What an Ignition Coil Looks Like: A Visual Guide

An ignition coil typically looks either like a small metal cylinder with two small terminals and one tall high-voltage “tower,” or like a compact molded-plastic module with a multi-pin connector and one or more rubber boots that plug directly onto spark plugs. In modern cars, you’ll most often see coil-on-plug units—slim “pencil” coils or a long rail—that sit on top of each spark plug; in older vehicles, you may find a single canister-style coil feeding a distributor via a thick central wire. Below is a detailed visual breakdown to help you identify the variations you’re likely to encounter under the hood.

The Basics: Shape, Size, and Materials

At its core, an ignition coil is a transformer encased for heat and vibration protection. Externally, you’ll usually see a rigid plastic or metal body, a molded electrical connector for the low-voltage side, and either a high-voltage tower for a spark plug wire or a rubber boot that slips directly over a spark plug. The internal iron core and windings are hidden, often potted in epoxy or oil-filled in older designs to aid cooling and insulation.

Common Types You’ll See

Ignition coils come in several distinct shapes, each tied to era and engine design. The following list explains the most common types and their telltale visual cues.

• Canister (oil-filled) coil: A metal cylinder (roughly soda-can diameter, but taller) with an insulated top. It has one central high-voltage tower for the coil wire to the distributor and two small terminals marked “+” and “–” (or 15 and 1) for the low-voltage connections.
• E-core/bracket coil: A compact, blocky unit often mounted on a bracket. It may show a laminated iron “E” core profile and has a single high-voltage tower plus a two-pin or two-post primary connection.
• Coil pack (waste-spark): A plastic “brick” with 2–4 high-voltage towers, each connecting to a spark plug wire. Cylinder numbers may be molded near the towers, and a single multi-pin plug provides power and signals.
• Coil-on-plug (COP) pencil coil: A long, narrow “pencil” with a rubber boot on one end and a small 2–4 pin connector on the top. It mounts directly over each spark plug—often hidden beneath a decorative engine cover.
• Coil rail/cassette: A long, bar-like module that covers a whole bank of cylinders with multiple integrated boots, powered by one multi-pin connector.

These forms reflect how the spark is distributed: a single canister or E-core coil feeds many cylinders via a distributor or pack, while COP and cassette designs place a dedicated coil at each plug for stronger, more precise spark control.

How to Spot It in the Engine Bay

Knowing where to look can make identifying an ignition coil much faster. Use these visual and location clues to find it quickly.

• Follow the spark path: On older cars, track the thick central wire from the distributor cap back to a single coil tower. On modern engines, look for identical modules perched on each spark plug under the valve cover or coil rail beneath a plastic engine cover.
• Mounting points: Coils are bolted solidly to the engine (valve cover or cylinder head) or a bracket on the firewall/engine block to manage vibration and heat.
• Connectors and boots: Expect a molded multi-pin connector for the low-voltage side and either one or more rigid towers (for plug wires) or rubber boots that disappear down to the spark plugs.
• Markings: Look for molded cylinder numbers (on packs), polarity symbols (+/–) on canister coils, and part numbers/branding on the housing.

If you see a sturdy, heat-resistant module with a high-voltage connection pathway and a firm mounting point near the plugs, you’ve likely found the ignition coil assembly.

Distinguishing an Ignition Coil from Similar Parts

Several under-hood components can look similar at a glance. These comparisons help avoid mix-ups.

• Distributor vs. coil: The distributor has a round cap with multiple posts for plug wires; the coil is a single module with a tower/boots and a small electrical connector.
• Spark plug wire vs. coil: Wires are flexible, insulated cables; the coil is a rigid housing with a single or multiple towers or integrated boots.
• Fuel injector vs. coil: Injectors are small, metal/plastic units seated in the fuel rail near the intake; coils are larger, sit higher, and lack fuel plumbing.
• Igniter/ignition module vs. coil: Igniters are flat, heat-sinked electronics boxes; coils are bulkier and connect to spark plugs or plug wires.
• Capacitive discharge box (motorsports) vs. coil: CDI boxes are rectangular electronics modules with multiple connectors; the coil still has a high-voltage tower or boots.

Focusing on the presence of a high-voltage output (tower or plug boot) and its proximity to spark plugs usually differentiates the ignition coil from lookalikes.

Typical Connectors and Terminals

The coil’s wiring points are a strong visual clue. Here’s what the connections generally look like.

• Primary (low-voltage) side: Either two small posts labeled + and – (older coils) or a molded 2–4 pin connector (modern COP/pack) carrying battery power, ground, and a control signal from the ECU.
• Secondary (high-voltage) side: A central tower for a plug wire (single/E-core/pack) or a rubber boot that slips onto the spark plug (COP/rail).
• Additional pins (some systems): Diagnostics or feedback lines may be present on advanced designs.

If you see a two-wire or multi-pin connector plus either a tower or a plug boot, you’re looking at the coil’s electrical interfaces.

