Bad Ignition Coil Symptoms, Causes, And How To Test it

The ignition coil is one of the most important parts of the gasoline engines. It takes the lower voltage current from the battery and converts it into a higher voltage current that is used to generate the spark. When the ignition coil goes bad, it produces different signs. This article explains the bad ignition coil symptoms, causes, and how to diagnose it.

What is an Ignition Coil?

An ignition coil is an induction coil in a car’s ignition system that converts the voltage of the battery into thousands of volts required to produce an electrical spark in a spark plug to ignite the air-fuel mixture. The ignition coil is also known as a spark coil.

Ignition Coil

Few types of ignition coils contain an internal resistor, while other types depend on an external resistor or resistor wire to control the current flow from the battery of the vehicle into the coil.

The high voltage wires that go from the distributor to each spark plug and the wires that go from the ignition coil to the distributor are known as the high voltage wires or spark plug wires.

The ignition coil has extremely high reliability. However, it may damage due to multiple reasons. The vehicle vibration and heat may damage the coil insulation and winding. This can cause a short or open circuit in the primary or secondary winding. However, voltage overload badly damages the ignition coils. The voltage overload may be due to bad plug wires or a bad spark plug.   

The ignition coil has two sets of windings:

  1. The primary coil windings contain hundreds of turns of heavy wires.
  2. The secondary coil windings contain thousands of turns of thin wire.

Older cars use a distributor and a single coil to deal with all spark plugs. However, the latest vehicles don’t have distributors because they control the ignition coil electronically.

Working of Ignition Coil

The ignition coil contains a laminated iron core and two coils of copper wire. Two copper wire coils are used to surround the laminated iron core. The ignition coil contains two types of windings:

  1. Primary windings
  2. Secondary windings

Working of Ignition Coil

 The ignition coil works in the following way:

  1. As you turn on the car ignition key, the car battery generates a low-voltage current. This current flows from the primary windings to the breaker point and back to the battery. This flow of current generates a magnetic field around the coil.
  2. The secondary circuit contains secondary winding, the spark plugs, the spark plug leads, the distributor rotor, and the distributor cap. When the engine coil turns, the distributor shaft cam also rotates until the high points on the cam cause the breaker points to break swiftly.
  3. When the contact opens in the contact breaker, the current in the primary winding breakdowns, this also destroys the magnetic field in the core. This unexpected breaking of the magnetic field creates a very high voltage (i.e., 50,000 volts) in the secondary windings.
  4. This high-voltage current is then delivered to the spark plug via the distributor to create an ignition spark.

Symptoms of A Bad Ignition Coil

When the ignition coil goes bad, it produces one or more of the below-given symptoms:

  • Poor Fuel Economy
  • Backfiring
  • Check Engine Light
  • Poor Engine Power
  • Spluttering and Coughing Sounds
  • Hard to Start
  • Vehicle Stalling
  • Excessive Vibration

1) Poor Fuel Economy

Poor fuel economy, symptoms of bad ignition coil

A reduction in the vehicle fuel economy is one of the famous signs of a bad ignition coil. When the ignition coil is damaged, it doesn’t supply power to the spark plug according to its requirement due to that vehicle’s engine works hard and consumes more fuel than usual.  

2) Backfiring


The vehicle backfiring is an initial sign of the ignition coil failure. The backfiring occurs when the engine expels unused fuel from the exhaust pipe. The vehicle may face backfiring issues due to some other reasons, such as engine oil leaks, coolant leaks, or a bad head gasket. 

When you notice a vehicle backfiring issue, immediately inspect and fix the issue; otherwise, it can result in serious damage to the exhaust, which can lead to avoidable and expensive repairs.

3) Check Engine Light

check engine light

If the car stalls or is difficult to start, the check engine light will illuminate. As the ignition coils become faulty, the powertrain control module (PCM) of your vehicle activates the check engine light along with a fault code like P0351, P0352, P0353, or P0354.

However, the check engine light may illuminate due to some other reasons, such as a bad radiator, insufficient coolant, low oil level, or blown head gasket.

Read  More: Causes of Check Engine Light Illumination

4) Poor Engine Power

Reduced engine power, signs of bad ignition coil

The reduction in engine power is one of the main symptoms of a bad ignition coil. When the ignition system goes bad, the ignition coils don’t deliver sufficient power to the spark plug; due to that, it doesn’t produce a powerful spark.

When the plug doesn’t produce a spark according to requirements, the air-fuel mixture inside the combustion chamber doesn’t burn efficiently.

When the air-fuel mixture doesn’t burn efficiently, you will see a reduction in the engine power, and the car slows down. In the event of a power outage, drive your vehicle to a mechanic and fix the problem.

5) Spluttering and Coughing Sounds

Coughing Sound

When starting the engine, a bad ignition coil may generate a stutter or cough sound. This sound comes from a cylinder in which the air-fuel mixture is not igniting properly during the ignition process.

6) Hard to Start

Hard Starting condition

In order for the engine to start and the car to run, the spark plug must generate a spark at the right time. When the ignition coil goes bad, it doesn’t supply the desired power to the spark plug to generate a spark; due to that, the engine will be hard to start.

Read More: Reasons Why Car Starts Then Dies?

