22 May 2024
Looking to understand the function of an ignition coil and how to test it for faults? Learn all about it in this informative post. Keep your vehicle running smoothly!

If you’ve ever pondered over the mysterious inner workings of your vehicle’s ignition system, then let’s demystify the role of the ignition coil and how to test it for any potential faults. The ignition coil, a crucial component in the system, is responsible for transforming the low voltage power from your battery into high voltage electricity. This surge of electricity is then directed to the spark plugs, igniting the fuel-air mixture in the engine and ensuring its smooth operation. However, just like any other part, the ignition coil is susceptible to faults. To determine if your ignition coil is functioning optimally, there are a few simple tests that you can perform, ranging from simple visual inspections to more advanced diagnostic techniques. By understanding the function of the ignition coil and how to identify potential faults, you’ll be equipped with the necessary knowledge to keep your vehicle running smoothly.

What is an ignition coil?


An ignition coil is a crucial component of the ignition system in a vehicle. It is responsible for converting the low voltage supplied by the battery into a high voltage that is necessary to create an electric spark in the spark plug. This spark ignites the air-fuel mixture in the combustion chamber, starting the engine.


An ignition coil consists of primary and secondary windings, an iron core, and a casing. The primary winding is connected to the battery, while the secondary winding is connected to the spark plug. The iron core serves as a magnetic conductor, allowing for the efficient transfer of energy between the windings.


The primary function of an ignition coil is to generate a high voltage spark that ignites the air-fuel mixture in the engine’s cylinders. This process occurs through a series of steps. First, the ignition coil receives a low voltage current from the battery. The primary winding then converts this low voltage into a high voltage in the secondary winding through electromagnetic induction. The resulting high voltage is then sent to the spark plug, where it creates a spark that ignites the compressed air-fuel mixture.

Signs of a faulty ignition coil

Frequent misfires

A common sign of a faulty ignition coil is frequent misfires or the engine hesitating or stumbling during acceleration. This occurs when the spark plug does not receive the necessary voltage from the faulty ignition coil, leading to incomplete combustion of the air-fuel mixture.

Decreased fuel efficiency

Another sign of a faulty ignition coil is decreased fuel efficiency. When the ignition coil is not functioning properly, it can result in an uneven spark or weak spark, leading to incomplete combustion. This incomplete combustion requires more fuel to compensate, thus causing decreased fuel efficiency.

Difficulty starting the engine

A faulty ignition coil can also lead to difficulty starting the engine. If the ignition coil fails to generate the required voltage for the spark plug, it can prevent the engine from starting or cause prolonged cranking before the engine eventually fires up.

Testing an ignition coil for faults

Step 1: Visual inspection

Begin by visually inspecting the ignition coil for any signs of damage, such as cracks, breaks, or burn marks. Additionally, check for any corrosion or rust on the connections or casing. Any physical damage or deterioration can affect the performance of the ignition coil.

Step 2: Performing a resistance test

To perform a resistance test, you will need a digital multimeter. Start by disconnecting the ignition coil from the spark plug. Set the multimeter to the resistance or ohms setting and connect the probes to the corresponding terminals on the ignition coil. Compare the resistance reading obtained with the manufacturer’s specifications for the specific ignition coil. Any significant deviation from the expected resistance readings may indicate a faulty ignition coil.

Step 3: Conducting a spark test

Using a dedicated spark tester, connect it to the spark plug wire. Ground the spark tester and start the engine. Observe if the spark tester produces a consistently strong and visible spark. A weak or inconsistent spark may indicate a faulty ignition coil.

Visual inspection

Checking for physical damage

During the visual inspection, carefully examine the ignition coil for any visible signs of physical damage. This includes cracks, breaks, or burn marks on the casing or the insulation. Physical damage can disrupt the flow of electricity and affect the overall performance of the ignition coil.

Inspecting for corrosion or rust

Inspect the connections and casing of the ignition coil for any signs of corrosion or rust. Corrosion or rust can impede the electrical conductivity and weaken the performance of the ignition coil. Clean any corrosion or rust, if present, and ensure proper connections to mitigate any potential issues.

Resistance test

Using a digital multimeter

To conduct a resistance test, make sure to use a digital multimeter. This tool allows for accurate measurement of resistance by applying a small electrical current through the ignition coil.

