This post is titled exactly the same as the original discussion found on E90Post.
I am renewing the discussion here because it applies to our cars and members looking for help may not think to go looking at E90.
The computer module that controls our engine is called an MSD81. It is the same one used in the 1 series, E8x, E7x, E9x that have the same engine.
The cover is opened by simply prying open bendable tabs and this is the inside:
This problem just occurred on my 535 but, again, I am sharing the experience here because it applies.
My symptom of a failed DME was a sudden lose of power, very bad shaking, and rough engine idle. A classic symptom of not running on all cylinders.
As bad as the engine was running, I new this was not a simple misfire and check engine light.
My code reader reported misfire on cyl 1,2,3 or a failed DME. I checked my plugs and there was no fouling of fuel, oil, carbon, etc, everything looked perfect.
Here is where you need to pay attention:
With these symptoms, the dealer would first go through replacing plugs, then injectors - the newer injectors can't be mixed with the old design so you will need to get all 6. By now you are ~$1,500 into the repair at least and still have not resolved the problem. When they finally decide it must be the DME (after all, they will swear they have never seen a failed DME), it will be a $1,300 part then they will need to program it, probably another $300.
So...
I was already familiar with the "Failed DME" discussion and skipped all other troubleshooting and went straight to testing my DME. The test is a simple continuity check of the 6 MOSFET chips that drive the Injectors.
Sure enough, the MOSFET for Injector #1 was bad. The replacement part costs $1.07. I purchased 6 of them, then paid shipping so I am ~$15.00 into this repair so far.
At this point, you can solder your own if you do that sort of thing or find any electronics repair shop that will do the soldering for you.
After we replaced the MOSFETs, I plugged in the DME, and car started/runs perfectly.
Check out the longer discussion on E90Post. You will find posts/video on how to do the continuity test and MOSFETS that people have ordered.
http://www.e90post.com/forums/showth...5#post12539075