how to test ignition coil

by:Haiyan     2023-07-05

Introduction to Ignition Coils

An essential component of a car's ignition system, the ignition coil plays a crucial role in starting and powering the engine. It converts low-voltage electrical power from the battery into high-voltage energy required to create a spark at the spark plugs. A malfunctioning ignition coil can result in a variety of issues, from poor fuel efficiency to engine misfires. Therefore, it is important for every car owner to know how to test an ignition coil. In this article, we will guide you through the process of testing your ignition coil to determine if it requires replacement.

Why Should You Test Your Ignition Coil?

Before discussing the testing procedure, let us understand why it is essential to examine your ignition coil. The symptoms of a faulty ignition coil may not always be obvious, and they can often be mistaken for other issues. Testing the ignition coil will help you identify whether it is the root cause of any engine problems you might be experiencing. Identifying a faulty ignition coil will prevent further damage to your vehicle and save you from unnecessary repairs and expenses.

Understanding the Basics: How an Ignition Coil Works

Before diving into the testing process, it is important to have a basic understanding of how an ignition coil functions. The ignition coil consists of two coils of wire wrapped around a core. The primary coil is connected to the battery, carrying low voltage, while the secondary coil generates high voltage. The interaction between the primary and secondary coils results in voltage amplification, producing the necessary spark to ignite the air-fuel mixture in the engine's combustion chambers.


1. Tools Needed for Ignition Coil Testing

2. Testing the Primary Coil

3. Testing the Secondary Coil

4. Testing for Resistance in the Ignition Coil

5. Interpreting the Test Results

Tools Needed for Ignition Coil Testing

To properly test an ignition coil, you will need a few tools and equipment:

a) Multimeter: Purchase a digital multimeter capable of measuring both resistance and voltage.

b) Insulated Screwdriver: Ensure you have a well-insulated screwdriver to avoid any electrical shocks.

c) Voltmeter: A voltmeter is necessary to measure the voltage output of the ignition coil.

d) Ohmmeter: An ohmmeter will be used to measure the coil's resistance.

Testing the Primary Coil

Begin the testing process by focusing on the primary coil. To test the primary coil, perform the following steps:

Step 1: Switch off the engine and disconnect the ignition coil from the wiring harness.

Step 2: Set your multimeter to measure resistance. Identify the positive and negative terminals on the coil and connect the multimeter accordingly.

Step 3: Measure the resistance. A healthy primary coil typically displays resistance levels between 0.4 to 2 ohms. Consult your vehicle's manual for precise resistance specifications.

Testing the Secondary Coil

After evaluating the primary coil, it is time to test the secondary coil. Follow these steps to perform the test:

Step 1: Reconnect the multimeter, switching the dial to measure voltage this time.

Step 2: Locate the high-tension lead (spark plug wire) and connect the voltmeter to it.

Step 3: Ask someone to crank the engine while you observe the voltmeter. A strong ignition coil will produce a voltage reading of around 12,000 to 25,000 volts.

Testing for Resistance in the Ignition Coil

Another crucial aspect of testing an ignition coil is measuring the resistance. Resistance testing helps identify any damaged or worn-out areas of the coil. Here's how you can perform the resistance test:

Step 1: Disconnect the ignition coil from the vehicle's wiring harness.

Step 2: Set your multimeter to measure resistance and connect the positive and negative terminals to the coil.

Step 3: Compare the resistance reading on your multimeter with the specifications provided by the manufacturer. If the reading is significantly different, the ignition coil may be defective.

Interpreting the Test Results

After completing the tests, it is important to interpret the results accurately. If the primary or secondary coil fails any of the tests, it is recommended to replace the entire ignition coil assembly. Ignition coils are not repairable and should be replaced as a unit.


Regularly testing your ignition coil is vital to ensure the proper functioning of your vehicle's engine. By following the outlined steps using the necessary tools, you can effectively diagnose any issues and determine if your ignition coil requires replacement. Remember, an efficiently functioning ignition coil contributes to optimal engine performance and a smoother driving experience.

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