7) Vehicle Stalling

Vehicle Stalling, symptoms of a faulty ignition coil

Ignition coil failure can cause the vehicle to send an irregular spark to the spark plug, causing the vehicle to stall. As the vehicle stalls, it can be forced to shut down completely and restart.

Read More: Engine Stalling Causes and Preventions

8) Excessive Vibration

Vehicle vibration is one of the common symptoms of ignition coil failure. You may also notice that your vehicle jerks forward as you increase its speed.

 Causes of A Bad Ignition Coil

The following are the major causes of a bad ignition coil:

  • Damaged or Worn Spark Plugs
  • Engine Overheating
  • Vibration
  • Wear and Tear
  • Poor Maintenance
1) Damaged or Worn Spark Plugs

As the spark plug wears out, the ignition coil starts to work at higher power. To prevent the ignition coils from being damaged, you must maintain the spark plug in good condition.

When the spark plug wears out, the gap between each plug widens. That means the coil has to deliver a higher voltage than usual to fill the gap. This extra stress on the ignition coil can cause a voltage surge that can overheat and eventually fail.

Read More: Bad Spark Plug Symptoms and Causes

2) Engine Overheating

Engine overheating is one of the most common causes of ignition coil damage.

Excessive heat can impair the conductivity of an ignition coil, leading to reduced electrical conduction. Repeated exposure to high temperatures and heat cycles can accelerate the degradation of the ignition coil beyond normal rates.

The consequences of an overheated ignition coil can result in the complete malfunction of the vehicle’s ignition system.

Read More: Engine Overheating Symptoms and Causes 

3) Excessive Vibration

Vibration can damage the ignition coil windings and insulation and cause short circuits or damage to the secondary windings.

4) Wear and Tear

Wear and tear is a common cause of ignition coil failure. The wear & tear degrades the insulation between the secondary and primary coil windings and the primary coil. Poor insulation can cause the coil to overheat.

5) Poor Maintenance

Lack of regular maintenance, such as failing to replace spark plugs, ignition wires, or other related components, can put additional strain on the ignition coil, leading to its deterioration.

Ignition Coil Location

The placement of the ignition coil in a vehicle varies depending on your specific make and model. Generally, ignition coils are located in areas of the engine that are subjected to high vibrations, temperatures, and dirt accumulation.

Ignition Coil Location

A common location for modern ignition coils is between two camshafts on the valve cover, which exposes them to oil and dirt in the engine compartment. These conditions produce extreme challenges to the durability and performance of the ignition coils.

How to Test an Ignition Coil?

To test or diagnose the ignition coil of your vehicle, follow the below-given steps:

  1. Inspect the ignition coils of your vehicle for visible damage, like leaks or cracks. If any damage is detected, it is recommended to replace the ignition coil.
  2. Connect an OBD2 scanner to the OBD-II port of your vehicle.
  3. Verify that the trouble code corresponds to an issue with the ignition coil. If it does, switch off the engine and let it cool down.
  4. Gently detach the ignition coil from the engine cylinder indicated by the trouble code and exchange it with a coil from another cylinder.
  5. Start the engine and carefully monitor the error codes.
  6. If the new cylinder shows a misfire error code while the previous cylinder does not, it indicates a faulty ignition coil that needs to be replaced.

Frequently Asked Questions

What is the function of the ignition coil function?

The ignition coil works very similarly like a transformer. With two-layered coils, the ignition coil takes electrical energy from the vehicle battery and converts it into a high voltage. This high-voltage power is transferred to the spark plug, which uses this voltage to generate a high-voltage spark. 

What are the applications of the Ignition coils?

The ignition coils are most commonly used in the petrol engines such as cars, motorcycles, buses, tractors, etc.  

What are the parts of the ignition coil?

  1. Iron core
  2. Primary Winding
  3. Secondary Winding

How to identify failure of Ignition Coil?

When the ignition coil of your vehicle becomes faulty, it produces different symptoms such as backfiring, engine shaking, stalling, engine misfiring, poor fuel economy, check engine light illumination, or poor engine performance.

How often do I have to replace ignition coils?

Ignition coils are generally planned to last around 100,000 miles, but certain reasons, such as moisture, heat, and high voltage from faulty spark plugs, may accelerate their deterioration. Early coil pack failure can lead to different problems, such as misfires and reduced fuel economy.

Can I drive a Car with a bad Ignition Coil?

Yes, it is possible to continue driving with bad ignition coils in some cases, but it is strongly discouraged to do so for a long time. Ignoring an ignition coil issue can potentially lead to damage to the catalytic converter, which can be a costly component to change.

How long can you drive with a bad ignition coil?

It is not recommended to drive with a bad ignition coil for more than 100 km. Continuing to drive with a malfunctioning coil can strain the engine as it runs on fewer cylinders. The latest vehicles are equipped with a PCM or ECM system that can halt the delivery of fuel to the affected cylinders, resulting in unburned fuel accumulating in the exhaust.

Can a bad ignition coil damage engine?

Backfiring is characterized by a loud bang. However, backfiring is generally not expected in the latest engines. However, if backfires do occur, a bad ignition coil is among the common culprits. It’s important to address backfiring promptly, as it may potentially result in severe engine damage.

What is the sound of a bad ignition coil?

If you notice coughing or spluttering noise during engine startup, it is likely that an ignition coil is the cause of the issue. These noises originate from the engine cylinders that fail to ignite fuel properly during the ignition process.

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