How to Replace Ignition Coils
Without a properly working ignition coil, your car will run poorly. Symptoms related to a failed ignition coil include a flashing/illuminated Check Engine Light (CEL), misfires, jerking sensations, rough idle, reduced fuel economy, and increased emissions.
If neglected, unburned fuel entering the catalytic convertor can cause the converter to overheat and damage the metal alloys inside. This same raw fuel can also ‘wash’ oil from the piston rings and cylinder wall, causing accelerated wear to your engine. If you are experiencing these symptoms, the problem should be fixed as soon as possible.
Replacing an ignition coil is a basic repair procedure you can do at home with tools from your local AutoZone. That being said, many of today’s vehicles, especially with engines positioned sideways, can make testing/changing an ignition coil a bit more complicated. Check out this guide and learn what it takes to do the job right.
How to Change Ignition Coils
Ensure the engine is cool, apply the emergency brake, and open the hood. Disconnect the negative battery cable before working on anything else. Note: Check the vehicle's repair guide first before disconnecting the cable. Some vehicles will react negatively when the battery cable is disconnected, especially for an extended period. A memory keeper/maintainer can be used but check first to avoid electrical damage or other headaches.
Remove the Ignition Coils
Ignition coil replacement can be challenging on some vehicle's engines. The greatest obstacles you'll face is accessibility and sticking components such as the ignition coil insulator boots sticking to the spark plug and tearing apart during the removal process. Some ignition coils can be difficult to reach and require removal of the upper plenum/intake manifold. In these cases, a new plenum gasket will be needed. Check the Repair Guide for your specific vehicle and engine.
Once the ignition coils are located and accessible, carefully disconnect the electrical plastic pigtail connector to avoid damaging it. In some instances, due to age and deterioration, the plastic connector will break. Replacing the connector can be challenging so be prepared and use care. Next, unscrew the coil hold down bolt(s) and remove the coil. A twisting motion is usually necessary to make the insulator boot slide off the spark plug. If it tears away, you will need a pick and/or needle nose pliers to remove the stuck portion from the spark plug. Be careful not to damage the spark plug porcelain as this will cause a misfire and you'll be right back where you started after the work is completed. If replacing more than one coil, it's always a good idea to replace each one at a time. If removing two or more at a time, identify each coil pigtail connector with stick on numbers or take a picture beforehand. Once the coil is removed, inspect for oil or antifreeze contamination on the boot and inside the spark plug well. If present, the leak should be repaired to avoid future damage and a repeated failure of the new component.
Test Each Ignition Coil with a Multimeter
If your vehicle's CEL was flashing, most likely there's a misfire code stored in the PCM (the car's computer brain). Use a code reader (or drop by your local AutoZone) to read the code. In most cases the code will identify the culprit cylinder with the misfire. Note the term “misfire”, not “failed coil”. Misfires can be caused by many reasons. Related ignition system parts such as a spark plug, or fuel system component such as a fuel injector, a vacuum leak, or even an internal mechanical engine problem creating low cylinder compression, are potential sources for miss-fire symptoms. Ignition coil failure is common but if in doubt, there are a couple of options for testing.
If the coils are easy to access, try swapping the suspect coil with another coil on the engine. If the misfire “follows” the suspect coil to the other cylinder, the coil has failed. If this is not feasible due to limited access, use a multimeter and test the primary and secondary winding of the coil. If you're not sure how to do this, refer to our guide or drop by your local AutoZone. If you get a reading that's outside the normal range, you'll need to replace the coil. The owner's manual should list the normal resistance range. Now that you know if the coil (if any) has failed, you are ready to install the replacement. Before doing so, it's a good idea to remove and inspect the spark plug. Again, check for contamination and repair any oil or coolant leaks. Also, check and remove any debris in the spark plug well.
Lubricate the Coils Install Them
Verify you have the correct coil. Compare the length and pigtail connections and terminal pins. Then, apply dielectric grease to the inside tip of the replacement ignition coil insulator boot/shield. This will ensure a good seal against moisture and aid removal in the future. Carefully install the coil, pushing it onto the spark plug. Next, re-install the coil hold down bolt and then cautiously reconnect the electrical pigtail. A very small amount of dielectric grease may be used and may be applied to the coil or the pigtail/connector. Ensure the connector fits snugly and you feel the connector tab engage and lock onto the coil.
Check Your Work
Re-install the remaining components. Attach the negative battery cable, start the engine, and take your car for a test drive.
Once you are certain the problem has been corrected, clear the trouble codes.
If your vehicle has bad ignition coil symptoms, it’s time for a little do-it-yourself action. Grab the tools needed at AutoZone and make sure to test and replace any failing ignition coils before your vehicle breaks down completely.