Battery
The battery stores electrical energy for starting and stabilizes voltage for the vehicle's electronics.
Provides high current to the starter and powers modules before the engine is running.Guide library
Parts and Systems
Learn what each part does, how it fails, and which symptoms it can cause.
Symptom first
Safety check
Likely causes
Mechanic notes
Starter Motor
The starter motor turns the engine fast enough for combustion to begin.
Uses battery power through a solenoid to crank the engine.Alternator
The alternator recharges the battery and powers the electrical system once the engine is running.
Converts engine rotation into electrical output.Spark Plugs
Spark plugs ignite the air-fuel mixture inside gasoline engine cylinders.
Create the spark needed for combustion at the correct time.Ignition Coils
Ignition coils turn low battery voltage into the high voltage needed to fire spark plugs.
Supply spark energy to one or more cylinders.Oxygen Sensors
Oxygen sensors monitor exhaust oxygen so the engine computer can adjust fuel mixture and catalyst checks.
Help control fuel trim and emissions monitoring.Catalytic Converter
The catalytic converter reduces harmful exhaust emissions using a coated internal catalyst.
Converts hydrocarbons, carbon monoxide, and nitrogen oxides into less harmful gases.Brake Pads and Rotors
Brake pads clamp against rotors to slow the vehicle through friction.
Turn vehicle motion into heat during braking.Cooling System
The cooling system moves heat from the engine to the radiator and cabin heater.
Maintains safe engine temperature with coolant, thermostat, radiator, fans, hoses, and pump.Fuel Pump
The fuel pump delivers fuel from the tank to the engine at the pressure required for combustion.
Supplies steady fuel pressure during starting, idle, and acceleration.Thermostat
The thermostat controls when coolant begins flowing through the radiator.
Helps the engine warm up quickly and then stay near its designed operating temperature.Radiator
The radiator releases engine heat from coolant into outside air.
Removes heat as coolant passes through thin tubes and fins at the front of the vehicle.Water Pump
The water pump circulates coolant through the engine, radiator, and heater core.
Keeps coolant moving so heat can leave the engine.Mass Airflow Sensor
The mass airflow sensor measures how much air enters the engine.
Helps the engine computer calculate fuel delivery.EVAP System
The EVAP system captures fuel vapors and routes them to the engine to be burned.
Prevents gasoline vapors from venting directly into the atmosphere.Purge Valve
The purge valve controls when stored fuel vapors enter the intake manifold.
Opens under computer control so fuel vapors can be burned at the right time.Wheel Bearings
Wheel bearings let the wheels rotate smoothly while supporting vehicle weight.
Carry wheel loads and keep the wheel hub rotating with minimal friction.CV Axles
CV axles transfer power to the wheels while allowing steering and suspension movement.
Deliver rotating torque through flexible constant-velocity joints.Struts and Shocks
Struts and shocks control body movement and help tires stay planted on the road.
Dampen suspension motion after bumps, braking, and cornering.ABS Wheel Speed Sensors
ABS wheel speed sensors report wheel rotation speed to the ABS and stability control systems.
Help the vehicle detect wheel lockup, traction loss, and stability events.Transmission Fluid
Transmission fluid lubricates, cools, and hydraulically controls many automatic transmissions.
Transfers hydraulic pressure, protects internal parts, and helps clutches and valves operate correctly.Torque Converter
The torque converter connects the engine to an automatic transmission using fluid coupling.
Lets the engine keep running while stopped and can lock at cruising speed for efficiency.Serpentine Belt
The serpentine belt drives accessories such as the alternator, power steering pump, water pump on some engines, and AC compressor.
Transfers engine rotation to accessory pulleys so charging, cooling, steering assist, and air conditioning can operate.Power Steering System
The power steering system reduces steering effort using hydraulic pressure or electric assist.
Helps the driver turn the wheels with less effort, especially at low speed and during parking.Brake Fluid
Brake fluid transfers pedal force through the hydraulic brake system.
Carries hydraulic pressure from the master cylinder to calipers, wheel cylinders, and ABS components.Engine Oil System
The engine oil system lubricates moving parts, helps carry heat away, and supports hydraulic components inside the engine.
Maintains oil pressure and film strength so bearings, camshafts, timing components, and lifters are protected.Engine Mounts
Engine mounts hold the engine and transmission in position while isolating vibration.
Limit drivetrain movement during idle, acceleration, braking, and gear changes.Vacuum Hoses
Vacuum hoses carry engine vacuum to sensors, valves, and control devices.
Route intake manifold vacuum for fuel trim, emissions controls, brake assist on some vehicles, and actuator operation.Fuel Injectors
Fuel injectors spray measured fuel into the engine for combustion.
Deliver the amount of fuel commanded by the engine computer to each cylinder or intake port.Throttle Body
The throttle body controls how much air enters the engine.
Opens and closes an air passage based on pedal input and idle control commands.EGR System
The EGR system routes a controlled amount of exhaust gas back into the intake to reduce combustion temperatures and emissions.
Helps control NOx emissions and can affect idle, pinging, and drivability when stuck or clogged.PCV Valve
The PCV valve controls crankcase vapor flow into the intake.
Ventilates blow-by gases so pressure does not build in the crankcase.Radiator Fan
The radiator fan pulls air through the radiator when vehicle speed is low or cooling demand is high.
Helps remove heat from coolant during idle, traffic, AC operation, and hot weather.Control Arms and Ball Joints
Control arms and ball joints locate the wheels while allowing suspension and steering movement.
Keep wheel alignment stable while the suspension moves through bumps, braking, and turns.