How a Car Works from A to Z - a full explanation on exactly what occurs when you turn the ignition and put your foot on the gas


Jan 15th, 2019

How a Car Works from A to Z - a full explanation on exactly what occurs when you turn the ignition and put your foot on the gas

So how do the wheels of a vehicle turn? Exactly what happens to cause so much power? To the everyday person, he sits in the car and turns the key, and away he goes. But for those of us who feel the urge to find out exactly how and why this happens—here it is, explained in full—how a car works, from A to Z.

For a car to work, it takes more than just pushing the start button or turning the ignition key. A car is made up of many components, some big and some small. All these components work like a symphony, and the absence of an almost negligible component, like a fuse, may stop it from working.

To fully understand how a car works, we have to start with the parts that make up a car.

Three Major Classifications of Car Parts

The components of a car can be classified into three major groups, each part playing a vital role in making the car function. The absence of any of these components or their subsidiaries may stop the car from starting in the first place. Parts are classified under these three major groups:

1. Chemical Group

The chemical components of a car consist of all chemical substances that are employed to get a car started and keep it working. These components include the chemical compounds (aqueous acid) inside the battery of the car, the fuel (petrol or diesel) in the tank, and other chemical substances that the car uses. There’s no way a car can start without its chemical components.

2. Mechanical Group

This accounts for the major components of the car—from the materials that make up the engine block to the entirety of the wheels, axles, hubs, and brakes. The mechanical parts of a car are connected in such a way that one part makes other parts work. This means that if one mechanical component is faulty, the other parts might not function. 

The mechanical components of a car constitute more than 70% of the working parts in a car. If a car does not start or is not functioning well, the probability that the fault is mechanical is approximately 70%. The components that belong to this group are the engine, clutch system, transmission gearbox, steering system, and spark plug.

3. Electrical Group 

This group of components accounts for all the electrical fittings and wirings in the car. The electrical components in a car also incorporate the memory chips and the sound systems. Some of the most recognized electrical components are the starter motor, alternator, engine control unit, battery, and fuse.


The Engine

The engine is the core of any car. It is an intricate machine that works to transform the heat energy obtained during the combustion of gas into power, which then turns the wheels of a car. The series of processes which accomplishes this goal is kick-started by a spark, which ignites and rapidly burns the combustible materials inside the combustion chambers of an engine. The chamber is temporarily sealed during the combustion process. 

Internal combustion engine - the term “internal combustion engine” was coined from this chain of reactions inside the engine. The continuous combustion of the mixture of compressed air and petrol vapor leads to expansion, and in this way, power is generated to work the vehicle.

Main Parts of an Engine 

The workload on the engine of a car is massive, and so the engine must have a strong structure that can withstand the pressure acting on it. An engine has two fundamental parts: 

  • Cylinder block - this section is heavy and is the underlying area of the engine. It houses the major moving components of the engine.

The cylinders in an engine block are moulded into the block, in the same way that other auxiliary hardware mountings for auxiliary hardware are moulded. As an example, in the oil filter that provides a passageway for the oil that greases the engine and the fuel pump, an oil reservoir or sump is attached to the base of the crankcase. An engine block is usually made of cast iron.

  • Detachable lid - it serves as the head of the cylinder. The detachable cylinder head encapsulates a series of valve-controlled paths that provide passage for the combustible mixture designated for the cylinders. It also offers passageways for the expelled gases after combustion. The head is often made in the same metal as the block, but aluminum is often preferred since it is light and efficient in dispelling heat.
  • Crankshaft - the crankshaft is housed by the engine block, and it transforms the repetitive movements of the pistons into circular motions at the crankshaft. Sometimes, the engine block also contains the camshaft, which works components that engage and disengage the valves housed in the cylinder head. In some cases, the camshaft is contained in the cylinder head joined with the pistons.
  • Flywheel - another major component of the engine is the flywheel. It is a metallic disc that is connected to the end of the crankshaft of the engine. During ignition, this disc is worked by the pinion of the starter. It also helps in smoothing out pulses created by each piston in the engine block for effective transmission of power.

