The coil pack is an essential component of a vehicle. Its main purpose is to transform the battery's voltage to the required amount of volts needed to fire the spark plugs. The coil pack consists of thin coils that are wrapped around a central core hundreds of times. Coil packs can become defective sometimes. When this happens, early signs usually appear, such as decreased engine power, rough idle or engine noise. Along with these symptoms, you can use certain techniques to determine if the coil pack in your vehicle is bad.
Open the hood of the vehicle and remove the electrical connector from the coil pack. This is located next to the engine oil dipstick in the engine compartment.2
Connect a spark tester or a 12-volt test light to the battery's positive terminal. Place the test light probe for the test light on each of the outside terminals of the coil pack connector.3
Stand at a safe distance from the vehicle and ask someone to start the car for you. As the car cranks up, check to see if the test light blinks. If the test light does not blink or there is no spark, that means that the coil pack is bad.