5 Signs You Need An Ignition Coil Replacement

Here are some common signs of a faulty ignition coil:

1. Misfiring Engine

A bad ignition coil may cause your car to misfire while accelerating or, worse, stop your car while driving.

A misfire happens when a failing ignition coil generates an inconsistent voltage, affecting the spark plug and the combustion. As a result, a cylinder may fire incorrectly — causing spluttering or coughing noises.

Note: Misfires can affect the engine performance and damage engine components like the catalytic converter. So get your car checked out if your engine misfires.

2. Trouble Starting The Car

A failed ignition coil doesn’t deliver the required voltage for spark plugs to ignite the air and fuel mixture. As a result, you may find it difficult to start your car if multiple coils malfunction. 

Car starting issues are common for many malfunctions, including a poor ignition coil connection or an electronic control module (ECM) issue. To confirm, get your car checked out by a mechanic.

3. Rough Idling

Bad ignition coils can also cause your car to run unsteadily at different RPMs (revolution per minute), even without your foot on the gas. 

Sometimes, your car may have tiny vibrations when parked. These vibrations are gentler than misfires; however, they can shut down your running car in severe cases.

All of this is due to a bad coil generating power at irregular intervals — causing the fuel to burn inconsistently.

So, RPM fluctuations while driving or unusual engine sounds can point to ignition coil failure.

4. The Check Engine Light Turns on

Another sign of a bad ignition coil is the Check Engine light. It often illuminates when there’s a faulty ignition coil. 

Remember that the Check Engine light can light up for many reasons, like a bad catalytic converter, a bad spark plug, or a loose fuel cap. So if your car supports the OBD 2 system, use an OBD 2 code scanner or a multimeter to confirm what’s wrong. 

If it’s an ignition coil issue, it’ll likely read engine light codes from Code P0350 to Code P0362, depending on the faulty cylinder in your car. 

For example, if there’s an issue in your first cylinder’s ignition coil or circuit, the OBD 2 code scanner will read Code P0351 (Ignition Coil ‘A’ Primary/Secondary Circuit Malfunction). 

Note: The OBD 2 scanner will read other codes too (if any) that aren’t related to the ignition coil.

5. Increased Fuel Consumption

One of the early signs of an ignition coil failure is increased fuel consumption.

A faulty coil won’t be able to create enough electric spark for the spark plugs, resulting in reduced engine power. So to compensate, the car injects more fuel into the combustion chamber,  affecting your gas mileage. 

Note: Fuel consumption is difficult to spot. To identify significant changes, you can drive your car at regular intervals and distances. Or just call a mechanic if you suspect increased fuel consumption.

How Much Does It Cost To Replace Ignition Coils?

The ignition coil replacement can cost around $60–$350. This includes spare parts like the replacement ignition coil ($30–$150) and labor costs ($30–$200). You can also get a spark plugs replacement done if required — saving money and time.

Note: The ignition coil replacement cost can vary according to your location, car model, etc.

How Urgent Is An Ignition Coil Replacement?

A new ignition coil is meant to last for approximately 100,000 miles. But it can get damaged at any time due to a bad spark plug, engine heating, or vibrations.

Faulty ignition coils can shut down your car while driving — making it hazardous to drive, especially in busy traffic.   

Moreover, it can damage other vehicle parts, such as the engine or the catalytic converter. 

That’s why it’s vital to get your car checked out at the slightest sign of a failing ignition coil — especially since they don’t usually last long after the first symptoms.

3 Ignition Coil FAQs

Here are some important things to know about ignition coils:

1. What Is An Ignition Coil?

The ignition or the spark coil is an essential part of the ignition system. It acts as a compact transformer — converting the low voltage (12 volts) from the battery to a higher voltage needed to create an electric spark in spark plugs.

The number of ignition coils varies according to the car — although most modern cars have multiple coils instead of a single ignition coil system.

Ignition coils can be mounted on spark plugs or placed nearby in a coil pack with ignition cables connecting them to individual spark plugs. Traditionally, the coils were either found with distributors or placed nearby to send sparks to the distributor. 

But today, many modern cars, whether a Honda, Nissan, or Hyundai, have an ECM in the engine instead of distributors. 

The ECM commands the ignition coils, helping the spark plug fire precisely according to the piston and valve movement. This improves engine performance, offering better fuel economy and reduced emissions.

2. How Does An Ignition Coil Work?

The ignition coil (spark coil) is an induction coil that produces a high voltage from a low voltage. The resultant high voltage creates an electric spark for the spark plugs.

Now, this induction coil consists of two individual coils — a primary winding (200-300 turns) and a secondary winding (20,000-30,000 turns). 

A magnetic field is created when the primary coil is exposed to 12 volts of electricity from the car battery. When the spark plug needs a spark — the ignition system stops the current to the primary coil. 

Since the magnetic field and electric current are linked, the magnetic field collapses when the primary winding stops receiving the current. 

However, the secondary coil can create electric current from the collapsed magnetic field, as magnetic fields can store energy. Since the secondary coil has more windings, the generated voltage is amplified enough to fire the spark plugs and start the car.

3. How To Replace The Ignition Coil?

An ignition coil replacement requires you to have basic auto repair knowledge. So it’s best to contact a mechanic or auto repair shop to replace your failed ignition coil. 

With that said, here’s a DIY guide on ignition coil replacement:

1. First, disconnect the battery using a socket and ratchet to cut power to the vehicle.
2. Locate and check which faulty coil needs a replacement with a multimeter.  
3. If there’s more than a single coil, label the ignition cables from the individual coil left to right. 
4. Now disconnect each cable slowly and tuck it to the side to access the bad coil easily.
5. Once done, release the electrical connector from the side of the ignition coil. 
6. Next, unbolt the screws and remove the faulty coil from the engine bay using a wrench.
7. Install the new ignition coil, along with the screws and the electric connector.
8. Finally, replug the ignition cables and reconnect the car battery.

Start the car to test the new coil. If it doesn’t crank, the battery is dead or not connected properly. If the car turns over but fails to start — recheck the new ignition coil for proper connectivity.