5 Symptoms of a Bad Ignition Coil (And Replacement Cost)

An ignition coil in a vehicle basically serves as a compact electrical transformer. In other words, an ignition coil has the ability to convert the 12-volt electrical current from a car battery into at least 15,000 volts of electricity for the spark plug.

This high-voltage current gets sent to the spark plug and then the spark plug is able to ignite the fuel so that the engine can start up.

There is one ignition coil for each spark plug. In some vehicles, the spark plug and ignition coil are connected together with wires, while other cars will just have the ignition coil positioned above the spark plug without the need for wires.

Either way, you need good ignition coils in order to ensure the engine starts up fine. Otherwise, having a faulty ignition coil will make your vehicle susceptible to misfires and cause an increase in the amount of fuel being consumed.

Related: Common Symptoms of Faulty Spark Plugs

Top 5 Bad Ignition Coil Symptoms

If you are experiencing any driving problems related to the combustion process in the engine, you could possibly have a bad ignition coil. The exact symptoms are dependent on how bad the condition of the ignition coil actually is.

Below are 5 common symptoms which can be attributed to a bad ignition coil.

1) Stalling

engine stall

If your vehicle begins to stall as you’re driving, it could be related to your ignition coil being bad. Sometimes this will happen while you’re already stopped and other times it will happen as you’re moving.

If the coil is just starting to go bad, it will send irregular electrical currents to the spark plug. That is why you could be driving normally and then suddenly experience problems later.

Once you are moving and the stalling starts, it will eventually lead to you stopping completely and not being able to start back up.

2) Engine Misfiring

engine misfire causes

If you try to start your engine up and you hear a spluttering sound repeatedly, then you are likely experiencing an engine misfire that can be attributed to a bad ignition coil.

You may still be able to drive your vehicle, but you will hear a lot of strange noises and even feel your car jerk when accelerating.

3) Bad Fuel Economy

signs of bad gasoline

When there is a bad ignition coil and there are engine misfires because of it, then an increase in fuel consumption is likely going to follow.

As a result, you will have reduced mileage from your gas tank and you will need to fill up your tank more often. This means you will be spending a lot more money on gas than you normally did before.

4) Backfiring

black smoke from exhaust

At the beginning of having ignition coil problems, your vehicle will experience a backfiring problem. This is a term that refers to a situation where the internal combustion cylinders have unused fuel left in them and it ends up flowing out of the exhaust pipe.

The first sign of this will be black smoke pouring out of the exhaust pipe. This smoke will have a gasoline smell to it as well.

5) Check Engine Light

oil pressure check engine light

Since a bad ignition coil directly affects the functionality of the engine, then you can expect the check engine light to illuminate on your dashboard. There are even some vehicles out there which only have one ignition coil and spark plug.

So, without at least one working ignition coil, the cranking of the engine will occur when there are no sparks being generated inside the cylinders. Of course, a check engine light can mean any number of things wrong with your vehicle.

But if you have experienced any of the previous four symptoms listed above and then you have a check engine light on too, then the ignition coil is likely to blame.

Ignition Coil Replacement Cost

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ignition coil replacement cost

The average cost of a single ignition coil is going to be around $100, with a set costing $400 to $600. The actual cost will depend on the make and model of your vehicle.

Another big expense comes from the hourly rate for the labor. Most repair shops these days charge around $150 per hour to perform any kind of maintenance service on your vehicle. Fortunately, replacing ignition coils takes about 30-40 minutes for a mechanic to do. So you’re looking at roughly $100 to $200 for the labor costs associated with the job, but higher if there is a minimum labor cost.

If you only have one ignition coil to replace then you’ll be paying anywhere from $200 to $300. But if you are having multiple ignition coils replaced then you could be looking at between $500 and $900 just to accommodate the costs of the extra coils and the additional labor time.

See Also: Ignition Switch Replacement Cost

Ignition Coil Testing Tips

Below are some steps to follow to determine which coil has a malfunction:

  1. Start the engine.
  2. Pull out ignition coil 1.
  3. See the engine condition changes: If the engine becomes rough or vibrates, it likely means that ignition coil is good. If the engine condition remains constant and doesn’t change, it means that ignition coil could be bad. Generally, pulling a good coil will cause the engine to run rougher because it has one less cylinder that is making power. 
  4. Repeat this process with the remaining ignition coils until you find the bad one.

Most often, it’s better for you take your car to an auto repair shop and have them perform a diagnostic test on them. This should cost you between $50 and $100 just for the test. If it turns out that you need new ignition coils then your costs are going to be considerably higher.

Generally, if one coil goes bad then the others aren’t far behind. While you can replace just a single ignition coil, it’s usually recommended to replace all at the same time while you’re in there.


5 thoughts on “5 Symptoms of a Bad Ignition Coil (And Replacement Cost)”

  1. I have a 2005 dodge diesel 5.9. My battery cable shorted out when I tried to replace one battery I left the other connected and shorted out the positive cable for about 5 seconds. placed the battery hooked them up , started the truck and made it about 2 blocks, check engine light came on, truck COMPLETELY shut down, couldn’t get my module to even recognize my truck. Blew a 20amp fuse. I replaced the fuse, with ignition off, and the engine started smoking immediately on the passenger side. so i replaced solenoid and made no difference, still smokin. what in the heck did I do? coil? alternator? Please, some advise? obviously I dont know much about these motors. Man I really need some help here, thank you!


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