Dimensions and Colors You Might Encounter

While sizes vary by vehicle, general ranges and finishes are common. These notes set expectations when scanning the engine bay or parts catalog.

• Canister coils: About 4–6 inches (10–15 cm) tall and 2–3 inches (5–7.5 cm) in diameter, typically black, silver, or painted metal with a plastic top insulator.
• COP pencil coils: Roughly 3–7 inches (8–18 cm) long and 0.8–1.5 inches (2–4 cm) wide, with a black/gray plastic body and black rubber boot. Some performance versions are colored (e.g., red or blue).
• Coil packs/rails: Brick-like modules several inches wide/long; usually matte-black plastic with molded towers/boots.

Color alone won’t identify a coil, but size and the presence of towers or boots are strong indicators.

Safety and Handling Notes

Because coils generate very high voltage, treat them with care during inspection or replacement.

• Never touch coil towers, boots, or plug wires with the engine running—shock hazard.
• Allow the engine to cool before handling coils; they sit in hot zones.
• Disconnect the battery or ignition source before unplugging connectors.
• Pull on the boot, not the wire, when removing spark plug leads to avoid damage.

Basic precautions prevent injury and protect delicate connectors and insulation from accidental damage.

Quick Visual Checklist

Use this rapid checklist to confirm you’ve found the ignition coil.

1. Rigid metal or plastic module, firmly bolted in place.
2. One or more high-voltage outputs: a tower for a wire or a rubber boot onto a spark plug.
3. A small two- to four-pin electrical connector (or +/– posts on older coils).
4. Located near spark plugs, plug wires, or atop the valve cover/cylinder head.
5. Often labeled with polarity, cylinder numbers, or a part number.

If an under-hood component checks all these boxes, it is almost certainly an ignition coil.

Summary

An ignition coil is either a cylindrical canister with a central high-voltage tower and two small terminals, a blocky coil with a single tower, a multi-tower coil pack, or a slim coil-on-plug “pencil” (or long rail) with rubber boots that sit directly on spark plugs. Look for a solidly mounted module featuring a molded low-voltage connector and a clear high-voltage pathway to the spark plugs—those visual traits define the ignition coil across most gasoline engines.

How much does it cost to fix a coil in a car?

Replacing a car’s ignition coil can cost anywhere from $130 to over $600, with the total depending on your vehicle’s make and model, the type of ignition system, and whether you opt for DIY or professional service. Parts can range from $35 to over $300 per coil, while labor costs vary based on the complexity of the job and the hourly shop rate. For example, a common domestic vehicle might be on the lower end, while a complex Japanese import could be significantly more. 
Factors influencing the cost

• Vehicle Make and Model: Costs vary significantly between domestic and imported vehicles, with Japanese models often being more expensive. 
• Type of Ignition System:
  • Conventional coils: are generally less expensive. 
  • Coil-on-plug: and distributorless ignition system (DIS) coils are often more costly, with some models reaching $300-$600 or more per coil. 
• Part Quality: OEM (Original Equipment Manufacturer) coils are often more expensive than aftermarket options. 
• Complexity of Replacement: Some coils are easily accessible on the top of the engine, while others may be located near the firewall, requiring removal of other engine parts, which increases labor time and cost. 
• Labor Costs: Hourly shop rates can differ, and the time it takes to perform the job is a major component of the total cost. 

Typical Cost Breakdown

• Parts: A single ignition coil can cost anywhere from $35 to over $300, depending on the vehicle and system. 
• Labor: A mechanic’s labor for replacing a coil can range from $80 to $150 per hour or more. 

How to Get an Accurate Estimate

1. Identify your vehicle’s make, model, and year: This information is crucial for determining part availability and cost. 
2. Find the faulty coil: A proper diagnosis is needed to identify the specific coil that needs replacing. 
3. Use online estimators: Websites like RepairPal provide estimates based on your vehicle’s information. 
4. Contact local shops: Get quotes from local auto repair shops or dealerships for an accurate estimate of both parts and labor. 

How can you tell if an ignition coil is bad?

You can tell an ignition coil is bad by observing several symptoms, including a flashing Check Engine Light, engine misfires or rough idling, difficulty starting the engine, poor fuel economy, engine stalling, and the occasional backfiring sound. You can also perform diagnostic tests, such as disconnecting coils one by one to see if the engine stumbles, or using an OBD-II scanner to identify misfiring cylinders and swapping suspect coils to a different cylinder to see if the misfire follows the coil. 
Symptoms of a Bad Ignition Coil

• Check Engine Light: A flashing or solid Check Engine Light will often illuminate when the car’s computer detects a problem with the ignition system, such as an engine misfire. 
• Engine Misfires and Rough Idling: A bad coil can cause a cylinder to not ignite fuel properly, leading to an uneven engine operation, shaking, or jerking. 
• Difficulty Starting: A weak or faulty coil might not deliver enough voltage to the spark plug, making the engine harder to start or causing it to crank for a long time before starting. 
• Reduced Power and Poor Fuel Economy: Insufficient voltage from the coil leads to incomplete combustion, which reduces engine performance and causes the engine to work harder, consuming more fuel. 
• Engine Stalling: A coil that fails intermittently can cause the engine to suddenly die while idling or driving. 
• Backfiring: Unburned fuel that exits the engine and enters the exhaust can ignite, creating a loud popping sound known as backfiring. 
• Unusual Smells: A strong smell of gasoline from the exhaust can also be a sign of unburned fuel due to a misfiring cylinder from a bad coil. 