Engine Designs 

There are three distinctive engine designs, namely:

  • In-line engine 

The least complex and most common kind of engine is made up of four vertical barrels or cylinders laid near one another in succession. This kind of engine is referred to as an in-line engine. If the capacity of a car surpasses 2,000 cc, its engine probably contains six cylinders.

  • V-8 engine

In some autos (usually the more compact kind), you will find the V-engines fitted in them, particularly in cars that have 8/12 cylinders, and a few others that only have 6 cylinders. In these cars, the cylinders are lined up in such a way that they are perpendicular to each other.

  • Horizontal-opposed engine

In certain engines, the angle at which the cylinders are arranged is extended to 180 degrees. This type of engine is known as horizontally-opposed engine, which is an augmentation of the V-engine. It is a good choice if you want to take advantage of its height-saving and equalizing properties.

The Clutch System

The work of a clutch in a car is simple – it tells the transmission to either engage or disengage power. The clutch of a car is linked with drive shafts, where one is the drive member and the other is the driven member. The driving member is connected to the engine of a car, and the driven member is responsible for providing output power.

The Transmission/Gearbox

A car’s transmission system may be any of these types—manual, automatic, or continuously variable transmission (CVT). CVT transmissions are not so common but have been in use for quite some time. Regardless of which one is used by a car, the function of a transmission system is the same—to facilitate gear change.

The transmission in a car is what you engage when you put a car in drive or reverse. In automatic and CVT transmission cars, the transmission varies the change of gear on its own. Without the transmission, the car will not leave the spot on which it stands.

The Steering System

The steering system contains everything that connects the steering wheel of a car to its wheels. The steering wheel is linked directly with the steering gearbox which is linked to the track rod by a pitman arm. The track rod is then linked to the wheel of the car with a tie rod. In most cases, there is an idler arm, which is also connected to the track rod.

When the steering wheel of a car is turned, it results to the same rotation in the wheels. However, a long turn of the steering wheel may result in a small turn in the wheels of the car.

The Spark Plug

The spark plug of a car is a small component of the engine that sparks up the combustible fuel in the combustion chamber. This is done by conveying the electric current from the battery or alternator to the combustion site. Although diesel engines don’t require the spark from a plug to function, it serves a critical purpose in the spark-ignition engine like the four-stroke petrol engine.


The Starter Motor or Kick Starter

The starter motor of a car, often called kick starter, is primarily in charge of all the processes associated with starting up a car. The starter works by taking electrical power from the battery. When the car key is inserted and turned, or when the start button is pushed, a small amount of current courses into the starter relay. 

Components of a Kick Starter 

The kick starter is made up of several components that work together to achieve the one goal—to get the car started. These components are:

  • Pinion – it is located at the head of the starter and directly linked to the field wiring and commutator. It is used for turning the flywheel of the engine during ignition.
  • Solenoid – it disengages the pinion of the starter when the flywheel is spinning so that the teeth of the pinion will not be damaged.
  • Return spring – it is directly connected to the solenoid and is linked to the pinion through the actuating arm. When the flywheel spins, the solenoid pulls back the return spring, while the return spring pulls the actuating arm to turn off the starter.
  • Actuating arm – it connects the solenoid to the pinion so that when the need comes for the solenoid to disengage the pinion, it does so by using the actuating arm. 
  • Field winding - this is a group of wires (mostly copper) that rotates between two opposite magnets to generate motion when an electric current is supplied to the starter.
  • Commutator and brushes - when the field winding moves in the magnetic field, the commutator and brushes stop it from having a torque reversal.

Location of the Starter 

The starter can be found generally in the front of the engine of a car. Sometimes, however, the starter is placed at the back of the engine. When the power from the battery is not sufficient, the starter will not be able to harness enough power to start up the engine of the car. 

The Alternator

The alternator supplies majority of the electrical necessities of a car. An alternator is just like a phone charger – it is responsible for charging the battery of the car. It is made up of copper coil with bipolar magnets in-between to generate current each time the shaft of the alternator turns. The electrical load of a car falls on the alternator when the car is operational. 

When the load exceeds the capacity of the alternator, the battery will have to come to its aid. The alternator is connected to the engine with the means of a pulley belt, and the tightness of this belt can affect the total output of the alternator.

