I am driving an '04 525i with 140k miles. I started getting this intermittent problem where the radio will go silent for a second, then the iDrive system will start reporting errors, usually some or all of:
Control Systems! Drive Moderately
Transmission Fault! Drive Moderately
Cruise Control malfunction!
Flat Tire Monitor malfunction!

The screen will go repeatedly black-out and the interior lights will go off (and radio off), then a moment later it comes back to life and continues to report the errors, over and over again. This 'rebooting' will continue many times for the first few minutes and then it will just steadily report the errors without the screen blanking. There doesn't seem to be an effect on power or the engine, although I notice that the car shifts differently after the transmission fault message.

Usually when I return to the car after parking, there are no errors/message - all systems normal. Later the same day or a couple of days later, the whole thing happens again. The OBD system will sometimes store pending codes, but they will clear as well. The codes I have seen when this happens are P1891 (If I get a transmission fault) and P0440 (once).

Any ideas about what's happening? Please help!

 

check your boot for water, but the short answer is your having a canbus fault, somehow somewhere the bus is going down, ecus cant talk to each other, loads of fault codes and warnings.

 

Have you checked your voltage. It could be the alternator going bad, battery or just as evolotion said water. I would start there. Go to advance auto or pep boys and have your alternator and battery checked if there is no water.

 

How old is your battery? When the battery starts to go on our cars, funky electronic things start to happen. As others have said, have your battery and alternator tested. You might just luck out and solve everything with a new battery.

 

Thanks for the suggestions. I don't see any water, I'll get the battery/alternator checked.

I started to think alternator yesterday when I noticed that the cabin blower speed was all over the place... which started before the errors started coming, and it continued to fluctuate and shut off during the whole ride. Strange thing is that driving an hour today with no issues...

 

Battery was replaced in June of 2013. If the alternator is bad, does the battery need replacement too?

 

No you do not need to replace the battery. if it is the alternator after replacing just drive around for a while and you should be good. to me it seems as if its on its last leg. let us know how it goes

 

I rigged a voltmeter to watch what's happening, and except for right after starting and when I come to a stop and the idle rpm drops a bit, the voltage is pretty steady @ 13.3V.

Strangely, I haven't had a problem in the last 5~6 days. I can't think of any reason why the strange errors would have stopped. I did move around the MPM when looking for water in the trunk, but nothing has really changed.

 

Another week passed without the error messages coming-up... There was one trip where my alarm kept sounding intermittently wile driving, but after restarting the car, it hasn't recurred. Also, I strangely notice that the fuel economy reported by the computer seems to be higher this past week. It used to be 18~19 MPG, now reading 22~23 MPG without any change in driving... Strange...

 

curious Do you know you car's history? Unless you have owned it since new maybe some water got in somewhere it should not have...?
Alternatively since you said you moved some of the modules in trunk have a close look at them again and see if there are any signs f corrosion