How Do I Test An Ignition Coil

How Do I Test an Ignition Coil? A Comprehensive Guide

Meta Description: Learn how to test your ignition coil effectively using both visual inspection and multimeter tests. This guide provides step-by-step instructions for diagnosing a faulty ignition coil and avoiding costly misdiagnoses.

A malfunctioning ignition coil can leave you stranded with a non-starting vehicle. Before replacing it and spending potentially unnecessary money, though, it's crucial to know how to properly test your ignition coil. This guide walks you through the process, from visual inspection to multimeter testing, ensuring you can accurately diagnose the problem.

Visual Inspection: The First Step

Before breaking out the multimeter, start with a simple visual inspection. This quick check can often identify obvious problems and save you time. Look for:

• Physical Damage: Check the coil for any cracks, burns, or signs of physical damage to the casing or wires. Even minor damage can compromise its functionality.
• Loose Connections: Inspect the wiring harness connected to the coil. Look for any loose, corroded, or damaged connectors. Secure any loose connections.
• Corrosion: Examine the coil for signs of corrosion, particularly around the terminals. Corrosion can impede electrical conductivity.
• Fluid Leaks: Check for any signs of oil or coolant leaks near the coil. These leaks can indicate a more serious underlying problem.

If you notice any of these issues, it's highly likely the coil needs replacement. However, even if the visual inspection reveals nothing obvious, further testing is needed to confirm its functionality.

Testing with a Multimeter: The Definitive Check

A multimeter is the essential tool for accurately testing an ignition coil's functionality. Here's how to conduct the tests:

1. Safety First: Always disconnect the negative terminal from your car battery before performing any electrical tests. This prevents accidental shocks and damage to your vehicle's electrical system.

2. Primary Resistance Test:

• Set your multimeter: Set the multimeter to the ohms (Ω) setting. A low resistance setting (e.g., 200Ω) is usually appropriate.
• Connect the leads: Connect the multimeter leads to the coil's primary terminals (usually larger). Consult your vehicle's wiring diagram if unsure about terminal identification.
• Read the resistance: The multimeter will display a resistance reading. Compare this reading to the specification provided in your vehicle's repair manual or online resources. A resistance value outside the specified range indicates a faulty coil. A reading of infinity suggests an open circuit.

3. Secondary Resistance Test:

• Set your multimeter: Change the multimeter setting to a higher ohms range (e.g., 20kΩ or higher)
• Connect the leads: Connect the multimeter leads to the coil's secondary terminals (usually smaller). One terminal will be connected to the spark plug wire connector, and the other to the coil body.
• Read the resistance: Again, compare the reading to the manufacturer's specifications. A value outside the range, or infinity, indicates a problem.

4. Testing for Spark (Advanced): This step requires some caution and knowledge.

• Disconnect the spark plug wire: Carefully disconnect the spark plug wire from the coil's secondary terminal.
• Connect a spark plug: Attach the spark plug wire to a spark plug. Ground the spark plug (metal portion) to the engine block.
• Use a helper: Have a helper crank the engine.
• Observe the spark: Look for a strong, consistent spark across the spark plug gap. A weak or absent spark indicates a faulty coil. Caution: Be careful not to touch the spark plug or wiring while the engine is cranking.

Interpreting the Results

If any of the resistance tests show values outside the specified range, or if you observe a weak spark (or no spark) during the spark test, the ignition coil is likely faulty and needs replacement. Remember to always consult your vehicle's service manual for specific resistance values.

Conclusion

Testing an ignition coil doesn't require specialized equipment beyond a multimeter and some basic electrical knowledge. By following these steps and comparing your readings to manufacturer specifications, you can confidently determine if your ignition coil needs replacement, saving you time and money. Remember to always prioritize safety and consult your vehicle's repair manual for specific information related to your make and model.