The Symptoms of Ignition Coil Failure. Ignition coils are an important component of modern car ignition systems. Since the 1990s, most engines have used electronically-controlled ignition rather than distributor ignition systems. einsteinerupload of.
While this is the most common type of ignition system today, some vehicles still use distributor-less electronic systems that use a single master ignition coil to distribute power to all spark plugs via spark wires.
There are several types of ignition coil setups:
- Coil-on-Plug (COP) : systems have the ignition coil directly on top of the spark plug in the cylinder. Every cylinder and spark plug has its own coil.
- Coil-near-Plug (CNP) : It is not always possible to place the ignition coils directly on the spark plug. In this case, the ignition coils are disconnected from the plug and connected by spark plug wires.
- Coil-per-Cylinder (CPC): Coil-per-cylinder systems can be either COP or CNP, but they only use one ignition coil per cylinder. As an alternative to CPC systems, some modern ignition systems will use one coil to power two cylinders.
When available, coil-on-plug systems are the best option because they eliminate the need for spark plug wires, which adds another potential failure point to the ignition system.
Coil packs are another name for ignition coils. While coil packs technically only refer to ignition coils that are physically grouped together, we will use the terms interchangeably throughout this article.
What Exactly Are Ignition Coils?
Engines require combustion to start and maintain operation. Air, fuel, and spark are the three main components of combustion. While spark plugs generate the actual spark, they require electrical current to do so.
A spark plug requires thousands of volts of electricity to ignite. Car batteries are typically only 12-volt batteries, which fall far short of the voltage required for a spark plug to fire.
Electrical transformers are what ignition coils are. The ignition coils receive voltage from the battery and convert it from 12-volts to the tens of thousands of volts needed for the spark plugs to function properly.
How Do Ignition Coils Function?
Inside a spark plug is a coil of wire that serves as a conductor. To circulate electrical currents through the wire coil, a circuit switch opens and closes.
When the switch is turned on, current flows through the coil’s windings. This causes a magnetic field to form around the coil, amplifying the voltage of the electrical current. The switch is then closed, causing the magnetic field to collapse back into the coil and be transferred to the spark plug.
Nowadays, most ignition coils use a two-coil wire system. The first coil generates a magnetic field that can be 10x-20x the initial 12-volt voltage. The second coil wire is more compact and, as a result, generates more voltage through the magnetic field, resulting in a 100x increase in voltage and the ability to exceed 20,000 volts.
Check out Denso’s technical writeup on how ignition coils work if you want to get into the nitty gritty.
Symptoms of a Faulty Ignition Coil
- Misfires in the cylinders
- Beginnings are difficult.
- Idling in a rough manner
- Hesitation or stuttering while accelerating
- Exhaust causes a backfire
- Engine light on (codes for misfires)
- Fuel economy is deteriorating.
Misfires are the most noticeable symptom of a bad ignition coil, especially under acceleration. When an ignition coil fails, it does not provide enough voltage to the spark plug to spark. This causes gasoline to accumulate in the cylinder, where it can detonate due to heat at an inopportune time, resulting in a misfire.
Misfires will cause the engine to jerk or hesitate. Misfires will usually appear from time to time, and once the coil has deteriorated further, they will become very frequent. If only one ignition coil fails, you will most likely not have any starting problems; however, these can occur if multiple fail at the same time.
For misfires, most vehicles will generate P0300-P0312 engine codes. The specific code will indicate which cylinder is malfunctioning. Some vehicles will generate codes related to the ignition coils, which are typically P0350-P0362.
The symptoms of a bad ignition coil are nearly identical to those of a bad spark plug. Before purchasing and installing a new set of ignition coils, make sure you remove and inspect your spark plugs. Because the symptoms are similar and spark plugs are relatively inexpensive, most people replace them at the same time as the ignition coils.
Ignition Coil Testing
The first and foremost check should be inspecting the coils themselves. They are probably bad if they have cracks, burn marks, are melted, or are coated in oil. If the coils appear to be in good condition upon visual inspection, try the following methods for testing ignition coils:
1) Coil Swapping
The simplest way to determine whether your problems are caused by spark plugs or ignition coils is to swap the ignition coils.
For example, if you receive an engine code for a cylinder 2 misfire, replace the cylinder 2 ignition coil with the cylinder 1 ignition coil. Clear the engine codes and drive the vehicle until another misfire occurs, then check the engine codes again. If the misfire code now indicates cylinder 1, the ignition coil is faulty. If you use this method and the engine code still says cylinder 2 is bad, it means your spark plug is bad (or there is another problem).
For cars that use spark plug wires, use the same procedure but swap the wires instead. Just make sure you don’t swap the ignition coil with it otherwise you won’t be sure if it is the wire or the coil that is bad.
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2) Making Use of a Multimeter
If swapping coils isn’t an option, testing the ignition coil’s coil wires for Ohms resistance is the next best thing. Purchase a multimeter and connect the positive and negative leads to the appropriate coil wire terminals. You must measure the ohms of both the primary and secondary windings.
Depending on how it was manufactured, each ignition coil will have different touch points. Check your owner’s manual or a Haynes repair book for the proper coil touch points and Ohm ranges for each coil winding.
Because ignition coils operate differently under load versus no load, this method may produce incorrect results.
3) Additional Testing Options
The two options listed above are your best bet. We prefer Methodology #1, but it can be time consuming if you also have spark plug wires and need to perform multiple swaps to diagnose the problem.
There are more advanced ignition coil testers and inline spark testers, as well as more expensive newer coil-on-plug testers that allow you to test coils without removing them from the vehicle.
Cost of Ignition Coil Replacement
This isn’t true for every car, but for most modern vehicles, any average Joe with the right tools can swap out the spark plugs and ignition coils.
When replacing ignition coils, you have two options: replace only the bad ones or replace all of them. Most people like to swap them all out at the same time, but this becomes more costly especially for people with V8 or larger engines.
Also, if you intend to have them replaced at a repair shop, replacing them all at once will save on labor costs because the majority of the time it takes to replace them is getting to them in the first place.
Costs of Replacing a Single Ignition Coil
- Parts: $20-$40
- Labor: $80-$150, or roughly one hour of labor costs
Costs of Ignition Coil Set Replacement
- Parts: $100-$400 (cost increases as engine gets bigger ie. inline-4, V6, V8)
- Labor costs: $120-$250, or approximately 1.5 hours of labor.
Spark Plug Wires vs. Ignition Coils
Spark plug wires will be used in vehicles that do not have coil-on-plug systems. Ignition coils generate the voltage needed by spark plugs, and plug wires carry that current from the coil to the spark plug.
Because the wires are in charge of carrying the voltage, faulty wires will exhibit the same signs and symptoms as faulty ignition coils. These are also commonly replaced at the same time, but if you just want to swap out the bad culprit, use our testing methods above to determine if it is the coils or wires causing the issues.
Cars without spark plug wires will have a coil-on-plug setup, in which the ignition coil connects directly to the spark plug head, eliminating the need for transport wires and reducing a potential failure point.