Cause of Ignition Coil Failures

Written by tyler lacoma | 13/05/2017
Cause of Ignition Coil Failures
The iginition coil supplies voltage to the spark plugs. (engine image by Tomasz Pawlowski from

The ignition coil is a system that helps to ignite the gasoline mixture injected into the combustion cylinders in an engine. The ignition system must ignite the fuel in these cylinders very precisely and at a high rate of speed, providing the engine with the energy it needs to function. These coils encounter constant heat and voltage, and can sometimes malfunction or break down through wear.


The ignition coil takes amperage from the battery and ramps it up to a very high voltage to the spark plugs, where it creates the spark that ignites the fuel. Each coil is actually composed of two separate copper wire coils, one large and one small, wrapped around an iron magnetic core. The intense expanding and collapsing electromagnetic fields generated by the coil produce its voltage output.

Coil Insulation

In ignitions coils, the copper wire is wound around the coil hundreds and in many cases thousands of times. These copper wires are insulated so that they do not come in contact with each other as they wind. If the insulation breaks or wears down for some reason and two of the wires touch each other, it will immediately short out the coil and ruin that part of the ignition system.

Spark Plug

Spark plugs are designed to be protected by spark plug caps that keep anything from interfering with the current as it passes through and jumps to the cylinder to create the spark. However, sometimes dust or water can get under the spark plug head and short out the spark system, which will also cause the ignition system to stop working.

Ignition Tower Cracks

Sudden jarring force or heat from other parts of engine can damage the ignition tower itself. The tower is the casing which houses the coils. If this casing is cracked, then it can cause short circuits and allow contaminants to leaks into the coils, which can cause further damage.

Testing Ignition Coil

Sometimes the ignition control system or module can fail, and it can be difficult to tell whether the coils themselves have failed, or the control module is to blame. In these cases, the coil can be detached and tested using a ohmmeter. The leads are placed on the outside prongs of the coil, and the resistance is tested. The coil should show a resistance somewhere between 0.75 and 0.85 ohms. If it does not, the problem is most likely the coil instead of the control module.

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