2004 Audi A4 Ignition Coil

What does an ignition coil do?

An ignition coil is one of the most important parts of the ignition system and has a lot of responsibility. The role of the ignition coil is to transform the 12 volts of battery power into high voltage to produce a spark in the spark plug. This generated spark then kindles the mixture of fuel and air in the engine cylinder, and the car is able to run and take you places.  
In the modern day, cars have a single coil for each cylinder. The ignition coil is usually fitted right above the spark plug. This position of the ignition coil is called a coil-on-plug setup. As the ignition coil is a major part of the engine, it should be taken care of. If the ignition coil fails at some point, your engine will not perform at all. Damaged and faulty ignition coils can be a reason for a significant safety threat. Furthermore, if you don't take care of the ignition coil, it could lead to costly repairs.

How to tell if an ignition coil is bad?

A faulty ignition coil can cause a variety of problems in your vehicle. Check these signs and symptoms of a bad ignition coil to help you determine if it needs replacement:

• Engine misfires: Uneven engine operation or stumbling.
• Difficulty starting: Prolonged cranking before the engine starts.
• Reduced power: Decreased engine performance and acceleration.
• Stalling: The engine may stall, especially when idle.
• Check engine light: Illuminated dashboard warning.
• Rough idling: Unsteady engine idling.
• Increased emissions: May fail emissions tests.
• Spark plug issues: Wet, sooty, or unusual wear on spark plugs.
• Unusual engine sounds: Popping or sputtering from the exhaust.