An ignition coil is an electrical transformer that turns the battery’s low voltage into high voltage needed for firing spark plugs. A failed or worn-out ignition coil can cause a variety of engine-related problems.
Your check engine light flashes or illuminates
The engine control unit monitors ignition coil operation. Once it detects any problems, you’ll see that the check engine light is on.
Poor engine performance or stalling
An ignition coil is the source of high voltage for generating sparks. No voltage means no spark and, as a result, incomplete combustion. For this reason, your engine can misfire, hesitate or even stall when idling.
A poor ignition coil can cause the engine to misfire, which means a lot of fuel will be wasted. This will affect your emissions, so, most likely, you’ll fail the emissions inspection.
Increased fuel consumption
Misfires and incomplete combustion lead to increased fuel consumption, and, therefore, more money will be spent at the pump.
Your engine doesn’t start
If your car is equipped with just one ignition coil, its failure will keep your car from starting. The engine will crank, but won’t start.
What is an ignition coil?
The job of an ignition coil is to transform low voltage from the battery into high voltage, so it can be used for firing spark plugs. Depending on your vehicle, it may have one coil or coil pack per cylinder, or the only coil for all cylinders.
A typical ignition coil features two sets of winding. The first one is called primary winding and consists of hundreds of turns of heavy wires. The secondary winding is a bit lighter as it uses fine wires.
When the engine doesn’t need a spark, the low voltage flows through the primary winding, but once it calls for an ignition spark, the engine control module or the ignition control module cuts the primary circuit, which causes high voltage in the secondary winding. Then this voltage is sent to a spark plug.
The majority of older vehicles came equipped with just one ignition coil located close to the battery. Today’s vehicles feature one coil per cylinder that is mounted on the top of a spark plug. This provides additional advantages and makes modern ignition systems more reliable. Thus, there is no need for high-voltage wires, which means no wire breaks may happen. Besides, it is safer, easier and more energy-efficient to use several coils for generating sparks.
How to fix a bad ignition coil
Once you notice any of the symptoms described above, you should have the vehicle diagnosed by a professional mechanic because sometimes these signs can be caused by other faulty engine parts. Your mechanic will use a special scan tool or an oscilloscope to determine the root of the problem and what needs to be done to fix it. Modern scan tools feature hundreds of integrated scopes which allow for fast ignition system troubleshooting.
A failed ignition coil or pack is not repairable. It must be replaced as soon as possible because it may cause damage to other engine parts, including your catalytic converter.
In most cases, engine coils are easy to access and replace. However, on vehicles with individual coil packs this can be problematic. If so, leave this job to a professional mechanic.
A faulty ignition coil may cause a related spark plug to fail. It’s always a good idea to replace both of them at the same time.
If your owner’s manual provides recommended ignition coil change intervals, follow these recommendations to avoid possible problems in the long run.