# Ignition coil

> The ignition coil is a transformer that steps up the low voltage from the CDI or ECU to the many thousands of volts needed to fire the spark plug.

- **Also known as:** Bobin, Buji bobini, HT coil
- **Turkish term:** Ateşleme bobini
- **Category:** [CDI Units & Ignition Coils](https://motorsikletparcasi.com/en/category/cdi-units-and-ignition-coils)
- **Page:** https://motorsikletparcasi.com/en/glossary/ignition-coil

When the current in the coil's primary winding is cut suddenly, a very high voltage is induced in the secondary winding and carried to the [spark plug](https://motorsikletparcasi.com/en/glossary/spark-plug) through the HT lead and plug cap. Modern engines may use a "stick coil" that sits directly on the spark plug.

## Symptoms of a problem

- A weak or yellow spark
- Misfiring in the rain or after washing (cracked body, damp cap)
- Cutting out at high revs

Plug caps and HT leads harden and crack with age, so check them together with the coil.

## Related terms

- [CDI (capacitor discharge ignition)](https://motorsikletparcasi.com/en/glossary/cdi): A CDI (capacitor discharge ignition) unit stores energy in a capacitor and dumps it into the ignition coil to create the spark at the spark plug.
- [Spark plug](https://motorsikletparcasi.com/en/glossary/spark-plug): A spark plug ignites the fuel-air mixture in the cylinder with a spark across its electrodes.

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- Source page: https://motorsikletparcasi.com/en/glossary/ignition-coil
- Last updated: 2026-10-09
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