Hey guys, just thought I would add a little bit of my experience to this thread. I read this thread and took some advice. My symptoms- no “dinging” when I left key in ignition, no power to obd, no Power to tachometer, Brakes lights stayed on all the time. What I did to fix tach- checked voltage at fuse box for gauges. I had 12v. 10v at gauges. Thought that was weird. Went to the x15 connector, found some corrosion and started prying around. I found the voltage drop after that connector. I went to pull the pin out for the power for the gauges and it the wire fell off the connector. Luckily I had some extra pins and repinned that connector. Fixed the no tach power, the 10v at the gauges is now 12. It nows “dings” to let me know the key is still in the ignition AND fixed the brake lights staying on all the time. Started checking other wires and found two more that were so corroded they fell apart when I tugged on them. Not sure what they go to but I’ll know tomorrow after i repin them. Just thought I’d share, never count corrosion out of the picture. Corrosion causes me several issues and so far re-pinning one pin has fixed three issues. I’m hoping tomorrow I’ll fix the obd not working and whatever else the gray and red stripped wire is in the x15 connector

 

This thread, and others similar to it, were very helpful in all the different tips and things to check out. In my particular case, I had to replace my tachometer. The problem started a few months ago when I accidentally lost one of the two bolts that holds the tachometer to the steering column. I have upgraded all of the engine/transmission mounts to polyurethane, and I have more vibration throughout my '06 MCS as a result. It was about eight weeks until I was able to replace the lost bolt. However, in that time, I can only guess the solder joints of the plug that goes to the harness, or some other part of the tachometer, vibrated to the point of various issues. The initial problem was the low tire and DCS lights coming on. At first, it was only when it was cold out, like almost freezing. Then the issue started becoming more random, to include the tachometer digital display going out, the entire tach LEDs and needle going dead, to even having the issue with the speedometer going dead, engine temperature needle going to max temp, and the brake/ABS LEDs flashing. It eventually became a complete nightmare.

Of course, I replaced the DSC steering column sensor, and had a BMW dealership calibrate the replacement, but these did not fix the problem. I reseated the relevant fuses, checked for moisture damage in the area surrounding the fuse box under the dash, reseated the ABS sensors in the relevant tire wells, verified the battery was good, checked relevant ground wires, and tested and verified the voltage was good on the wire in the harness to the tachometer. In that time, I had ordered a used tachometer. Tonight, I finally had the chance to diagnose and replace it. A test drive helped verify the issue was gone, as the "Christmas tree" effect I was experiencing was no longer random but occurring almost immediately after startup.

I guess this is one more reason that the polyurethane mount solution is not the best. It would be better to purchase the Vibra Technics solutions.

 

Thank you all for your input on this. I had this happen to me today. Left the house for a music lesson, when I fired up the car to go home, no steering wheel tach. Looks like tomorrow I'll be scanning for corrosion. Like others, my car has done a bit of sitting as I havent been driving it much the past 3 years, but I try to get out and drive it least once or twice a week. My car stays in the garage 100% of the time when it's at home, so I cant imagine any water type issues - but with the details in this thread, I'm going to start chasing corrosion, starting at the kick panel fuse box on the driver side. I found a good video on youtube where a guy did the same troubleshooting mentioned above, also leading to that large wiring harness connector at the bottom of the fuse box. Of course something like this will happen when I have my car up for sale LOL - it wants me to keep it I suppose :D

This guy has the exact problem I have and this is where he found the corrosion. The video will start at the fuse box, if you are interested in all the pre checks he did, feel free - lots of good info here.

 

Welp, no corrosion anywhere and the main harness connection at the fuse box looked clean as a whistle. There were no codes shown on my obd2 scanner either. When I connect the tach while the car is on, the needle will go down, and then go right back to 0. I've ordered a replacement tach to see if maybe mine just went dead :(. We'll see.