How It Works

Ignition coils are a key component of a car's ignition system. They take the low voltage from the battery (12 volts) and transform it into a much higher voltage (typically up to 45,000 volts) that is required to create a spark at the spark plug. This spark ignites the fuel and air mixture in the engine's cylinders, providing the power to move the vehicle.


Ignition coils work on the principle of electromagnetic induction. They consist of two coils of wire wrapped around a core, typically made of iron. The primary coil, which has fewer turns of wire than the secondary coil, is connected to the car's battery and the electronic control unit (ECU). The secondary coil, which has more turns of wire, is connected to the spark plug.


When the battery voltage is applied to the primary coil, it creates a magnetic field around the coil. When the ECU signals to interrupt the flow of current to the primary coil, the magnetic field collapses, inducing a high voltage in the secondary coil. This high voltage is then sent to the spark plug, which creates a spark that ignites the fuel and air mixture.


If the ignition coil fails, the spark plug will not receive enough voltage to create a spark, resulting in a misfire, poor performance, or even a complete failure to start. Ignition coils can fail due to heat, vibration, and wear over time. Signs of a failing ignition coil include engine misfires, backfires, poor performance, and a reluctance to start.


Types Of Ignition Coils

There are several types of ignition coils, each with it’s own unique design and function.

The ignition coil typically comes in 6 variants:

  1. Distributor ignition coils
  2. Block ignition coils
  3. Pencil coil with dual spark technology
  4. Block ignition coils with two high-voltage outlets
  5. Pencil coil with single spark technology
  6. Ignition coil systems


Distributor Ignition Coils: These are the traditional ignition coils that were used in older vehicles. They are usually mounted on the engine block and are connected to the distributor through high-tension wires. When the distributor sends a signal to the coil, it generates a high voltage that is sent to the spark plugs.


Block Ignition Coils: These coils are typically mounted on the engine block and generate high voltage that is distributed to the spark plugs through high-tension wires. They are usually single-output coils, meaning that each coil is responsible for firing a single spark plug.


Pencil Coil with Dual Spark Technology: These coils generate two sparks per ignition cycle, which can help to improve fuel efficiency and reduce emissions. They are typically mounted directly over the spark plug and are controlled by the engine's electronic control unit (ECU).


Block Ignition Coils with Two High-Voltage Outlets: These coils are similar to block ignition coils but have two high-voltage outlets, which allows them to fire two spark plugs simultaneously.


Pencil Coil with Single Spark Technology: These coils are similar to the pencil coils with dual spark technology, but they only generate a single spark per ignition cycle.


Ignition Coil Systems: These are more complex ignition systems that use multiple coils to generate high voltage that is distributed to the spark plugs. They are typically found in high-performance or racing vehicles, where they can provide more precise control over the ignition timing and improve engine performance.



Why Do Ignition Coils Fail

The reasons for ignition coil failure can vary depending on the specific type of coil, as well as other factors such as usage, maintenance, and environmental conditions. For example, distributor ignition coils may be more prone to failure due to wear and tear on the distributor cap and rotor, while pencil coils may be more prone to failure due to overheating or internal wiring issues. However, common causes of ignition coil failure across all types can include excessive heat, moisture, vibration, and electrical overload:

Overheating: Ignition coils generate a lot of heat during operation, and if they get too hot, the insulation around the coil windings can break down, leading to a short circuit or open circuit.

Age and wear: Over time, the coil windings can become worn or damaged, leading to a decrease in the coil's ability to produce voltage. In general, most ignition coils are designed to last for at least 150,000 kilometers or more, but some may fail earlier or last longer.

Contamination: Dirt, oil, or other contaminants can get into the ignition coil and cause it to malfunction.

Voltage overload: If the ignition system's voltage is too high, it can cause the coil to overheat and fail.

Vibration: Vibrations from the engine or other sources can cause the coil's internal connections to become loose, leading to a loss of electrical contact.


Signs and Symptoms Of A Failing Ignition Coil:

There are several signs that can indicate a failing ignition coil, including:

Engine misfires: If the ignition coil is not working properly, it may not be able to provide the spark needed to ignite the fuel in one or more cylinders. This can cause the engine to misfire, which will result in a noticeable lack of power and a rough running engine.


Check engine light: A failing ignition coil can trigger the check engine light on the dashboard. The engine control module (ECM) will detect a problem with the ignition system and store a diagnostic trouble code (DTC) in its memory.

Poor fuel economy: If the ignition coil is not working properly, it may cause the engine to run inefficiently. This can lead to a decrease in fuel economy, as the engine will have to work harder to compensate for the lack of power. 

Hard starting: A failing ignition coil may cause the engine to be hard to start, as there may not be enough spark to ignite the fuel in the cylinders.

Rough idle: If the ignition coil is not working properly, it may cause the engine to idle rough or stall.

If you are experiencing any of these symptoms, it is important to have your vehicle diagnosed by a qualified mechanic to determine if a failing ignition coil is the cause.

How We Can Help

If you suspect that your ignition coils need replacing, the first step is to take your vehicle to a qualified mechanic or automotive technician for a proper diagnosis. Your mechanic will visually inspect the coil casing for signs of physical damage, such as cracks in the coil casing or spark plug boot.  After that, there are a number of ways to test the ignition coils, such as a Spark test or Power Balance Test.

If you need to replace your ignition coils, be sure to visit They stock a comprehensive range of replacement pencil coils and coil packs, which cover the majority of the South African carpark. Simply input your make, model and year and the correct ignition components will appear.

As always, if you need any help, feel free reach out to our technical team