Determining the expected readings

Refer to the manufacturer’s specifications or service manual to determine the expected resistance readings for the ignition coil being tested. These specifications vary depending on the specific make and model of the vehicle.

Interpreting the results

Compare the resistance reading obtained during the test with the manufacturer’s specifications. If the measured resistance significantly deviates from the expected range, it may indicate a faulty ignition coil. It is important to note that resistance tests are not always definitive, so it is recommended to perform additional tests for a comprehensive diagnosis.

Spark test

Using a dedicated spark tester

For conducting a spark test, it is recommended to use a dedicated spark tester. This device is specifically designed to simulate spark plug firing and can provide accurate results.

Procedure for conducting the test

Connect the spark tester to the spark plug wire and ground the tester as per the manufacturer’s instructions. Start the engine and observe the spark tester for a consistent and strong spark. If the spark is weak, intermittent, or absent, it may indicate a faulty ignition coil.

Interpreting the spark results

A consistently strong and visible spark indicates the ignition coil is functioning properly. However, a weak or inconsistent spark suggests a potential issue with the ignition coil, which may require replacement.

Replacing a faulty ignition coil

Gathering the necessary tools and parts

Before replacing a faulty ignition coil, gather the necessary tools and parts. This typically includes a new ignition coil, appropriate wrenches or sockets for removing and installing the coil, and dielectric grease for ensuring proper electrical connections.

Locating the ignition coil

The ignition coil is usually located near the engine, often attached to the engine block or on top of the cylinder head. Refer to the vehicle’s service manual to locate the specific ignition coil in your vehicle.

Removing and replacing the coil

Start by disconnecting the battery to prevent any electrical shocks. Then, disconnect the electrical connectors and bolts securing the ignition coil. Carefully remove the faulty ignition coil and replace it with the new one, ensuring proper alignment. Reconnect the electrical connectors and bolts, and finally, reconnect the battery.

Precautions while testing and replacing ignition coils

Ensuring proper grounding

Ensuring proper grounding during testing and replacing ignition coils is crucial for personal safety and accuracy of the tests. Use designated grounding points to prevent electrical shocks and to maintain accurate test results.

Disconnecting the battery

Before testing or replacing an ignition coil, always disconnect the battery to prevent accidental electrical contact and potential damage.

Observing safety measures

Take necessary safety precautions while performing tests or replacing ignition coils, such as wearing insulated gloves and eye protection. Work carefully around the engine and follow proper safety guidelines outlined in the vehicle’s service manual.

Seeking professional help

When to consult a mechanic

While tests can help identify faulty ignition coils, it may be beneficial to consult a mechanic if you are unsure or inexperienced in performing automotive repairs. A mechanic has the expertise and specialized tools required for accurate diagnosis and can efficiently replace faulty ignition coils.

Importance of professional diagnosis

Professional diagnosis ensures accurate identification of faulty ignition coils and other potential underlying issues. This can prevent unnecessary replacement of components and save time and money in the long run.

Proper maintenance and care

Regular inspection and cleaning

To maintain the performance and longevity of the ignition coil, regular visual inspection and cleaning are essential. Inspect the ignition coil for any signs of physical damage, corrosion, or rust. Clean any corrosion or rust and ensure all connections are secure.

Replacement intervals

Although the lifespan of an ignition coil varies depending on factors such as driving conditions and vehicle make, it is generally recommended to replace the ignition coil every 100,000 to 150,000 miles or as specified in the vehicle’s service manual.

Using quality ignition coils

When replacing an ignition coil, it is crucial to use high-quality, reliable aftermarket or OEM (Original Equipment Manufacturer) parts. Quality ignition coils ensure optimal performance and minimize the risk of premature failure.

In conclusion, an ignition coil plays a vital role in the ignition system of a vehicle by converting low voltage into high voltage to create a spark that ignites the air-fuel mixture. Identifying signs of a faulty ignition coil, performing tests for faults, and properly maintaining the ignition coil are essential for the optimal performance and longevity of the ignition system. If in doubt or inexperienced, seeking professional help can ensure accurate diagnosis and timely repairs, ultimately keeping your vehicle running smoothly. Remember, regular maintenance and using quality components are key to a well-functioning ignition system.

About The Author