ignition coil symptoms

Symptoms of a Bad Ignition Coil & Replacement Cost

In Engine by Magnus Sellén2 Comments

ignition coil symptoms

With a bad ignition coil – Your car engine may suffer from sudden stalling or hard starting conditions.

An ignition coil is a transformer which is used to convert and provide the spark plug with enough electricity so that it creates a spark and starts the engine. It is a key component of the car’s ignition system and if found faulty, your car will not start.

Any problem with the ignition coil wouldn’t allow the car to start making drivers believe that there is some serious problem with the engine, whereas its just the ignition coil which needs to be replaced. In this article, we will look at the symptoms of the bad ignition coil and what preventive steps one could take a long life of the ignition coil.

The Function of the Ignition Coil

The purpose of the car’s ignition system is to produce a high voltage from the car’s battery and transfer this voltage to the spark plugs. Using the voltage, the spark plug will ignite the fuel-air mixture and start the engine.

The ignition coil is basically a high voltage, a low current transformer that extracts voltage from the car’s 12-volt battery and converts it into 25-30,000 volts which are needed by the spark plug to ignite.

Signs of a bad ignition coil

The most common problems with a bad ignition coil are misfires. Misfires can result in further damages to other parts like the catalytic converter or the O2 sensors. Misfires are absolutely a thing to fix as soon as possible, to not damage other parts.

Moderns engines have multiple spark plugs on each cylinder and each spark plug has a dedicated ignition coil. Each ignition coil is either connected directly or through wires. There are some common problems which are faced if the ignition coil is faulty and we will look at some of them here:

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1. Check Engine Light

The check engine light illuminates whenever there is some problem with the engine. Since the ignition coil directly affects the engine’s functionality, the check engine light starts blinking if there is a problem with the coil. If you have noticed any of the below-mentioned symptoms along with check engine light, then most likely the issue is with the ignition coil.

2. Engine Backfires

Engine backfiring is noticed at early stages of ignition coil failure. The backfiring occurs when the internal combustion cylinder has unused fuel remaining and it flows through the exhaust pipe. This also results in black smoke coming out the exhaust pipe and bad smell of gasoline indicating that there could be a problem with the ignition coil. It is recommended to fix this problem right away to avoid damage to the exhaust system.

3. Engine Stalling

Driving at a regular speed, if you notice that your engine stalls after a couple of miles, then there is a possibility that the ignition coil is faulty. Engine stalling occurs when the ignition coil supplies irregular current to the spark plug. If not fixed right away, your car might completely stop after a few miles.

4. Poor Fuel Economy

Due to a faulty ignition coil, more power is supplied to the spark plug and as a result, the engine will use more fuel. This causes a drop in the mileage indicating that the ignition coil needs to be checked.

5. Loud Engine Noise

A faulty ignition coil does not generate enough voltage for the spark plug as a result, the engine works harder than usual. This results in excessive engine noise and vibration.

6. Car Does Not Start at All

A damaged or faulty ignition coil can prevent the engine from turning on completely. If you hear a clicking sound when starting the car, then the problem is not with the ignition coil. However, if there is absolutely no sound, the possibility is that the ignition system has failed.

ignition coil

Single Cylinder Ignition Coil

Testing an Ignition Coil

An ignition coil can be easily tested using a digital 10 megaohm impedance ohmmeter if you are a bit familiar with car electronics.

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 Connect the ohmmeter’s two test leads to the ignition coil’s positive and negative terminals. The average reading is somewhat between 0.4 and 2 ohms. If the ohmmeter shows zero resistance, it means that the coil is short. Whereas, a high resistance reading indicates an open coil.

Another great way to check the ignition coil is by using a spark tester. A spark tester is available on Amazon for a cheap price. To check the ignition coil, turn off the engine and disconnect the coil from the spark plug. Connect one end of the spark tester to the top of the spark plug and another end to the coil output.

Once the spark tester is in its place, start the engine to check if a light flashes on the spark tester. If it does, then the ignition coil is working effectively, whereas no light indicates that either the ignition coil or the oil control circuit is damaged.

If you are interested in getting one at home you can check our it here on Amazon:
Spark Plug Engine Ignition Tester

ignition coil long

Ignition Coil Pack

Replacing the Ignition Coil

Once you are sure that the ignition coil is faulty, it is time to replace it. The replacement procedure could be done at home provided you have the right tools. Follow these steps to properly replace the ignition coil:

Step 1: Disconnect the car battery by removing the negative terminal. You’ll need an appropriate socket or wrench to unscrew the bolt.

Step 2: Find the ignition coils which are typically located on top of the engine and attached to the engine block.

Step 3: Remove the old ignition coil with the help of a socket wrench and disconnect the electrical connectors from the coil as well. On some cars, it is required to disconnect the electrical connectors first and then removing the coil. To know more, refer to the instructions on your car manual.

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Step 4: Install the new ignition coil and ensure all bolts and screws are tight enough. If you removed the electrical connectors first, then reconnect them and then install the ignition coil.

Step 5: Re-connect the battery’s negative terminal

Step 6: Start the car and take it out for a spin to ensure that there is no idling, stalling or engine misfire.

Ignition Coil Replacement Cost

Replacing the ignition coil is simple, however, if you are not comfortable in doing it yourself, head over to the auto mechanic and let the experts do the job. The average cost to replace the ignition coil is between $150 to $270. The ignition coil itself costs approximately $120 to $160.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

  1. I have a 2010 Hyundai Elantra with only 71,ooo kms. It started running rough 2 years ago. No check engine light. I cleaned the MAF sensor, throttle body sensor, IAC idle motor and replaced the plugs that seemed ok except a little black. I had the engine motor vacted , exhaust tale pipe has no carbon. Still have a rough idle. When the outside temperature is colder and I out the engine under load it is worse. It does improve after the engine warms up, but still not smooth like it was. Sometimes it seems like it is missing going up hill . It drives ok except sometimes. I still have no solution. I had a autel scanner that showed the short term fuel trim was taking some fuel away because eof a rich condition but the long term fuel trim is close to 0. Both fuel trims together look good. All other live data from the scanner look normal.. I am still lost finding this problem . It use to idle so smooth you can not feel it while idling. Now you can feel it in the steering wheel and car body. Can you help! Thanks Ed

  2. I just had my coils replaced in my Ba Ford it was driving really well now seems to be smoke coming out of the exhaust is this normal

  3. Due to a very high demand and high ammount of comments, you have to wait for some time for your car questions to get answered. If you want to get fast answers from a certified master technician you can ask your questions here:
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