Vehicle Systems: Practice Questions & Explanations

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 electricity to run the car and recharge the battery. If the alternator fails, the car runs on battery alone until it dies. Knowing the alternator charges the battery and powers electrical systems (vs the starter that starts the engine) is commonly tested.

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 periodically because it degrades and collects contaminants. The OIL FILTER removes particles. Knowing oil's primary job (lubrication/reducing friction, plus cooling and cleaning) is commonly tested auto knowledge.

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 coolant, and the THERMOSTAT regulates temperature. Overheating can cause severe engine damage. Knowing the cooling system's job (removing heat to prevent overheating) and its main components (radiator, coolant, water pump, thermostat) is commonly tested.

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-fuel mixture. (DIESEL engines have no spark plugs — they ignite fuel by compression heat.) Other parts: FUEL INJECTOR (delivers fuel); PISTON (moves in the cylinder). Knowing the spark plug ignites the mixture in a gas engine is commonly tested.

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 wheel cylinders/calipers, which press the brake pads/shoes against the rotors/drums to slow the car (using Pascal's principle of hydraulics). Knowing the master cylinder's role in the hydraulic brake system is commonly tested.

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); releasing it re-engages the connection. The clutch uses friction plates. Automatic transmissions use a torque converter instead of a clutch pedal. Knowing the clutch's role (connecting/disconnecting engine and transmission for shifting) is commonly tested.

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 and recharging the battery. A typical car battery is 12 volts. A dead battery is a common cause of no-start. Knowing the battery's purpose (starting the engine, powering electronics, working with the alternator) is commonly tested.

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 wheels would be forced to turn at the same speed, causing tire scrub and difficult handling in turns. It's part of the axle assembly. Knowing the differential's purpose (allowing wheels to turn at different speeds while delivering power) is commonly tested.

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 spring bounce; together they smooth the ride and maintain traction and stability. A worn suspension causes a rough, bouncy ride and poor handling. Knowing the suspension's purpose (absorbing shocks, smooth ride, tire-road contact) is commonly tested.