will a bad ignition coil cause car not to start

by:Haiyan     2023-07-10

Will a Bad Ignition Coil Cause a Car Not to Start?


The ignition coil is a vital component of a car's ignition system, responsible for transforming the battery's 12-volt power into the high voltage needed to create a spark in the spark plugs. If the ignition coil malfunctions, it can have a significant impact on the engine's performance, potentially causing the car not to start. In this article, we will explore the role of the ignition coil, signs of a faulty ignition coil, potential causes of failure, and steps to diagnose and replace a bad ignition coil.

Understanding the Ignition Coil

1. The Purpose of the Ignition Coil

The ignition coil's primary function is to produce a high voltage electrical charge, which is essential for igniting the air-fuel mixture in the combustion chamber. This process starts the engine and keeps it running smoothly. It achieves this by increasing the 12-volt battery voltage to several thousand volts that can jump the spark plug gap.

2. Signs of a Faulty Ignition Coil

A bad ignition coil can manifest through various symptoms, including:

a. Difficulty or Inability to Start

One of the most common signs of a faulty ignition coil is the inability to start the car. When the coil fails, it won't generate enough voltage to create a spark, causing the engine to crank without igniting.

b. Rough Idling or Stalling

A malfunctioning ignition coil can result in a rough idle or cause the engine to stall intermittently. Since the coil is responsible for providing the spark that ignites the air-fuel mixture, a weak or inconsistent spark can disrupt the smooth operation of the engine.

c. Decreased Fuel Efficiency

If the ignition coil isn't generating enough voltage to create a proper spark, it can lead to incomplete combustion. This inefficiency translates to increased fuel consumption and reduced mileage. If you notice a sudden drop in fuel efficiency, a faulty ignition coil could be the culprit.

d. Engine Misfires

A malfunctioning ignition coil can cause engine misfires, resulting in a loss of power and poor overall performance. Engine misfires occur when the spark plug doesn't receive the necessary electrical charge, leading to incomplete combustion in one or more cylinders.

e. Illuminated Check Engine Light

A failing ignition coil can trigger the check engine light. Modern cars are equipped with onboard diagnostic systems that detect faults in various components, including the ignition coil. If the system detects a problem, it illuminates the check engine light on the dashboard.

Diagnosis and Replacement

3. Diagnosing a Bad Ignition Coil

To diagnose a bad ignition coil, you can perform the following steps:

a. Check for Trouble Codes

Connect an OBD-II scanner to retrieve any diagnostic trouble codes related to the ignition system. These codes can provide insights into the specific problem.

b. Inspect the Ignition Coil

Physically inspect the ignition coil for signs of damage, such as cracks, corrosion, or oil residue. Ensure all the connections are secure and free from debris.

c. Perform a Spark Test

Use a spark tester to check for a strong, consistent spark. If the spark appears weak or is absent, it indicates a faulty ignition coil.

4. Replacing the Ignition Coil

If you've determined that the ignition coil is faulty, follow these steps to replace it:

a. Locate the Ignition Coil

Consult your vehicle's repair manual to identify the ignition coil's location. In most cars, the coil is either mounted on the engine or near the spark plugs.

b. Disconnect the Battery

Before starting any work, disconnect the negative terminal of the battery to ensure safety.

c. Remove the Old Ignition Coil

Disconnect the electrical connectors and ignition wires from the faulty coil. Remove any mounting bolts or screws securing the coil in place.

d. Install the New Ignition Coil

Position the new ignition coil in place and secure it with the mounting hardware. Reconnect the electrical connectors and ignition wires.

e. Reconnect the Battery

Once the new coil is installed, reconnect the negative terminal of the battery.


A bad ignition coil can be a frustrating problem, often resulting in a car that refuses to start. Understanding the signs of a faulty ignition coil and learning how to diagnose and replace it can save time and money. By promptly addressing a malfunctioning ignition coil, you can ensure a reliable and efficient vehicle performance. Remember, if in doubt, consult a professional mechanic for assistance in diagnosing and resolving any ignition coil issues.

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