The Brainbox or the Engine Control Unit (ECU)

Cars have a brain for controlling its complex operation. The ECU or PCM (Powertrain Control Module) or brainbox of a car is a multilayer circuit board made up of electronics. It accepts and processes the various pieces of information that come from diverse sensors in the car’s engine and other parts of the car. It is a very powerful part since it controls most of a car's functions. For instance, it controls the central locking system in your car.

During ignition, the ECU translates information to the involved areas—where electrical current is needed, when to inject fuel, and when to expel emissions from the car. 

The Battery

The battery of a car is responsible for storing electrical charge so that it can be called upon to deliver the stored electricity when the alternator is not active. It supplies electrical current to the starter during ignition. When the car is running, it can supplant the alternator when the need arises. 

Batteries provide the power that is required to get cars up and running. They have no tolerance for deep discharge, and their life span can be reduced by 70 percent or more if the charge in them is completely depleted. When a battery is fully charged, it can supply up to 12.6 volts.

The Fuse

Fuses safeguard the electrical wiring and the electrical components in a car. Sometimes the electrical current from the alternator can surge higher than normal, which may lead to the damage of the electrical equipment in the car. The fuses are used in closing the electrical circuits in a car so that when a direct current surpasses their capacity voltage, they’ll break without causing any harm to the electrical equipment.

Types of Automotive Fuses 

There are four major types of automotive fuses, and these are:

  • Blade type – this is a very common type. It is built in plastic, with two metallic legs for connecting to sockets. Blade-type fuses come in six different sizes—micro2, micro3, LP-mini, mini (APT or ATM), standard or regular, maxi (APX). Blade type fuses adopt a color code scheme to represent current rating. For instance, dark blue for 0.5A, black for 1A, gray for 2A, and so on. The highest current rating for this type of fuse is purple (120A), which is maxi in size.
  • Bosch type - this type of fuse is mostly used in old European cars. It measures 6mm x 25mm with pointed ends. Bosch types also use color to indicate their current rating, that is, yellow for 5A, white for 8A, red for 16A, blue for 25A, and gray for 40A.
  • Lucas type - this type is mostly used in British-assembled cars. Its sizes fall between 25mm and 32mm with pointed ends. Lucas type fuses also use color to represent a current rating, but which varies based on three criteria—continuous ampere (equal to the rated current), instantaneous ampere, and continuous fusing ampere. For instance, a blue color fuse can have a value of 1.5A for continuous ampere, 3.5A for instantaneous ampere, and 3A for continuous fusing ampere.
  • Glass-tube type - the current rating for this type of fuse depends on its length. This fuse was introduced by the Society of Fuse Engineers (SFE). This type of fuse is designed in such a way that a thread-like resistance wire is linked to metal at both ends and encased in a glass tube.
  • Limiter type - this type of fuse is mostly used in electric cars.

How Does a Car Work?

At this point, you already know the major components of a car and their purpose in its operation. Now that we’ve gotten that out of the way, we may now go into the details of how a car works.

The operation of a car may seem like a simple process from the surface, but as you turn the ignition key of the car, a sequence of events takes place. We’ll discuss what these events are and how the mechanical parts of the car communicate with each other to ensure a smooth ride.

The Ignition Process 

Step 1 – The ignition key is inserted into the switch. 

As soon as you insert your car key into the ignition switch, you have completed the first step in getting your car started.

Older car models (from one or two decades ago) may not have security chips embedded in their ignition key, but the newer models do. When you put your key in the ignition key, the brain box will immediately run a security check on your key. Should you use a key that is cut to look like your car key, it may not start your new model car because it won't pass the key security check.

For newer models that use keyless entry systems and a push button start, the same security check takes place. However, unlike the ignition key systems, the keyless entry cars use wireless sensors to conduct their security check on the key. When you use the right key, the sensor picks up the signal from the key and the car starts even before you push the START button.

Once your key passes the security check and you turn the key in the ignition switch or press the start button, you move to the next step in the ignition process.

Step 2 – The starter is fed with electrical current.

A brief reminder: the starter is primarily in charge of all the process associated with starting up a car.

When you turn the key in the ignition switch, the brain box communicates this command to the starter by supplying electrical current stored in the battery to the starter.

The starter is electrically operated, that is, the electric current from the battery enters its components—the magnetic field windings, the commutators, and the solenoid which controls the magnetic circuit to prevent the starter from getting damaged.

