how to test an ignition coil with an ohmmeter

3 min read 07-02-2025

how to test an ignition coil with an ohmmeter

Meta Description: Learn how to test your ignition coil with an ohmmeter using this comprehensive guide. We'll cover everything from gathering tools and understanding resistance readings to troubleshooting common problems. Get your engine running smoothly again! (158 characters)

A malfunctioning ignition coil can leave your car stranded. Fortunately, testing an ignition coil with an ohmmeter is a relatively straightforward process. This guide will walk you through the steps, helping you diagnose the problem and get back on the road.

Tools You'll Need

Before you begin, gather these essential tools:

Ohmmeter (Multimeter): This is the key tool for measuring the electrical resistance of the coil. Make sure your multimeter is set to the ohms (Ω) function.
Vehicle Service Manual: Consult your vehicle's manual for specific coil resistance specifications. These values vary greatly depending on the vehicle's make, model, and year.
Screwdrivers: You might need Phillips and/or flathead screwdrivers to access the ignition coil.
Safety Glasses: Always protect your eyes when working on your vehicle.
Gloves (Optional): For added protection.

Locating Your Ignition Coil

The ignition coil's location varies depending on the vehicle. Consult your service manual for the exact location. It's often found near the distributor (in older vehicles) or on the engine's valve cover.

Understanding Ignition Coil Resistance

The ignition coil contains primary and secondary windings. Your ohmmeter will measure the resistance (opposition to the flow of current) in these windings. The service manual will provide the acceptable resistance ranges for both. Readings outside these ranges indicate a faulty coil.

Step-by-Step Testing Procedure

1. Disconnect the Ignition Coil: Disconnect the coil's wiring harness and any negative battery cable before starting. This prevents accidental electrical shocks.

2. Set Your Ohmmeter: Select the ohms (Ω) setting on your multimeter. Start with a higher range (like 200Ω) and switch to a lower range if necessary to get a more accurate reading.

3. Test the Primary Winding: Your service manual will specify which terminals to test for the primary winding. Touch the probes of your ohmmeter to the appropriate terminals on the ignition coil. Note the reading. Does it fall within the range specified in your vehicle's manual?

4. Test the Secondary Winding: Repeat step 3, but this time, test the terminals for the secondary winding, as outlined in your service manual. Note the reading. Again, compare it to your vehicle's specifications.

Interpreting the Results

Readings within the specified range: The ignition coil is likely working correctly. However, other components might still be faulty.
Readings outside the specified range: The ignition coil is likely defective and needs to be replaced.
Infinite Resistance (OL): This indicates an open circuit (broken wire or component) and signifies a faulty coil.
Zero Resistance (0 Ω): This means a short circuit (unwanted electrical connection) and indicates a faulty coil.

Common Problems and Troubleshooting

Problem: Ohmmeter reads infinitely high resistance on both primary and secondary windings. Solution: This indicates a complete break in the coil's windings. The coil needs to be replaced.

Problem: Ohmmeter reads zero resistance on the primary or secondary winding. Solution: This indicates a short circuit. The coil needs to be replaced.

Problem: Resistance readings are within the range, but the engine still misfires. Solution: The problem might be elsewhere in the ignition system (spark plugs, wires, distributor, etc.). Further testing is required.

Replacing the Ignition Coil

If your tests reveal a faulty ignition coil, replacing it is usually straightforward. Refer to your service manual for specific instructions. Remember to reconnect everything securely and check for proper operation once the replacement is complete.

Conclusion

Testing an ignition coil with an ohmmeter is a valuable skill for any car owner. By following these steps and consulting your vehicle's service manual, you can diagnose a potential problem and avoid costly repairs. Remember safety first – always disconnect the battery before starting any electrical work. If unsure about any aspect of this process, consult a qualified mechanic.