An ignition coil (also called a spark coil) is an induction coil in an automobile’s ignition system that transforms the battery’s voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel. Some coils have an internal resistor, while others rely on a resistor wire or an external resistor to limit the current flowing into the coil from the car’s 12-volt supply. The wire that goes from the ignition coil to the distributor and the high voltage wires that go from the distributor to each of the spark plugs are called spark plug wires or high tension leads.
Originally, every ignition coil system required mechanical contact breaker points and a capacitor (condenser). More recent electronic ignition systems use a power transistor to provide pulses to the ignition coil. A modern passenger automobile may use one ignition coil for each engine cylinder (or pair of cylinders), eliminating fault-prone spark plug cables and a distributor to route the high voltage pulses. Ignition systems are not required for diesel engines which rely on compression to ignite the fuel/air mixture.
There are several possible symptoms of an ignition coil problem. If your car is experiencing any of the problems listed below, you may have a faulty ignition coil on your hands:
There are many different types of ignition coils that you should be aware of when trying to fix an ignition coil problem. For example, here are three different ignition coil types:
The most common system, with multiple coils, is Coil-On-Plug (COP). There is one ignition coil per cylinder, with each coil connected to the spark plug. If there isn’t enough room for a COP, perhaps because the spark plugs protrude from the cylinder head, then you might have a CNP setup. In this case, the coils would be attached to the plug by short plug wires.
Depending on whether you have a COP or CNP system, you’ll have to check for problems with your ignition coil in different ways, as we’ll detail in the next section.
Testing an ignition coil can be dangerous if done incorrectly. This blog is for informational purposes only. If you do not know how to safely test an ignition coil, you should get help from a qualified specialist.
As noted in the “check engine light” section, you can check for ignition coil problems by running an OBD-II check, which will require an OBD-II scanner. Codes P0300 to P0312 indicate engine misfires, while codes P0350 to P0362 are for ignition coil issues.
For most other kinds of ignition coil tests, you’re going to have to take a look. The location of the ignition coil varies from vehicle to vehicle, so check your vehicle’s user manual or use a search engine to find where your car’s ignition coil is located. Again, take suitable precautions to make sure you don’t electrocute yourself.
Once you’ve found your ignition coil, you can take a look for any obvious signs of damage. The easiest part is checking the ignition coil wiring. If any of the wires are damaged or deteriorated, this could be the source of your ignition coil problems. You should also take a look at the coil harness and connector for faults, especially bent terminal pins and loose connections. If you still can’t find a problem, you can remove each ignition coil from the engine and take a close look for signs of damage. Liquids can damage ignition coils, so pay close attention to signs of moisture.
Ignition coils, sometimes grouped together in a coil pack. If you have problems with your car’s ignition coils, it could affect your car’s performance. This is why it’s important to be alert for the symptoms of a faulty ignition coil, which we’ll run through in more detail now:
Difficulty starting your car’s engine could indicate a problem with your ignition coil. As explained above, most modern engines have multiple ignition coils. If you have several bad ignition coils, you could have a faulty ignition and difficulty starting your engine. Of course, there are a number of different problems that can make it difficult for an engine to start, so difficulty starting the engine alone isn’t enough to confirm an ignition coil problem.
If your engine misfires or stalls when you are idle or when you stop suddenly or accelerate, there could be a problem with your ignition coil. A misfire — which can sound like a coughing or sputtering noise or feel like a jerk or strong vibration — means that one of the engine’s cylinders is not firing correctly.
Misfires are more likely to occur when the engine is under strain, and they can generate emissions. This is why increased emissions and the smell of gas coming from the exhaust are symptoms of a bad ignition coil. As with difficulty starting the car’s engine, there are numerous other issues that can cause misfires that need to be ruled out before you can determine conclusively that the problem is with the ignition coil.
A faulty ignition coil can also cause the car to stall because of irregular sparks sent by the spark plug the faulty coil.
The check engine light is designed to tell you that there’s something wrong with the engine. If you’re driving with an ignition coil problem, your check engine light will pick this up and turn on. You should never ignore the check engine light, but as with the other symptoms we’ve discussed, the check engine light can be caused by a variety of different engine problems.
The easiest way to understand why an engine light is on is with an OBD-II (on-board diagnostics) check. A mechanic will be able to run an OBD-II check for you, or you can run your own OBD-II check using an OBD-II scanner. Codes P0300 to P0312 indicate misfires, while codes P0350 to P0362 are for ignition coil issues.
If you notice that your car is getting less mileage from a full tank than usual, it could mean that you have a bad ignition coil. This happens because, when your spark plugs aren’t getting enough power (due to the faulty ignition coil), the system will try to compensate by injecting more fuel. This also means that fuel leaks can be a symptom of a bad ignition coil.
Poor fuel economy can also be caused by a failing MAF sensor or a dirty engine filter, so these potential issues need to be ruled out as well.
