Defective ignition coil: Symptoms, causes & repair costs

Defective ignition coil – what does it mean?

The ignition coil is an essential component in the engine that is responsible for generating the ignition voltage. Without a functioning ignition coil, the engine cannot start or runs unevenly. But how do you know if the ignition coil is faulty? What are the causes and what does the repair cost?

In this blog, you can find out everything about the symptoms of a defective ignition coil, possible causes and how you can rectify the fault.

How does an ignition coil work?

The ignition coil converts the low voltage of the car battery (12V) into a high ignition voltage of up to 40,000 volts. This high voltage is necessary to generate the ignition spark at the spark plug and thus ignite the fuel-air mixture in the engine.

There are different designs depending on the vehicle model:

• Single ignition coils – One ignition coil per cylinder
• Dual ignition coils – One coil supplies two cylinders
• Ignition coil bank – One unit for all cylinders

If the ignition coil fails, the engine can no longer work properly, resulting in a loss of power and increased fuel consumption.

Symptoms of a defective ignition coil

A defective ignition coil can be recognized by various warning signals. Here are the most common symptoms:

1. Engine jerks or runs rough

A defective ignition coil causes misfiring. The engine runs irregularly and jerks, especially when accelerating or idling.

2. Loss of power & increased fuel consumption

As one or more spark plugs no longer fire properly, the engine no longer runs optimally. As a result, performance decreases while fuel consumption increases.

3. Starting problems or engine stalls

If the ignition coil fails completely, the engine can only start with difficulty or not at all. In some cases, the vehicle stalls while driving.

4. Indicator light comes on

A defective ignition coil often causes the check engine light (MKL) to illuminate. An OBD diagnosis can provide clarity here.

5. Unpleasant smell of petrol coming from the exhaust

Incomplete combustion can cause fuel to enter the exhaust, resulting in an intense smell of petrol.

Causes of a defective ignition coil

An ignition coil can be damaged by various factors. The most common causes are:

1. Age-related wear and tear

Ignition coils are constantly exposed to high temperatures and stresses. Over time, they can wear out and fail.

2. Overheating & short circuits

High temperatures or faulty wiring can lead to short circuits in the ignition coil.

3. Defective spark plugs

Worn or incorrectly adjusted spark plugs put a strain on the ignition coil as it has to supply more energy.

4. Moisture & corrosion

Water or oil in the engine compartment can penetrate the ignition coil and cause damage.

5. Incorrect spare parts or inferior quality

Cheap ignition coils or ignition coils that do not fit the vehicle can fail quickly.

How is a defective ignition coil diagnosed?

If you notice symptoms of a defective ignition coil, you can have a diagnosis carried out in the workshop.

Diagnostic options:

• Read out the fault memory: An OBD scanner can be used to detect fault codes such as P0300 – P0312 (misfiring).
• Visual inspection: Cracks, traces of melting or moisture on the ignition coil indicate defects.
• Measure resistance: A multimeter can be used to check whether the ignition coil is still working.

If the ignition coil is defective, it should be replaced promptly to prevent engine damage.

How much does an ignition coil repair cost?

The cost of replacing an ignition coil depends on the type of vehicle, the number of coils affected and the workshop.

Repair	Costs (approx.)
New ignition coil (single coil)	30 – 150 €
New ignition coil strip	100 – 400 €
Installation in the workshop	50 – 150 €
Total costs (single coil)	80 – 300 €
Total costs (several coils)	250 – 800 €

When is a repair no longer worthwhile?

If your vehicle already has a lot of kilometers on the clock or additional repairs are due, it may make more economic sense to sell the car instead of paying high costs for replacing the ignition coils and other components.

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Conclusion: Recognize a defective ignition coil in time & take action

A defective ignition coil can significantly impair engine running and should be replaced as soon as possible. The most common symptoms are juddering, loss of power and an illuminated check engine light.

The repair costs are between 80 and 800 euros, depending on the number of ignition coils required. If further damage or high costs are foreseeable, a sale may be the better solution.

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