Is Your Ignition Coil Failing?

The BMW X5 combines luxury with strength in a mid-size crossover. It features strong performance from every trim, a comfortable and luxurious interior, a huge list of options for full customization and an efficient diesel engine option. The X5 debuted in 1995 and presented the change for crossovers from a light truck body to a car platform. Now in its third generation, the X5 gives drivers a range of engine choices from a 3.0 liter inline six turbo to a 4.4 liter V8 twin turbo. Like all BMW performance vehicles, the X5 benefits from regular maintenance and prompt replacement of worn parts. If your X5 is displaying erratic behavior in starting or running, you may have ignition coil failure.

What Is An Ignition Coil?

Ignition coils can also be called spark coils and their purpose is to transform the low voltage of the battery into the high voltage required by the spark plugs in order to ignite the fuel. Some ignition coils feature an internal resistor, but others have a resistor wire or an external one to put a limit on the current that goes into the coil from the vehicle's voltage supply. The wires connecting the ignition coil to the distributor and then from there to the spark plugs are known as spark plug wires. In earlier versions, all ignition coils needed breaker points with mechanical contact as well as a capacitor. Modern electronic ignition coils have power transistors that give the ignition coil the pulse it needs to work. Modern vehicles often have one coil per cylinder in the engine, or sometimes pairs of cylinders. This allows for less error from faulty spark plug wires. This type of ignition system is not needed at all for diesel engines as they start under compression to ignite the mixture of air and fuel.

How Do Ignition Coils Work?

Older ignition coils were constructed of varnish and high voltage windings insulated with paper. These were then put into a steel can and then further insulated with oil or asphalt to keep moisture out. Modern systems put the coils in epoxy resins that keep any gaps from penetrating the windings. Single spark systems have one coil for each spark plug. To keep sparking from happening early in the process, a second spark gap is built into the coil to keep a reverse pulse from forming. In dual spark system coils, you'll find two terminals on the secondary winding and each of those connect to a plug. There's no need for an extra gap or diode on this system.

When you look at a basic ignition coil, you'll see an iron core with two copper wire coils around it. As previously mentioned, these are put into a can or cylinder to protect them. Current from the battery goes into the main ignition coil winding and causes a magnetic field to form in the core. When the current builds up to the required level, a contact breaker opens, allowing it to send spark to the plugs. In a lab, only one millijoule is needed for each plug. However, in real engine conditions, the coil needs to compensate for factors like plug fouling, leaks, wiring loss and rich or lean mixtures of fuel and air. Because of this, the energy delivered is much higher than what is technically needed.

Symptoms of Ignition Coil Failure

If you're experiencing erratic behavior from your vehicle in starting and running, then the ignition coils could be to blame. The symptoms and their severity depend on which coil is failing. Take a look at the following six vehicle behaviors of failing ignition coils.


This happens when unused fuel comes out through your exhaust system. The explosion can damage your exhaust eventually if not fixed. You might also notice black smoke coming out or smell a strong odor of gasoline. Backfiring is an early symptom of ignition coil failure.

2.Difficulty Starting

If your vehicle is having a difficult time starting, especially in cold weather, this could signal ignition coil failure. What happens here is that a coil is failing and causing one or more spark plugs to not receive the appropriate amount of spark. The high-tension leads that run between the distributor and the plugs can be tested to see if there is spark running through them.

3.Bad Fuel Economy

If you notice that your fuel economy has gone way down, it could be related to ignition coil failure. In this case, because of the lack of power going to the spark plugs, the engine has to use more fuel to compensate.

4.Engine Misfire

When you have ignition coil failure, you'll start to notice less smooth operation from your car. Your engine might make coughing and sputtering sounds and jerk and spit at high speeds. When you're at an idle, it's likely to vibrate and sound rough.


With failed ignition coils, less spark is making it to the plugs. This could cause your vehicle to actually stop running. This happens most often when you stop the vehicle. The RPMs go down and the vehicle may simply shut off.

6.Coil Failure

Another problem is with worn spark plugs. If your spark plugs are worn, it causes the ignition coils to work harder. The more power they have to put out, the faster they will fail. This is why it's important to check your spark plugs on a regular basis to make sure they're not worn. Ignition coils should last up to 100,000 miles and sometimes even longer, but the average copper spark plug only lasts about 20,000 miles.

Visit to find all the replacement OEM parts you need, including X5 ignition coils. Unlike generic aftermarket parts, our OEM BMW parts are tested against strict performance standards and guaranteed to fit your exact vehicle. Don't compromise your X5's performance and reliability by using aftermarket parts. Search our site with a VIN, part number or keyword, or select your vehicle from the menu. Our BMW parts experts are available to help you find exactly what you need.