Ignition Coil change & replacement made easy

How does an ignition coil work?

The ignition coil is the part of your car’s ignition system that makes sure your engine starts and runs smoothly. Essentially, it acts like a transformer, taking the low-voltage power from your battery (usually 12 volts) and boosting it to a high voltage, often exceeding 50,000 volts. This high voltage is necessary to create a strong spark at the spark plugs, which ignites the fuel-air mixture inside the engine’s cylinders.
By efficiently converting and boosting the battery’s power, the ignition coil ensures that each cylinder fires correctly. Without a properly functioning ignition coil, your engine might misfire, struggle to start, or even stall, leading to poor performance and reduced fuel efficiency.
Keeping your ignition coil in top condition is essential for reliable engine operation. If you experience starting difficulties or notice a misfiring engine, it’s a good idea to have your ignition system checked by a qualified mechanic to determine if the ignition coil needs replacing.

What does an ignition coil replacement job involve?

When your vehicle's ignition coil needs replacing, a professional mechanic generally follows a similar step-by-step process to ensure your ignition system is restored to optimal working order:

• The mechanic begins by reading the car’s ECU to identify any fault codes related to the ignition system. This diagnostic step helps pinpoint whether the ignition coils are at fault.

• Next, the mechanic thoroughly inspects the entire ignition system along with the spark plugs. This inspection confirms the condition of the coils and ensures that no other related issues are present.

• If the ignition coils are determined to be faulty, the mechanic carefully removes the old coil pack(s) and installs new, manufacturer-approved components to restore reliable engine firing.

• During the process, the mechanic may also evaluate other parts of the ignition system.

• Finally, the mechanic starts the engine and takes the vehicle for a test drive to verify that the ignition system is functioning correctly and the engine runs smoothly. Any necessary adjustments are made to ensure optimal performance.

How do I know when I need an ignition coil replacement?

If your vehicle's ignition coil is beginning to fail, you may notice these common signs that indicate it might be time to replace it:

• Difficulty starting the car: The coil may not be providing enough voltage to ignite the fuel-air mixture.
• Engine misfires: You might feel the engine shake or hesitate, especially under acceleration.
• Reduced power or poor fuel economy: Weak sparks cause inefficient combustion, lowering performance and miles per gallon.
• Sluggish acceleration: The car may struggle to pick up speed smoothly.
• Sputtering or rough start-up: The engine may sound uneven when you first turn the key.
• Unusual vibrations: A rough idle or shaking may occur due to one or more cylinders not firing properly.
• Check Engine Light: A diagnostic scan may reveal ignition-related fault codes.

If you notice any of these symptoms, it’s important to have your ignition system inspected by a qualified mechanic to prevent further issues and ensure your car runs smoothly and efficiently.

Can the ignition coil be repaired?

In most cases, an ignition coil cannot be repaired. These components are sealed units, so once they start to fail, internal damage or insulation breakdown can’t be easily fixed. While cleaning the coil or its connections might give a temporary improvement, it won’t restore full performance.

For long-term reliability, ignition coil replacement is the best option. Replacing a faulty coil ensures your engine receives a strong, consistent spark, vital for smooth acceleration, fuel efficiency, and proper combustion.

If you’re noticing ignition coil failure symptoms such as misfires, difficulty starting, or loss of power, it’s best to have your ignition system inspected by a qualified mechanic. They can confirm whether a new ignition coil is needed to keep your car running smoothly.

Can I drive with a bad ignition coil?

Technically, you can drive with a bad ignition coil, but we’d not recommend it. A faulty ignition coil can cause engine misfires, rough idling, and a noticeable loss of power. Continuing to drive in this condition can damage your catalytic converter, reduce fuel efficiency, and increase emissions.

In some cases, the engine may stall or fail to start altogether, leaving you stranded. That’s why it’s best to address the issue as soon as possible.

If you’re experiencing symptoms like difficulty starting, uneven acceleration, or a rough-running engine, have your vehicle inspected by a qualified mechanic. Replacing a failing ignition coil ensures proper combustion, restores performance, and keeps your car safe to drive.

Can I replace the ignition coil myself?

If you’re comfortable with car maintenance and have the right tools and technical repair skills, you could replace an ignition coil yourself. However, coils sit atop the spark plugs and connect to sensitive electrical wiring, so you’ll need to proceed carefully. We recommend it’s best that a qualified technician replaces an ignition coil to ensure it is done to a good standard.

How to test an ignition coil?

Here’s a simple overview of how a mechanic, or perhaps a confident DIYer, might test each coil safely.

Safety first: Ignition systems generate high voltage. If you’re not familiar with using a multimeter or working near live electrical parts, it’s safest to have a qualified mechanic carry out these checks.
Visual inspection: Examine the coil housing and connector for cracks, burn marks, melted plastic, or corrosion. These are clear signs the coil may be failing.
Primary resistance test: Using a multimeter set to ohms, measure across the small electrical terminals. A healthy reading is usually between 0.4 Ω and 2 Ω. Readings outside this range suggest internal damage.
Secondary resistance test: On the high-ohm scale, measure between one small terminal and the high-voltage output (spark-plug connection). Expect around 5 kΩ – 15 kΩ; a much higher or lower value points to a faulty coil.
Spark output test: Reconnect the coil, attach an inline spark tester, and crank the engine. A strong, steady blue spark means the coil is working; a weak or irregular spark means it isn’t.

Even if these steps seem straightforward, testing ignition coils incorrectly can cause damage or injury. The safest and most reliable option is to have your ignition system professionally tested and any faulty ignition coils replaced to keep your engine running smoothly.

How much does an ignition coil replacement cost?

An ignition coil replacement typically ranges from £70 to £220, with an average cost of £150 per coil. If your vehicle needs multiple coils replaced, the total price will increase based on the number of parts and the additional labour time required. Labour rates also vary by location—mechanics in London usually charge around £50–£100 per hour, whereas in smaller towns you can expect rates closer to £35–£50.

Use our free price estimator tool to find out what you could save by having your ignition coil repaired by ClickMechanic!

What does a ClickMechanic ignition coil replacement quote cover?

Unless otherwise stated, the quote will cover:

• The cost of the ignition coil
• Coming to you
• Fitting of the parts
• Disposal of the old parts (unless you request to keep them)
• VAT (if applicable)
• 12-month parts and labour warranty

Can a mobile mechanic replace the ignition coil?

Yes, a mobile mechanic can replace your ignition coil at your home or workplace. Most vehicles use accessible coil-on-plug systems, which mobile mechanics can safely replace using on-board diagnostic tools and manufacturer-approved parts.
In some cases, where the ignition coils are buried under other engine components or require specialist workshop tools, the mobile mechanic will diagnose the fault and recommend a garage repair instead.
With ClickMechanic, if your vehicle needs further attention, free collection and delivery are available to make the process as easy and convenient as possible.