I have put together this guide to who ever has a BMW 3 Series E46 equipped with the N42 engine with a sudden hesitation, rough idling, misfire, lack of performance, engine light issue. There is no reason why you should not try to fix this problem yourself, the replacement part is affordable and it's straight forward to fix if you are handy with a screwdriver.
BMW has become aware of a potential problem that could affect the durability of Bremi ignition coils of certain models to fail prematurely. The affected vehicles may have a Service Engine Soon light illuminated with misfire faults stored in the Engine Control Module (DME) and a rough running complaint. BMW E46 models utilize one fuel injector per cylinder. Over time, these injectors can become restricted or fail electrically. If you have an injector giving you a problem, I suggest replacing them all. Potential problems include stalling, sputtering idle, cold-start issues.
In my case the first ignition coil failed at 60k miles, and the second one at around 70k. First time round I replaced only one coil so I was running 3 Bremi and 1 Bosch, and can confirm I had no issues, and fuel economy was the same. Second time round I went ahead and replaced the remaining coils.
Time & Difficulty Level
30-45minutes - Easy
Required Tools and Parts
- Bosch Ignition Coils #0221504464
- OBD2 Reader (optional)
- T30 Torx Driver
Replacement part is about €35 per ignition coil.
- Remove the cabin filter cover by releasing the 3 pins.
- Unclip the wiring from the front of the cabin filter tray and unscrew the 4 T30 Hex screws.
Note: unwind the last bit of teh screw by hand to avoid screw falling out of reach.
- Remove oil cap and slide out the plastic valve cover. Re-attach the oil cap to avoid any debris falling into the system.
- Lift tab covering the injector slowly until clip disengages and remove the clip.
- Pull out injector by lifting it up.Tip: using a screwdriver as shown will help you pull out the injector.
- Replace with new injector, make sure the injector is firmly in place and clip is secured.
- Run engine to make sure everything is place and not misfiring.
- Repeat steps 4 - 7 for the other injectors.
Fortunately I have a OBD2 reader handy to pinpoint the exact cylinder giving the problem, and if you run a diagnostic your resulting code might be one of the below:
- P1342 / P1343 - Misfire During Start Cylinder 1
- P1345 - Misfire During Start Cylinder 2
- P1347 - Misfire During Start Cylinder 3
- P1349 - Misfire During Start Cylinder 4
If you are going to change only one ignition coil and don't have an OBD2 reader you could swap the coilpack with another cylinder if the fault jumps to another cylinder you have your answer.
When installing everything back in place, make sure the airflow arrow on the cabinfilter is pointing upwards.