Car Parts Explained

What each part actually does, how it works, the symptoms when it fails, and the trouble codes it sets — in plain language. New components are added regularly.

• Alternator

  The alternator is the vehicle's power plant: spun by the engine's belt, it generates the electricity that runs everything and recharges the battery.

• Catalytic Converter

  The catalytic converter is a chemical reactor in your exhaust that converts the engine's three worst pollutants into carbon dioxide, water, and nitrogen, using precious-metal coatings at high temperature.

• EGR Valve (Exhaust Gas Recirculation)

  The EGR valve routes a measured dose of exhaust gas back into the intake.

• Fuel Injector

  A fuel injector is an electrically-controlled valve that sprays a precisely measured mist of fuel for combustion — opening and closing in milliseconds, thousands of times per minute.

• Ignition Coil

  An ignition coil is a compact transformer that turns the battery's 12 volts into the 25,000–45,000 volts a spark plug needs to ignite the mixture.

• Mass Air Flow (MAF) Sensor

  The MAF sensor measures exactly how much air enters the engine — the single number all fuel delivery is calculated from.

• Oxygen Sensor (O2 Sensor)

  An oxygen sensor measures how much oxygen remains in the exhaust and reports it to the engine computer many times per second, letting it fine-tune the fuel mixture in real time.

• Thermostat (Engine Cooling)

  The thermostat is a temperature-operated valve that blocks coolant flow to the radiator until the engine warms up, then continuously regulates flow to hold operating temperature.