6 Symptoms Of A Bad Ignition Coil (& Replacement Cost)

The ignition coils are known to fail due to the heat they are exposed to. Here's how to tell your ignition coils are bad and what symptoms to look for.

Symptoms Of A Bad Ignition Coil

An ignition coil is a transformer that is used to convert and supply enough current to the spark plug to produce a spark and start the engine. It is a key component of the car’s ignition system, and if it is faulty, your car will not start.

Therefore, if this part fails, you may have serious problems with your car engine.

In this article, we will look at the symptoms of a bad ignition coil and examine what preventive measures could be taken to ensure the ignition coil’s long life. What are the symptoms of a bad ignition coil?

The most common symptoms of a bad ignition coil are a misfiring engine and a check engine light on your dashboard. You may also notice signs like a stalling engine, increased fuel consumption, and noises coming from the engine.

Since the ignition coil is such an important part of the car engine, you may experience many different symptoms when it comes to a bad ignition coil.

Here is a more detailed list of the signs of a bad or failing ignition coil to look for:

Symptoms Of A Bad Ignition Coil

1. Check Engine Light

Check Engine Light

The check engine light illuminates if there is a problem with the engine. As the ignition coil has a direct effect on the engine’s functioning, the check engine light starts to flash if there is a problem with the coil.

If you have noticed any of the symptoms below and the check engine light, the problem is most likely with the ignition coil.

2. Engine Backfires & Misfires

Backfire E1609774966542

Engine backfiring is noticed in the early stages of an ignition coil failure. Backfiring occurs when there is an unburned fuel in the combustion cylinder, and it flows through the exhaust pipe.

This also causes black smoke to escape from the exhaust pipe and a bad smell of gasoline, indicating that there may be a problem with the ignition coil. It is recommended that this problem be corrected immediately to avoid damage to the exhaust system.

3. Engine Stalling

Engine Stall E1609780473516

If you have a single ignition coil, firing up a distributor – Common in old cars, your car might stall while driving. If you are driving at normal speed and after a few kilometers, you notice that your engine stops, there is a possibility that the ignition coil is defective. An engine stall occurs when the ignition coil delivers irregular current to the spark plug. If it is not repaired immediately, your car may come to a complete stop after a few miles.

If you have a newer car with separate ignition coils, your car will most probably not stall while driving if just one ignition coil has gone bad.

4. Poor Fuel Economy

Car High Cost E1609780565655

Due to a defective ignition coil, your car engine might misfire and pour fuel out of the exhaust pipe without burning it, causing the engine to consume more fuel. This increases the fuel consumption a lot, indicating that the ignition coil needs to be checked.

5. Strange Engine Noise

Car Engine Noise 1 E1609780485672

A defective ignition coil does not generate enough voltage for the spark plug, so the engine works harder than usual.

If your engine is running on one cylinder less than usual because of a bad ignition coil, your car might sound like a tractor and make strange engine noise.

6. Car Does Not Start at All

Hard Starting

A damaged or faulty ignition coil can prevent the engine from starting completely. If you hear a clicking sound when starting the car, the problem is not with the ignition coil.

However, if there is absolutely no sound, there is a possibility that the ignition system has failed, especially if you have an older car with a single ignition coil for all cylinders.


The Function of the Ignition Coils

Ignition Coil

The car’s ignition system aims to generate a high voltage from the car battery and transfer this voltage to the spark plugs. With this 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 takes voltage from the car’s 12-volt battery and converts it to 25-30,000 volts, which are needed by the spark plug for ignition.

Ignition Coil Location

Ignition Coil Location E1609826510799

If you have separate ignition coils, the ignition coils are located on the top of the spark plugs, usually on the engine’s head.

But if you have one separate ignition coil and a distributor, it is often installed at the car’s body, near the distributor.

Ignition Coil Replacement Cost

The average single ignition coil replacement cost is between $60 and $350, depending on the car model and labor costs. The cost of a single ignition coil is between $30 and $150. The labor cost of an ignition coil is between $30 and $200.

The replacement of an ignition coil is often pretty straightforward, and you can easily replace it yourself, but in some car models, the job can take an hour or two; that’s why you should expect a quite high replacement cost in some cases.

Changing the ignition coil is often easy, but if you don’t feel comfortable doing it yourself, go to the car mechanic and let the experts do the work.

Conclusion: Bad Ignition Coil Symptoms

The main symptoms of a bad ignition coil include:

  • Check engine light
  • Engine backfires and misfires
  • Stalling engine
  • Poor fuel economy
  • Strange engine noise
  • Car Does Not Start at All
Magnus Sellén
Written by:

Magnus is the owner and main author of Mechanicbase. He has been working as a car mechanic for over 10 years, and the majority of them specialized in advanced car diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.

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