Ignition coil — what is it and how to check it?

The ignition system requires electricity to function. Without electricity, the engine will not be able to convert the fuel mixture into the energy necessary to move the vehicle. The ignition coil is responsible for transmitting it. How is it constructed, what are the symptoms of its damage and how to check the ignition coil? We give you a hint!

Several elements are responsible for accumulating and transmitting electricity, but the coil plays a key role among them!

Ignition coil — structure and operation

The main task of the ignition coil is to accumulate electrical energy taken from the battery. It changes low voltage current into one that reaches up to 30,000 volts. Thanks to such a high voltage, the system can produce a spark that starts the combustion process.

What does an ignition coil consist of?

The construction of this part is quite simple. It consists of two coils of wires, i.e. the so-called primary and secondary turns. Primary ones are thicker but smaller and have a positive charge. They are used to collect electricity. The secondary coil, however, has a negative charge, which is not as thick, but is made of up to 100 times thinner wire. The coils are built with a tight core of metal plates, covered with special and tight insulation. The entire mechanism is enclosed in a plastic housing.

How does such a coil work?

The current reaches the winding, where it is accumulated and turned into a magnetic field. The field then breaks down and an induction current is created (by closing the circuit). Later it passes to the secondary coil, which increases its tension. A sudden and controlled interruption of the circuit releases a huge current, which goes to the spark plug through a high-voltage contact , which turns it into a spark.

Symptoms of ignition coil damage — how to detect them?

The most common symptoms of damage include fluctuating engine speeds, jerking when accelerating (or at idle), much higher fuel consumption or problems with starting.

There are cases where the driver has problems with starting the vehicle during high air humidity (rain, snow, morning). A damaged coil then does not transmit the spark to the spark plug, but releases it outside the system (moisture is then a natural conductor).

Symptoms of a damaged coil also include a check engine light on the dashboard, lack of proper functioning of all cylinders and problems with driving on a cold engine. As you can see, there can be many of them. Therefore, you need to diagnose the fault directly on the coil.

How to check the ignition coil?

To diagnose whether an electrical component in your car is working, you need to use an ohmmeter. This is equipment that allows you to see what current values ​​the coil absorbs and processes . How to check the ignition coil using it?

First, connect an ohmmeter to the coil and check the resistance. Correct values ​​may vary significantly depending on your car and engine type. Before taking measurements, check what guidelines are provided in the manual of the car or the coil itself. If the values ​​do not meet the guidelines, the coil will need to be replaced.

Unfortunately, it is not always possible to check the ignition coil with a simple ohmmeter. If there is an internal short circuit between the turns, the only diagnostic device will be an oscilloscope available in workshops. Sometimes mechanics also use computers that will directly indicate coil damage.

When is it necessary to replace the ignition coil?

The ignition coil is not a device that you need to replace as a spare. You should only install a new element if the old one is damaged. Sometimes a high-quality coil can last up to 200,000 kilometers.

However, replacing the ignition coil is necessary when it fails, which is why it is so important to check it. It’s not just about internal faults affecting the engine’s operation. For example, the casing may be damaged. Then you absolutely need to install a new device. The huge current from the coil can pass through, for example, the car body and electrocute you. There are also known cases of spontaneous combustion.