension System

  • Struts & Shock Absorbers – Reduce bumps and jolts.
  • Springs – Hold the chassis up and adapt to road surfaces.
  • Control Arms & Tie Rods – Keep the wheels aligned.

Steering Systems

  • Rack-and-Pinion – Common in modern vehicles.
  • Pitman Arm Steering – Found in older and heavy-duty vehicles.

7. Brake Systems & ABS (Antilock Brakes)

Types of Brakes

  • Drum Brakes – Use brake shoes that press against a rotating drum.
  • Disc Brakes – Use brake pads and calipers that press against a rotor (more effective than drum brakes).

Antilock Braking System (ABS)

  • Prevents wheels from locking up during emergency braking, allowing better control.

8. Summary of Key Automotive Information Topics

Category Key Concepts
Chassis & Frame Vehicle structure, unibody vs. body-on-frame construction.
Engine Basics Four-stroke cycle (intake, compression, combustion, exhaust).
Fuel Systems Carburetors (old) vs. Fuel Injectors (modern).
Cylinder Configurations Inline, V-type, Horizontally Opposed.
Fuel Types Gasoline, Diesel, Electric, Hybrid.
Electrical & Ignition Battery, Starter, Alternator, Spark Plugs.
Cooling & Lubrication Radiator, Water Pump, Oil System.
Exhaust & Emissions Catalytic Converter, PCV, EGR, Muffler.
Drive Systems RWD, FWD, AWD/4WD, Manual vs. Automatic Transmission.
Suspension & Steering Shocks, Struts, Springs, Control Arms, Tie Rods.
Brake Systems Drum vs. Disc Brakes, ABS.

 

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