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Ignition Coil

In this article, you will learn about ignition coils, how they work and symptoms you may notice when they fail. 

What is an ignition coil?

ignition coil problem replacement cost

An ignition coil is an induction coil in an automobile's ignition system that transforms 12 volts to the thousands of volts needed to create an electric spark at the spark plugs.

A coil pack is a collection of ignition coils that eliminates the expensive and troublesome distributor, cap, and spark plug wires.

Coil packs provide better engine performance than distributors used in older vehicles. Some early coil packs were prone to frequent failure. But the modern ones can potentially deliver a better spark with less produced electrical noise. It is also worth mentioning that coil packs have a much longer lifetime than distributors.

How does an ignition coil work? 

check engine light on ignition coil light

When the combustion process starts, the coil pack or ignition coil produces very high energy that reaches 75,000 Volts.

The ignition control receives a signal from the car's computer which releases the voltage from the coil pack that goes through the spark plug.

When the current travels to the spark plug, the spark plug fires an explosion inside the cylinder chamber due to the fuel-air mixture.


  • Experiencing repeated misfiring and backfiring
    • A faulty ignition coil, unburned gasoline smell might be emitted through your exhaust, which can also cause costly and unnecessary repairs.
    • Black exhaust smoke could be emitted due to different reasons, but a bad ignition coil is always a probability.
    • Engine runs poorly or has excessive vibrations.
  • Problem starting up the engine
    • The vehicle takes a long time to start or doesn't start at all, especially in cold weather because the ignition will not be able to transmit the needed amount of charge to each spark plug.
  • Check engine light comes on 
    • The ECU has a log for faults, in which it records the sensor's readings and reports them to the driver through the check engine light in the dashboard.
  • Vehicle stalls
    • If your ignition coil is failing, your coil will emit irregular sparks to the plugs to keep it running. When you stop your car, it may splutter or shut off completely.
  • A noticeable lack of power
    • Engine RPMs drop suddenly and repeatedly when trying to accelerate, vibrations at idle speed, and unstable overall driving experience.
  • Lower fuel economy
    • If the spark plugs are not receiving the required amount of electric spark, this would cause the engine to struggle for power, which would dramatically affect the car's overall fuel consumption.
  • Spark plugs
    • When spark plugs start wearing out or become faulty, resistance builds up which causes more heat, and that is the worst thing you could do to your ignition coil.
    • Driving under any of these conditions can damage the catalytic converter over time, which will increase the cost of the repair.

How to find out if you have a bad ignition coil

symptoms of bad ignition coil

Once an ignition coil fails it will trigger the check engine light and the engine may start to shake. To find out if you have a bad ignition coil, you can start by reading the fault codes. 

To do this you will need an OBD2 scanner.

  1. Plug the code reader under the 16 pin port located under the dashboard on the driver's side.
  2. Turn the key to the ON position.
  3. Hit read on the scanner.
  4. Wait a couple of minutes.
  5. You will have a diagnostic trouble code (DTC) displayed on the screen.

Codes that are related to bad ignition coil are:

  • P0354 Ignition Coil D Primary/Secondary Circuit

  • P0351 OBD-II Trouble Code: Ignition Coil "A" Primary/Secondary

  • P0352 OBD-II Trouble Code: Ignition Coil B Primary/Secondary Circuit

  • P2311 OBD-II Trouble Code: Ignition Coil D Secondary Circuit

You may also notice P0300, P0301, P0302, P0303, P0304, P0305, P0306 cylinder misfire codes yet.

Don't worry about these codes. Replace the defective ignition coil, erase all codes with the OBD2 code reader and see if these codes come back.

The following video shows how to find a faulty ignition coil with any tools. 

You can verify the ignition coil is bad, by swapping the existing coils. If the code moves with ignition coil you have confirmed the ignition coil is faulty. 

What do ignition coils fail?

spark plug igntion coil problem

The main reason for ignition coils failure is worn spark plugs, excessive spark plug gap, or plugs wires.

Heat can also affect the windings and insulation of the coil. The ignition coil increases the primary voltage from 12 Volts up to 40 thousands of Volts to fire the spark plugs. If there's an open plug wire or excessive resistance, the output voltage can burn the internal insulation of the coil.

Another reason for ignition coil failure is oil or coolant leaks which might damage the ignition coils.

Types of Coil Ignitions

  1. Coil-On-Plug (COP) is the most preferred system setup for various performance, maintenance, emission, and packaging reasons. This system reduces the resistance between the coil and the plug, and also reduces interference of radio frequency, which consequently eliminates potential misfire problems. It also eliminates the need for complex, expensive and long high-voltage spark plug cables.
  2. Coil-Per-Cylinder (CPC) systems improve the engine?s ability to reduce oxides of nitrogen emissions, which is essential for today's cars emission standards. It gives each coil more time to recharge between cylinder firings, which mean a hotter spark that result in fewer misfires, backfires, better fuel consumption and cleaner combustion.
  3. Coil-Near-Plug (CNP) systems were fitted in late V8 models, this setup is used because the plugs stick from the cylinder head side and there is no much room to fit a coil on the end of the plugs.