How To Test An Ignition Coil

How to Test an Ignition Coil: A Comprehensive Guide

A faulty ignition coil can leave you stranded with a car that won't start. Understanding how to test an ignition coil is a valuable skill for any car owner, saving you potential repair shop costs. This guide provides a step-by-step process to diagnose a failing ignition coil, using both visual inspection and multimeter testing. You'll learn to identify common symptoms and pinpoint the problem quickly and efficiently.

Understanding the Ignition Coil's Role

Before jumping into testing, let's briefly review the ignition coil's function. This critical component in your vehicle's ignition system transforms the low voltage from your battery (typically 12 volts) into the high voltage (upwards of 20,000 volts) needed to ignite the air-fuel mixture in your engine's cylinders. A malfunctioning coil prevents the spark plugs from firing, leading to engine misfires or complete failure to start.

Common Symptoms of a Bad Ignition Coil

Several signs indicate a potential problem with your ignition coil. These include:

• Engine Misfires: Rough running, sputtering, or a noticeable decrease in engine performance. This is often accompanied by a check engine light illuminating.
• Difficulty Starting: The engine cranks but fails to start, or starts intermittently.
• Lack of Power: Reduced acceleration and overall sluggish engine response.
• Backfiring: Noises coming from the exhaust or intake manifold.
• Visible Damage: Cracks, burns, or other physical damage to the coil itself.

Tools You'll Need

To properly test your ignition coil, you'll need these essential tools:

• Multimeter: A digital multimeter is essential for measuring resistance and voltage.
• Spark Plug Wrench: To access and remove the spark plugs (if necessary).
• Wire Connectors: For connecting the multimeter to the ignition coil terminals.
• Safety Glasses: Always protect your eyes when working on your vehicle.
• Gloves: To protect your hands from potential dirt and grease.
• Vehicle Service Manual: Highly recommended for specific coil testing procedures for your particular car model.

Visual Inspection: The First Step

Begin by visually inspecting the ignition coil. Look for any obvious signs of damage, such as:

• Cracks in the casing: Cracks can compromise the coil's insulation and cause short circuits.
• Burn marks: Burn marks are a clear indication of overheating and potential failure.
• Loose or corroded connections: Check the connections to the coil for any signs of corrosion or looseness.

If you find any visible damage, it’s highly likely the coil needs replacing.

Testing the Ignition Coil with a Multimeter

If the visual inspection doesn't reveal any obvious issues, it's time to use a multimeter. Remember that the specific testing procedure might vary slightly depending on the coil's design and your vehicle's specifications. Refer to your vehicle's service manual for detailed instructions. However, the general principles remain consistent:

1. Measuring Primary Resistance:

• Turn off the ignition and disconnect the negative terminal of your battery (safety first!).
• Locate the primary terminals on the ignition coil (usually marked with letters like "A" and "B").
• Set your multimeter to the ohms (Ω) setting.
• Connect the multimeter leads to the primary terminals.
• Your multimeter should display a reading. Compare this reading to the specifications provided in your vehicle's repair manual. A reading outside the specified range indicates a faulty coil.

2. Measuring Secondary Resistance:

• Locate the secondary terminals on the ignition coil (often a high-voltage terminal and ground).
• Set your multimeter to a higher ohms (Ω) setting.
• Connect the multimeter leads to the secondary terminals.
• Again, compare the reading to the specifications in your vehicle's service manual. A reading outside the specified range points to a faulty coil.

3. Testing for High Voltage (Advanced & Requires Caution):

This test requires more advanced techniques and safety precautions. It involves using a high-voltage probe and requires a careful understanding of electrical safety. Attempting this step without the proper knowledge and tools can be dangerous. It's best to leave this test to qualified mechanics.

Replacing the Ignition Coil

If your multimeter tests confirm a faulty ignition coil, replacement is necessary. This is a relatively straightforward process for many vehicles; however, always refer to your car's service manual for specific instructions. Remember that safety should always be your top priority when working with your vehicle's electrical system.

By following these steps and using the proper tools, you can effectively test your ignition coil, saving time and money on potential unnecessary repairs. Remember, safety is crucial, and if you're unsure about any step, consult a qualified mechanic.