vehicles ignition coil

Ignition Coil

What is an Ignition Coil, what does it do, and how does it works? Read the procedures below to learn how is an Ignition coil and how it works on our vehicle.

What is an ignition coil?

An ignition coil is an induction coil in an automobile’s ignition system that transforms 12 volts into 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 electrical noise. It is also worth mentioning that coil packs have a much longer lifetime than distributors.

How does an ignition coil work?

ignition coil problems

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 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, or an unburned gasoline smell might be emitted through your exhaust, which can also cause costly and unnecessary repairs.
    • Black exhaust smoke could be emitted for different reasons, but a bad ignition coil is always probable.
    • The 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 fault log, which 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 do not receive the required amount of electric spark, this would cause the engine to struggle for power, dramatically affecting 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, increasing the repair cost.

How to find out if you have a bad ignition coil

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. A simple OBD-II Scanner can read and clear fault codes on a vehicle’s Engine Control Unit.


If you want a more professional OBD-II Scanner, use the YOUCANIC Full System Scanner to read and clear fault codes through every vehicle’s control module.

  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. A diagnostic trouble code (DTC) will be 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, and 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.

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

What do ignition coils fail?

spark plug gap

The main reason for ignition coil failure is worn spark plugs, excessive spark plug gaps, or plug wires.  Heat can also affect the windings and insulation of the coil. The ignition coil increases the primary voltage from 12 to 40 thousand 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 radio frequency interference, which 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 car emission standards. It gives each coil more time to recharge between cylinder firings, which means a hotter spark that results 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 not much room to fit a coil on the end of the plugs.

We hope you find the Ignition Coil guide helpful. Check these troubleshooting and repair guides for more help on your vehicle.


  • Rushit Hila • ASE Certified

    Rushit Hila, an ASE-certified engineer (G1 Automotive Maintenance and Repair), brings over two decades of hands-on experience in the automotive world to his writing. With a strong educational background, including a Master of Science in Engineering and a Bachelor of Science in Engineering, he has honed his skills and expertise through years of practical work. As a respected authority in the field, Mr. Hila is dedicated to offering insightful and valuable content that resonates with both vehicle owners and mechanics.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *