Bad Or Failing Ignition Coil Symptoms

Brandon Trenton

Bad Or Failing Ignition Coil Symptoms

If your car is giving you a hard time, then there might be a problem with its ignition coil. Ignition coil works like a transformer, converting low voltage energy from the car battery into high voltage and providing it to the spark plug. This lights up the air-fuel mixture in the cylinder producing power.

If you try to start your engine, but the only thing you are hearing is a spluttering sound, again and again, or your car is low on power while you try to speed up on the highway, then you are most likely experiencing the signs of the bad ignition coil.

How Does Ignition Coil Works?

Ignition System

Ignition coil lies inside the ignition system. The ignition system is like a circuit consisting of ignition switch, coil, contact points, condenser, spark plugs, cables, and distributors powered up by a lead-acid battery. The coil solely doesn’t perform the grand hassle of transforming the low voltage current into a higher one from the battery. Usually, a car battery has a potential of 12V. You would be amazed to know that the spark plugs need around 20K to 40K volts to keep your car moving. Now that you know that this energy step-up is such a big deal as they are amplifying energy 1000 times, you can coil this little guy as a compact transformer.

Two Winding That Surround the Iron Core

The ignition coil got two windings that surround the iron core; one is called primary while the other is called secondary. Usually, the coils are safe inside a covering. Oil is added to it to keep it cool.


The primary one has a low voltage current and forms the outer coil.


Whereas, the secondary winding transforms that low current into a higher one. You can tell the difference between them with the number of turns. Secondary one definitely has more. This works as a framework turning it into a step-transformer.

Induction of High Voltage Current in Secondary Coil

When the battery supplies voltage to the primary coil, it creates an electromagnetic field. Then, upon rotation of the coil, the current stops flowing, breaking up the magnetic field. This results in the induction of high voltage current in the secondary coil, which is transmitted to the spark plug or distributor, sometimes.

How Would You Know That The Ignition Coil Has Gone Bad?

1. Car Backfiring

You will hear a loud noise from the motor engine. Yes! That’s a backfire coming out of explosion from the engine during internal combustion. This could even take place in the exhaust. When the ignition coil is not working properly, the voltage received by the spark plugs is not enough to produce complete internal combustion. This leaves unused fuel behind that travels through the exhaust later.

This fuel explodes before coming out, causing severe damages to the system in the not so distant future. Spark plugs can also result in such problems if they aren’t functioning properly or the fuel-air mixture is too dense.

If your car emits black smoke, then it is the sign. You can further be sure if you smell strong gasoline produced by a random explosion coming out of the exhaust. It may also produce fire. This is a grave concern, and you need to take your car to the service center to save yourself from expensive problems.

2. Engine Misfiring or Stalling

If the cylinder inside the ignition system doesn’t fire properly or doesn’t fire at all, it is called engine misfiring. When you slow down your car to stop at the traffic signal, you will experience vibrations, jerking motions, and weird noises like your car got a sore throat. Yes, the ignition coil has messed up. Malfunctioning of sparkplugs, plug wires, and fuel delivery system can also make the engine misfire.

There is no time limit for this to happen. It can take place anywhere and any minute. However, if you have been driving your car for long or for any reason your engine is on load, this could be a reason, too. The bad news for you is that the emissions produced during the firing could damage other parts, for example, the catalytic convertor. This might also damage the fuel-air mixture sensors, disturbing internal combustion and creating further problems, especially when you want to speed up.

If it goes unrecognized, then the situation would become worse, and your car will stop right at the spot where it is. You can face it when you are starting your car and trying to increase its speed or when you stop, and the engine shuts off or while slowing down or changing gears too fast. Transmission problems, the fuel delivery system, the idle air control actuator, and a clogged EVR value is another area to look into for a stalling or misfiring engine.

3. Bad Fuel Mileage

If you have been driving a car for a while, then you can easily determine its fuel economy. However, for some days, if you are witnessing more fuel consumption, this is a sign of a bad ignition coil. The sparks need enough power to function, that doesn’t happen when the ignition coil has gone bad. Now spark plug got no option but to use more fuel to deliver the same power.

Fuel leakage due to a worn-out fuel injector can be another cause. The time when an ignition coil is not working properly, the oxygen sensor becomes faulty as well. They don’t detect the right amount of fuel required and deliver more fuel than required.

4. Hard-Starting Engine

This usually happens in a car with a single ignition coil. Here, your whole car engine depends upon a single ignition coil, and if that wire wears out, then the whole system will be affected. However, a single coil is not the only culprit. This could happen even if one of the spark plugs doesn’t receive the right amount of power. As a result, you wouldn’t be able to start your car.

 If you start your car and still hear a clicking sound, this means the coil still functioning. However, a bad ignition coil will not produce any energy at all that could light up the internal combustion to start.

5. Check for the Engine Light

There is a light inside your car to keep a watch on the engine functionality. If you find that on, this means the ignition coil has gone bad. You should take your car to the mechanic for inspection in this case. They will carry out an OBD-II check. If you can purchase an OBD-II scanner online or an automotive store near you, then you can even do it yourself. The possible codes that you may get as a sign of misfiring would range between P0300 to P0312. Standard diagnostic trouble codes (DTCs) for poor ignition coil circuit working range from P0350 to P0362.

6. Oil Leaks

A malfunctioning ignition coil could result in overheating. Overheating damages the covering of the coil, resulting in tears. This tear results in leaking oil. Again, leaking oil doesn’t only result from the housing of the wire coils. The gap in the spark plugs can also cause it. These bigger gaps are often a result of erosion. Now the ignition coil will work at a higher voltage, and as a result, the coil overheats and leaks oil after breaking.

Types of Ignition Coils


The ignition coil, along with the distributor, forms the distributor system. This type is the oldest one in use since the 1900s. The primary coil receives power from the battery. It stops rotating as the distributor cam breaks the connection suddenly. Now the secondary coil induced to produce a higher voltage.


This type of coil work just like the conventional coil. Here the rotation of the coil is stopped by the intervention of electronic system in place of a distributor cam for sending voltage to the ignition system for starting it. You would have found it in every car belonging to the 1970s.


There is a single coil for every two cylinders. It comes in a bundle or as a unit having some coils together. The difference in its mechanism is the use of a magnetic device for changing the speed.

Coil on Plug:

Each spark plug is supported by two coils in this system. It works on the electronic system like one in the electronic type.

How to Test an Ignition Coil?

Want to know if the ignition coil of your automotive has failed or not, this is the right way to go about it:

  • Once the car is turned off, open its hood. You will have to locate the ignition coil first. Dependent on the vehicle model, its location is bound to differ. The Internet should be able to give you near to accurate answers.
  • Start with removing wires from the spark plug.
  • Then, remove the spark plug. It’s ideal to do it with a spark plug socket.
  • Attach the wire back to the spark plug, cautiously.
  • You’d be able to see the threaded portion of the plug. Touch it to any exposed metal on the car.
  • Remove the fuse or the fuel pump relay.
  • You should have someone to help you. Ask them to turn the infusion key for you.
  • You will see a blue spark between the threaded head and the metal part that you are touching. This is a sign that the ignition coil is working.

How Can you Prevent a Bad Ignition Coil?

Pay Attention to the Ignition System

You need to follow rather easy steps to keep your car healthy. Need to take care of the ignition coil? Pay due attention to the ignition system. Keep the plugs good. You can’t imagine how much money they can save you for repairs in the future. Check the plugs in case they’ve worn out, owing to the normal use or may have eroded.

Check the Ignition Coil

Check if the ignition coil is doing fine or not. The housing should be in prime condition and shouldn’t essentially leak any oil. For your ignition system: the wires should also not be in bad shape or either toasted. Don’t forget, you need to apply all other maintenance recommendations by your vehicle manufacturer as well.

Look Out for Bad Ignition Coil Symptoms

Do you know what a bad ignition coil can do? Engine misfire, backfiring, oil leakage, poor fuel consumption, the engine lights turning on, and vehicle stalling, etc. For someone, which takes due care, these issues with the ignition system should not arise in conclusion.