The battery supplies the power necessary to start the engine when the ignition switch is is turned on.

Combustion is the burning of an air-fuel mixture to provide energy. It requires the presence of air, fuel, and a heat source to ignite the air-fuel mixture. In the internal combustion engine that powers automobiles and trucks the combustion happens inside the engine utilzing a fuel like gasoline, diesel fuel, or natural gas.

The muffler follows the catalytic converter and absorbs sound to help quiet load exhaust. It is followed by the exhaust pipe which is the final exit point for exhaust gas from the vehicle.

The main computer or powertrain control module (PCM) uses pre-programmed software to analyze the input received from sensors and produce output signals to adjust vehicle performance and operation. (Engine control unit (ECU) is another name for the PCM.)

Spark plugs receive current from the distributor and use it to spark combustion in the combustion chamber of a cylinder.