How to replace and check a failed ignition coil

Today’s topic is how to replace and check a failed ignition coil. An ignition coil is responsible for sending power to the spark plug thus giving a spark. Without a functioning ignition coil, the spark plug will not ignite the fuel and air mixture in the combustion chamber. A bad ignition coil will cause an engine to misfire which will ultimately result in a loss of performance and shaky engine. Usually, one or more faulty ignition coil is enough to prevent the vehicle from starting or running properly. A faulty ignition coil will trigger engine code: P0300, P0301 P0302, and P0303, P0304 and so on. Moreover, it also depends which ignition coil has failed that can trigger a specific code. Some of the common sign of a failed ignition coil are rough idle, engine shaking, no start or difficult to start, one or more misfire, random misfire, hesitation and complete loss of power.

Here are some ways to check if you have a failed ignition coil. First, you will want to conduct a power balance test which will let you know which engine cylinder is not functioning properly. With the engine running and parked, simply disconnect one ignition coil at a time. A functioning ignition coil will result in a decrease in rpm and change in idle. That means the ignition coil is function and that coil should not be replaced. Continue to conduct the power balance until there is no rpm change when disconnecting the ignition coil. When there is no change in rpm that means that the ignition coil on the cylinder is faulty. In addition, you can also use a test light to test for spark coming from the ignition coil. Remove an ignition coil and connect the test light to the negative side of the battery. With the engine running, point the test light close to the boot/bottom of the ignition coil where it connects to the spark plug. If the ignition coil is good; there should be a spark. If there is no spark, that means the coil is faulty as long the connects and wires are good.

Next, you will need an OBD 2 scanner to confirm the ignition coil is faulty. This only works for vehicles 1996 and above. Locate the OBD 2 port which is usually located underneath the steering wheel, center console or by the glove box. Connect the scan tool and press the read code button. The scan tool will display one or more engine codes if the check engine light is illuminated. For example: Let’s say you disconnected cylinder number two and there is no change in rpm and let’s say the scan tool detected a fault in cylinder number two or P0302. That means the ignition coil failed on that cylinder. When replacing an ignition coil it is best to use original parts from the manufacturer and not aftermarket parts. Usually, an aftermarket part will not last as long as the original part.

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