When Your Ignition Coil Fails

If you’ve noticed that your Nissan Sentra has been behaving erratically and it’s not running as smooth as it had been, you could be looking at signs that the ignition coil is failing. The ignition coil is the component responsible for transferring power from the generator to the spark plugs. In turn, the spark plugs use this power to ignite the fuel and make your Sentra run. When diagnosing signs of ignition coil failure, keep in mind that the severity of symptoms will vary depending on which ignition coils are malfunctioning.

Signs Your Ignition Coil is Failing

Essentially, the ignition coil is what your car needs to move. It is responsible for transforming 12 volts into thousands of volts in order to ignite the engine’s air-fuel mixture. Since it’s job is to generate the ignition spark, any ignition coil problems could quickly cause issues with the performance of your engine. For this reason, it’s important to understand the signs of ignition coil failure.

1. Your vehicle is stalling.

If your ignition coil is going bad, your vehicle will emit irregular sparks to the plugs to keep it running. When this happens, your vehicle will shut off or stall when you come to a stop since it won’t have the necessary spark to ignite the engine. Essentially, no spark means no start.

2. The engine is misfiring.

If you try to start your Sentra with a bad or failing ignition coil, you’ll notice a very rough ride, including sputtering and coughing on a regular basis. When you drive on highways at high speeds, your car will spit and jerk, or if you are idling at an intersection or stop sign, it may vibrate and shake.

3. You have poor fuel economy.

Have you noticed that you’ve been getting less mileage for the gallon? If so, it could be a sign that your ignition coil is failing. When the spark plugs don’t get enough power, your Nissan will struggle and use more fuel in an attempt to compensate for the lack of power it’s supposed to be getting from the plugs.

4. Your vehicle won’t start.

If your vehicle is having problems starting, check your high tension leads that run between the spark plugs and the distributor. When your ignition coil fails, at least one spark plug isn’t receiving the correct amount of charge. If your vehicle won’t start in the cold, it’s a good indication that the ignition coil is failing. By running a test on the HT leads, you can verify that a spark is, in fact, traveling from each lead to each plug.

5. Your vehicle is backfiring.

One of the earliest signs of ignition coil failure is backfiring. Backfiring happens when the unused fuel is pushed through the car’s exhaust system. You may notice black smoke coming from the exhaust or smell gasoline. If left undiagnosed and unrepaired, you could risk significant damage to your exhaust, resulting in costly and unnecessary repairs.

6. Your “check engine” light comes on.

We have all experienced the anxiety that comes with an illuminated “check engine” light. When you have a damaged or bad ignition coil, your car may experience engine performance issues, namely misfires, which will trip your Nissan’s computer and cause the “check engine” light to come on. The light will also illuminate if the computer detects a problem with the signal or circuit in the ignition coil, including when a coil is shorting or burning out. Since the “check engine” light can come on for a number of reasons, it’s important to have a computer scan for trouble codes to properly diagnose the issue.

What Causes Ignition Coils to Fail?

Your car’s ignition coil is responsible for providing the high voltage the ignition system needs to fire the spark plugs. It increases the primary voltage from 12 volts up to thousands of volts. If a plug wire or spark plug has excessive resistance or is open, the voltage output could potentially shoot higher and burn through the internal insulation on the coil, causing a short. This typically happens at voltages higher than 35,000 volts. When your ignition coil fails, the voltage output decreases, and the engine will either badly misfire when under load or it may not start at all. The misfire may also move across the cylinders. Therefore, if you suspect ignition coil damage, it’s important to measure the primary and secondary resistance of the coil using an ohmmeter and determine whether the coil requires replacement. Although ignition coils can malfunction for a variety of reasons, the main cause of ignition coil failure is due to bad spark plug wires or spark plugs themselves. Other possible causes include vibration and heat, which can damage the insulation and windings of the ignition coils. If your Nissan’s engine is experiencing repeated coil failures, an underlying cause could be due to an excessive spark plug gap or resistance from damaged or worn spark plugs. In rare cases, ignition coil failure may be caused by a lean fuel condition that results from leaky valves.


If your Sentra’s spark plugs are worn, the ignition coils are forced to operate at a higher output. If the gap in the spark plug increases as a result of normal wear-and-tear, it could mean that more voltage will be necessary to create a spark in the chamber. In turn, increased voltage means that more current will need to flow through the primary circuit, which can ultimately overload your Sentra’s primary transistor. For this reason, it’s important to ensure that your spark plugs and any other components in the system are in optimum working condition to reduce the likelihood that you’ll experience ignition coil failure. As is the case with any part of your car, doing regular maintenance as recommended will ultimately save you money in the long run.