How to Test Ignition Coils

 

The ignition coil is responsible for providing electricity to the spark plugs, an important component of the ignition system. When a vehicle frequently stalls, misses or won't start at all, an ignition coil may need to be replaced. The good news is that a relatively simple test can determine if the ignition coil is having a problem. DIY testing with one of the following tools can help you avoid a pricy visit to the auto shop. If you do end up needing to replace the ignition coils, you can buy them online by visiting www.araparts.com.

 

Multimeter

This testing device can tell you if the resistance is out of specification, or if the coil is completely dead. While multimeter's are not very effective for a coil that misfires occasionally, it can definitely help. The epoxy (the black or white material that surrounds the actual coil) can have an internal hairline crack that might expand when the coil is hot. This can cause the coil to test out just fine, but misfire occasionally while driving around, towing, etc. You can purchase standard multimeter's just about anywhere, including Walmart.

 

OBDII

A regular OBDII (on board diagnostics 2 - good for all U.S. market 1996 and newer vehicles) scanner is great testing tool. You can find the misfiring cylinder with OBDII and the check engine light needs to be on. One sure way to tell if it is the coil that has issues is by swapping the coil from the misfiring cylinder to another cylinder and resetting the vehicle computer (this can be done with a scanner or by simply disconnecting the battery for 60 seconds). If the misfire follows the coil, you know it is the coil. If it doesn't, the coil is not the problem. These scanners start at around $5 on Amazon for the cheap Bluetooth versions for Android or iPhone and will more than likely cost you around $60 at the local auto parts store.

 

A Mode 6 Diagnostic.

This is a more advanced ODBII scanner that has mode 6 (non-continuous monitors). Not all cars have the same "test ID", so each owner would have to find out their own test id. A mode 6 diagnostic scanner is a very useful tool to find out what is going on with your vehicle, especially if there is no check engine light. Mode 6 data can help to reduce time consuming guesswork by eliminating systems and components as problems. They can also pinpoint the cause of intermittent misfires. That said, to get the most out of the mode 6 diagnostic data, it helps to have some knowledge of how the engine works. These start at about $100 online, and about $150-$200 and up at the local auto parts store.

 

An alternate way to test ignition coils is to use a "spark tester." You will be able to find inexpensive spark testers on sites like Ebay, Walmart, or at your local auto parts stores, starting at around $5.

 

Inline Spark Tester

This is a tool that connects between the coil and spark plug and is built to include a window that makes it possible for you to physically see the spark. In just seconds you'll be able to troubleshoot for spark and other issues, including dirty spark plug connections, defective points and bad connections or cables.

 

Regular Spark Tester

This tester basically does the same thing as an inline spark tester, except instead of connecting to the spark plug, it connects to any ground point on the vehicle.

 

DIY Ignition Coil Testing

This is a free ignition coil testing method that will only work if the coil is 100% dead. Here’s what you need to do - while the engine is running, unplug the connector. If the misfire gets worse, then that coil is good. If there is no change, then the coil is bad. It's imperative that when you carry out this test that only the harness connector is disconnected, and the coil is not removed. If the coil is removed/ separated from the spark plug while connected to the harness, and the engine is running, the high voltage has nowhere to go, except back into the coil and into the vehicle electronics system. This can damage the coil, and even the main vehicle computer. Any coil that is separated from the spark plug while the engine is running must be grounded somewhere.

 

The Best Method to Test Ignition Coils

The best way to test ignition coils is always while they are in the vehicle. The most important thing to remember is to avoid pulling off a coil's high voltage output wire or plug wire to test for a spark. Besides taking a chance on being severely shocked, a coil wire or open plug wire will increase the voltage requirements on the coil to the point where it may damage the coil. The safest way to test for a spark is to use one of the tools we’ve listed here.

Need to replace your ignition coils? Visit www.araparts.com (wholesale prices, free shipping and a 1-year warranty on all parts). Just have a question? Call the experts at (916) 585-6835 today.