The starter requires strong electrical current from the battery, and for that reason, it is connected to the battery using thick high-resistance wires. In the absence of strong electric current (such as the case when the battery is weak or without sufficient charge), the starter will not engage the engine of the car.

If the starter is fed with strong electrical current when you turn the ignition key, the starter spins its pinion (which is attached to the flywheel) rapidly.

The process of turning the flywheel happens very fast, after which the starter disengages from the flywheel, and its work is done.

Step 3 – Fuel is pumped into the engine.

The spinning flywheel activates the fuel pump of the car. The unfiltered fuel passes through the fuel filter inside the fuel tank.

The filtered fuel is then supplied through the valve-controlled pathways in the cylinder head to the combustion chamber in the engine block cylinders. Some cars have injectors mounted on their engine block cylinder head, and this injector controls the inflow of fuel to the combustion site. The injector also dictates the amount of fuel that goes into the engine to prevent overflow of fuel in the cylinders.

The fuel pumped into the combustion chamber of the engine block is vaporized. This vaporized petrol is also mixed with air (a combustible mixture of petrol and air).

Step 4 – Combustion takes place in the engine.

During combustion, the combustible mixture inside the cylinder is burned to produce the power that turns the wheels of the car. Generally, the combustion process follows this sequence: 

  • Intake - the process starts with the intake of vaporized fuel and air. When this mixture enters the cylinder, the pistons are raised to let it in.
  • Compression - the raised pistons fall on the combustible mixture, compressing it.
  • Explosion and expansion – the electric current, in the form of spark, ignites the combustible mixture and triggers an explosion. This explosion of the compressed mixture inside the combustion chamber of the engine block leads to an expansion of the hot air in the cylinder. This expansion leads to the lifting up of the pistons that compressed the mixture in the first place.
  • Exhaust – the explosion produces smoke, which is taken from the cylinders, let out through the outlet valve, and expelled through the exhaust pipe. 

Note: The entire process of combustion happens very fast, and the continuous repetition of the process turns the camshaft in a rotatory motion.

Step 5 – The engine transmits power to the alternator.

Crankshaft and camshaft - the continuous combustion of fuel in the cylinders brings about the rotation of the engine (crankshaft and camshaft). The crankshaft and the camshaft both have metallic discs or pulley attached to their right end, and these discs drive a belt known as the engine belt. 

Engine belt - this engine belt is connected to other components—the water pump, power steering pump, and AC compressor. It is linked with the pulley on the alternator so that the rotation in the engine will power it. When the pulley on the alternator rotates, the alternator produces power through electromagnetism.

How It Works 


An alternator comprises of two parts—the rotor and the stator. 

  • Rotor – the movable part of an alternator. It is linked directly to the alternator pulley, and fitted in such a way that it comes very close in contact with the stator, without touching it. 
  • Stator – the fixed part of an alternator. It is designed in such a way that three sets of wires are looped and are uniformly distributed to create a 3-phase system.

The rotor in the alternator is an electromagnet, so when it turns inside the hollow of the 3-phase system of the stator, electric current is generated.

Voltage regulator

A voltage regulator is connected to the alternator to control the outputted voltage. This connection can be done in two ways—either the voltage regulator is mounted externally on the alternator casing or built-in within the case.

The voltage produced by the alternator is usually between the range of 13.5 volts and 14.5 volts. Depending on the current requirements of the car, the voltage regulator can engage or shut down the charging process of the alternator. The voltage regulator accomplishes this objective by varying the applied field current of the rotor.

Voltage less than 13.5V – if the voltage goes below the 13.5-volt mark, the voltage regulator will take it upon itself to step in to begin the charging process by applying current to the field. 

Voltage more than 14.5V – the reverse is true if the voltage surpasses 14.5V. When this happens, the voltage regulator will halt the alternator's charging process by removing the applied current from the field. 

If you have a faulty voltage regulator, it will not be able to do its job properly. The voltage in the alternator could exceed its maximum level and cause damage to the car. The presence of a fuse reduces the damage in this situation, and the worst you get is a burnt fuse. 

Once the engine is up and running, the alternator supplies electricity to every part of the car that needs it. This step concludes the ignition process. 

