DIY – BMW Z4 (E85) ignition coil replacement

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September 28, 2017 by quirkyuncle@gmail.com

Replacing an ignition coil is an easy DIY task that requires minimal tools and skill. You can easily complete the entire job in under an hour.


If your BMW suddenly starts running poorly, triggering the check engine light, the problem could be a failed ignition coil. Fortunately, this is a simple and inexpensive repair (mine cost under $25).

The six cylinder Z4 3.0i has six ignition coils, one per cylinder. Typically, these coils fail one at a time.

Many people recommend replacing all the coils as a set. I am cheap and only replaced the one that failed. If you are changing coil types or manufacturer, you must replace all of them at once.

Since the car ran so bad with one failed coil, and I was only replacing one, I ordered a spare and keep it in the trunk. The car has been running great with only one new coil for several months.

Note: While this procedure describes ignition coil replacement for a 2007 BMW Z4 3.0i (E85), the same process is applicable to other BMW models. The main difference being access to the rear of the engine.

This topic contains:


Tools and Time

  • Tools: 5mm Allen wrench (to replace), OBD2 scanner (optional for diagnosis)
  • Parts: Ignition coil
  • Time: 60 minutes
  • Difficulty: Easy

You can purchase a single 5mm Allen wrench or a set of metric Allen wrenches from Amazon.com.


Diagnosing the problem

Rough running and a check engine light are problems best diagnosed with an OBD2 scanner. See DIY – Help! My “Check engine” light is on! for information.

You can see a list of OBD2 readers that I’ve tested at OBD2 reader reviews, each review has links for ordering one.

In my case, I had a P0302 fault code for cylinder 2 misfire.

P0302 failure code

Searching online, common causes of this issue in a BMW Z4 are a faulty spark plug or ignition coil. Since the spark plugs had been replaced recently, it was likely a faulty ignition coil.


Ordering the parts

Note: There are two different types of ignition coil used in the 2007 Z4, manufactured by Bosch and Delphi. These coils cannot be mixed! If your car has one type of coil and you can only find the other type as a replacement, you will need to replace all coils in the car.
If you are not sure which type of coil is in your car, remove the engine cover, as described in Replacing the coil, to verify your coil type.

You can purchase a Bosch Ignition Coil or a Delphi Ignition Coil from Amazon.com. Verify part compatibility with your specific vehicle before placing the order.


Replacing the coil

Complete the following steps to replace the ignition coil:

  1. Remove engine cover

    There are four 5mm Allen bolts securing the engine cover. Remove these bolts and lift the engine cover from the top of the engine.

    Z4 engine cover

    Note: The low hood line of the Z4 provides unrestricted access to the top of the engine. For other BMW models, components such as the cabin filter housing might need to be removed to access the rear of the engine cover and rear ignition coils.

  2. Locate the coil to replace. Coils are numbered from 1 to 6, from front to back.

    Mine was the coil 2, second from the front.

    Z4 coil locations

  3. Lift and rotate the locking lever to disengage the coil electrical connector.
    Lift coil lock
  4. Grasp the connector housing; then, pull and remove the coil connector.
    Disconnect coil
  5. Grasp the top of ignition coil and twist it slightly to break the seal between the coil rubber cover and the engine. These two components tend to stick together over time.
    Twist coil
  6. Pull up on the coil and remove it from the engine.
    Coil remove
  7. Make sure that the coil you purchased the correct brand. Mine was a Bosch coil, as seen on the side in the photo.
    Identify coil
  8. Orient the coil so its electrical connector is facing in the correct direction; then, insert the ignition coil and push it down until it is fully seated.
    Coil insert and seat
  9. Connect the electrical connector.
    Coil connect
  10. Rotate the locking lever into place to fully seat the electrical connector.
    Coil lock
  11. If you have an OBD2 code reader, use it to clear the failure codes.
  12. Start the car to make sure that it runs well and, if you have an OBD2 code reader, that no new failure codes are generated.
    Codes clear
  13. Replace engine cover and secure with six 5mm Allen bolts.
    Z4 engine cover

If you do not have an OBD2 reader and the car runs well after replacing the ignition coil, the failure codes should clear and extinguish the check engine light after driving for a while. If the car does not run well after replacing the ignition coil or if the check engine light remains on, the ignition coil you replaced was not the problem or there is an additional problem. Try to Diagnose the problem again.

Drive happy!

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