how to know if your ignition coil is bad

by:Haiyan     2023-06-24

It is imperative for vehicle owners to be aware of the signs of a faulty ignition coil as it directly impacts the overall functioning of their cars. Ignition coils are responsible for providing the necessary voltage to power the spark plugs, which ignite the fuel in the engine. Without a healthy ignition coil, a vehicle's performance and fuel efficiency can suffer. In this article, we will discuss the key indicators of a bad ignition coil and offer insights on troubleshooting and replacing the faulty component.

Signs of a Faulty Ignition Coil

1. Engine Misfires and Rough Idling

One of the most common indicators of a bad ignition coil is frequent engine misfires. As the coil delivers voltage to the spark plugs, a faulty coil can disrupt this process, causing the engine to misfire or operate irregularly while idling. You may notice your vehicle vibrating or shuddering during idle, which can even result in stalling if the problem worsens.

2. Difficulty Starting the Engine

A problematic ignition coil can lead to difficulties starting your vehicle. If you regularly experience prolonged cranking before the engine starts, it could be a sign of insufficient voltage reaching the spark plugs. While other factors can contribute to engine starting issues, it is worth inspecting the ignition coil as a potential culprit.

3. Decreased Fuel Efficiency

A failing ignition coil can negatively affect your car's fuel efficiency. If the coil is unable to provide a consistent and steady voltage to the spark plugs, the engine may not be able to ignite the fuel-air mixture efficiently. As a result, your vehicle may consume more fuel than usual, reducing overall mileage.

4. Engine Stalling or Power Loss

When an ignition coil is faulty, you may experience engine stalling or sudden power loss while driving. The engine may shut off abruptly, leaving you stranded. If this occurs, it is crucial to have your vehicle inspected by a qualified mechanic to diagnose the problem accurately.

5. Illuminated Check Engine Light

A check engine light that stays on or flashes intermittently can indicate a faulty ignition coil. Modern vehicles are equipped with onboard diagnostic systems that monitor various engine components, including ignition coils. If the system detects irregularities in the ignition coil's performance, it will trigger the check engine light. You should use an OBD-II scanner to retrieve the specific error code and identify the problematic coil.

Troubleshooting and Replacing a Faulty Ignition Coil

If you suspect a faulty ignition coil based on the signs mentioned above, there are several steps you can take to troubleshoot and potentially replace the component.

1. Conduct Visual Inspection

Start by visually inspecting the ignition coil. Look for any signs of physical damage, such as cracks, corrosion, or oil-soaked insulation. Any visible damage may indicate a need for replacement.

2. Perform Coil Resistance Test

Using a multimeter set to the ohms () setting, you can perform a resistance test to check the coil's electrical continuity. Consult your vehicle's service manual or reputable online sources for the specific resistance values for your particular coil. If the measured resistance deviates significantly from the acceptable range, the coil may be faulty and require replacement.

3. Test Spark Plug Wires and Connections

Ensure the spark plug wires are securely connected to both the ignition coil and the spark plugs. Loose or damaged connections can interfere with the ignition process, resulting in poor performance. Test the spark plug wires' resistance using a multimeter to ensure they are within the manufacturer's specified range.

4. Replace the Faulty Ignition Coil

If the troubleshooting steps confirm a faulty ignition coil, it is time to replace it. Consult your vehicle's service manual for the appropriate removal and installation procedures. In most cases, it involves disconnecting the electrical connectors and removing mounting bolts. Replace the old coil with a new one and reassemble the components.

5. Recommended Maintenance and Expert Assistance

To prevent ignition coil problems in the future, follow the recommended maintenance intervals provided by the vehicle manufacturer. Regularly inspect and clean connectors, check for any signs of wear or damage, and replace them as necessary. If you are unsure how to troubleshoot or replace a faulty ignition coil, it is advisable to seek professional assistance from a qualified mechanic.


Faulty ignition coils can significantly impact your vehicle's performance, fuel efficiency, and drivability. By understanding the signs of a bad ignition coil and following the troubleshooting steps provided, you can identify and rectify the issue promptly. Remember, regular maintenance and timely replacement of ignition coils are essential for keeping your vehicle running smoothly.

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