Moving the Car

Getting the car started is one thing, moving it requires another series of process. Whether you plan to move it forward or you choose to put the car in reverse motion, certain things have to happen before the car moves.

The process of moving a car is similar in both automatic transmission and manual transmission cars. However, the process of getting a manual car to change its position from one spot to another is much more complex than the automatic process.

Step 1 - Start by putting your foot on the brake pedal.

In manual transmission cars, when you put your foot on the brake pedal, the result is that your car will be halted or will not move on its own. However, in automatic transmission cars, putting your foot on the brake pedal does more than that. It sends a signal to the powertrain control module (PCM)—or the brainbox—that you are ready to engage the gear.

The brain box communicates this message to the sensors in the gearbox, and the gear stick frees up. In manual transmission cars, the clutch serves this purpose. However, in an automatic transmission, the clutch is often embedded in the transmission or coupled with the gearbox.

When you decide to move an automatic transmission, it is necessary to put your foot on the brake pedal otherwise you wouldn’t be able to engage a gear.

Step 2 – Step on the clutch (for manual transmission only).

The clutch pedal in manual transmission cars disengages the gear and puts the car in a temporary neutral position. You cannot engage the gear in manual transmission cars without using the clutch because it controls the valve in the transmission box that opens up the gear pathways when you want to engage a gear.

Step 3 – Engage the gear.

You need to put the car in gear before you can accelerate. This is true for all three types of transmission system. 

Engaging the gear in automatic transmission cars – when you put your car in DRIVE, this is what happens: 

The torque converter pump in the automatic transmission case gets power from the engine and uses this power to pump transmission fluid to the turbine. This turbine is linked with a driving shaft that is also connected to a wheel (in front wheel cars), and so the turbine turns the shaft, and the car begins to move. As you step on the accelerator, this process is repeated rapidly, and the turbine speeds up to move the car faster. As you accelerate, the gear ratio is varied by means of sensor-controlled valves in the transmission.

Engaging the gear in manual transmission cars – the gear arrangement is mapped out in such a way that when you shift the gear stick, the gear falls into a number (usually from 1 to 5, but some newer models have their gear numbered to 6 or 7). Here’s how the process goes:

When you press your clutch pedal and engage gear, for instance, you put the gear in the 1 position the engine activates the torque converter pump. The turbine turns the shaft, and the car moves. You will have to vary the clutch with the accelerator to get your car moving. As you reduce pressure on the clutch pedal, you simultaneously increase pressure on the accelerator pedal. When you want to increase speed in the manual transmission cars, you have to vary the ratio of your gear by yourself. For instance, when you want to change from gear 1 to gear 2, you must repeat the whole gear procedure. 

When you put the car in reverse gear, the same thing happens. But, instead of a forward spin of the driving shaft by the torque converter turbine the driving shaft spins in reverse.

Step 4 – Use the steering wheel to turn the wheels.

The moment a car starts to move, a new need arises—keeping it on the desired path. You use the steering wheel for this purpose. It turns the wheels of the car to the right or left direction.

A quick reminder: The steering wheel is linked directly with the steering gearbox which is linked to the track rod by a pitman arm. The track rod is then linked with the wheel of the car with a tie rod.

Usually, the steering is preset to maintain a balanced angle that will keep the car moving on a straight path until the steering is turned towards another direction.

The wheel of a car is connected to the tie rod with the aid of hubs, axles, and brake discs or drums. These components make the wheel turn without breaking the tie rod.

Stopping the Car

The wheels are attached to discs that have brake pads for reducing speed or halting the car.

Automatic - in automatic transmission cars, putting your foot on the brake pedal tells the braking system to put pressure on the brake discs. This information is communicated by means of the brake fluid.

Manual - in manual transmission cars, you need to disable your transmission by putting your foot on the clutch before you start applying the brakes.

This concludes our article on how a car works. A lot of time and effort went into the completion of this masterpiece. I hope it has given you an idea about how the main auto parts of a vehicle work together to make it move and stop. Its goal is to help everyone—from young future mechanics who want to get into the trade and right up to the DIY home mechanics who have that inner longing to learn. 

If you have any question or have a topic in mind you would like me to write about, please feel free to email me at