Diagnostic Steps

1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to retrieve codes that point to a specific cylinder misfire. 
2. Disconnect and Listen: With the engine running, disconnect the electrical connector to each ignition coil one at a time. A good coil will cause the engine to run worse when its connection is removed; a coil that does not change the engine’s behavior is likely the faulty one. 
3. Swap and Test: If you identify a misfiring cylinder with a scanner, you can swap the ignition coil from that cylinder to another. If the misfire moves to the new cylinder, you have confirmed a bad coil. 
4. Visual Inspection: Inspect the ignition coil for any visible damage, such as cracks in the casing or signs of burning, as these can lead to misfires. 

Where are ignition coils located?

Ignition coils can be located in a few different places, depending on the vehicle’s age and ignition system: they may be in the engine bay, mounted directly on the spark plugs in coil-on-plug (COP) systems, in a coil pack, or inside the distributor on older cars. To find the specific location for your car, you may need to remove a plastic engine cover and consult your owner’s or repair manual, according to Advance Auto Parts and CarParts.com. 
Older Vehicles (with Distributor)

• In older cars with a traditional ignition system, a single coil is often located in the engine bay and connects to the distributor. 
• On some older GM vehicles, the coil may be mounted directly on top of the distributor cap, like an HEI coil. 

This video demonstrates how to remove an ignition coil from an older vehicle: 53sebayYouTube · Jun 24, 2024
Modern Vehicles

• Most modern cars use a coil-on-plug (COP) system, where one ignition coil is placed directly over each spark plug. 
• You can typically find these by removing any plastic engine covers on top of the engine. 
• You may also find what’s called a wasted spark system, which uses coil packs mounted to the engine to fire pairs of spark plugs. 

This video shows how to replace a coil-on-plug system in a modern vehicle: 1mFCP EuroYouTube · Sep 11, 2022
How to Find the Coil in Your Car

1. Open the Hood: With the engine off, open the hood to access the engine bay. 
2. Remove Engine Covers: Look for any plastic covers or components of the air intake system that may be in the way and carefully remove them. 
3. Identify the Coils: Look for the individual coils mounted on the engine, usually over the spark plugs. 
4. Check Your Manual: If you’re still unsure, consult your vehicle’s owner’s manual or a repair manual for the exact location of the ignition coils. 

How do ignition coils work with spark plugs?

An ignition coil works with a spark plug by converting the vehicle’s low-voltage electrical current into the tens of thousands of volts necessary to create a spark at the spark plug’s tip. This process, known as electromagnetic induction, involves a magnetic field that collapses within the coil, inducing a high-voltage current. This high-voltage current is then sent to the spark plug, which ignites the air-fuel mixture in the engine’s cylinder at the precise moment required for combustion.
 
This video explains how an ignition coil works step-by-step: 56sspeedkar99YouTube · Dec 25, 2017
How the process unfolds:

1. Low-voltage current: Opens in new tabThe vehicle’s battery provides a low-voltage electrical current to the ignition coil. 
2. Magnetic field creation: Opens in new tabThis current flows through a primary winding of wire around a central core within the ignition coil, creating a magnetic field. 
3. Magnetic field collapse: Opens in new tabA switching circuit, controlled by the engine’s computer (or distributor on older vehicles), interrupts the primary current. 
4. Electromagnetic induction: Opens in new tabAs the magnetic field collapses, it induces a high-voltage current in a secondary winding of the coil, which contains many more turns of wire than the primary. 
5. Spark plug ignition: Opens in new tabThis high-voltage current travels to the spark plug. The voltage then jumps across a small air gap at the tip of the spark plug, creating a hot spark. 
6. Combustion: Opens in new tabThe spark ignites the air-fuel mixture within the engine cylinder, producing the power needed to drive the engine’s pistons. 

Key components and roles:

• Ignition Coil: Opens in new tabActs as a step-up transformer, using electromagnetic induction to boost the voltage. 
• Spark Plug: Opens in new tabA device at the end of the ignition system that receives the high voltage from the coil to create the spark. 
• Air-fuel mixture: Opens in new tabThe combustible combination of fuel and air in the engine’s cylinders that the spark ignites. 

In modern vehicles, a “coil-on-plug” design is common, where each spark plug has its own dedicated ignition coil for more precise and efficient ignition.