Originally Posted by Pistratoaie

What about registering the battery when you changed it? when we changed our X5 battery all sorts of warnings went off, until we drove it to the shop to get it registered and that solved everything. otherwise it does sound like the alternator could no longer be sufficiently charging the battery and once the battery has been discharged it will do mysterious things.

Originally Posted by pcy

There is a relay in the trunk that can contribute to no-start condition. That relay has a diagonal line on the face. I think it's black color relay.

Originally Posted by scottalexander

When these cars don't start do the obvious:

- unplug the IBS sensor and try to start it
- unplug the MAF sensor and try to start it
- DME is not aligned or got un-sync’d to the CAS (use ISTA)
- brake light switch is faulty
- braided ground cable faulty
- positive cable on battery has separated at metal conjunction and not connected
- fuse in eBox under the hood is blown
- crank shaft sensor is malfunctioning

Step one:

- get ISTA

Originally Posted by Awest91

Ok so I have an 08 535i with sport package and iDrive and i have a very frustrating problem going on.
(Please don't reply if you're going to say something negative, I have had enough headache dealing with this. Thanks)

Ok first off (This may or may not be the cause of the problem but most likely is) About a month ago I installed a very high powered aftermarket subwoofer and amplifier by tapping into the under seat subwoofer wires that run back into the trunk for the low level bass signal, the positive and negative terminal on the battery for power, and the cigarette lighter fuse in the trunk for the remote turn on.

Everything worked perfectly fine (I know a lot about car audio I've been doing it professionally for many years so I know it wasn't an installation related mistake) and after about 30 minutes of driving listening to music the car threw a few warning messages on the iDrive.

1. transmission malfunction: functionality or display of gear selector position may malfunction. It may be possible to engage a gear without depressing brake pedal

2. DBC malfunction:
Dynamic brake control (DBC) is not active during emergency braking. Drive with caution

3. Drive control system!:
Driving stability
Drive control system malfunction. Reduced driving stability in curves. Drive moderately

So I pulled over to turn the car off and back on to see if it would go away but when I tried to start the car again it wouldn't start and continued showing the same messages along with the "P,N,D,M/S" lights on the gear lever fading/dimming. (Btw I have the electronic gear shifter, not a normal one where you manually move backwards and forward to put it in park/neutral/gear) I tried having a someone jump start it, I checked every single fuse, looked by the battery and under the hood and saw nothing out of the ordinary. I got the car towed home and the next day I decided to remove the amp and sub to see if that fixed it and it didn't at first but about 2 days later I randomly went outside and tried to start it and it started right up with no warnings or any problems at all.

So I'm driving the past few weeks and I decide to put in a smaller amplifier and door speakers (how stupid of me, I know, but I figured the power draw from my 13.5" JL audio subwoofer and 1000w amp was too much and this normal size set up would be fine). Install went fine again, I drove around for a few days and parked the car at home one day, went out later to start it and same thing. All the same warning messages so I removed the smaller amp and door speakers and returned everything back to how it was but this time it's been close to a week and it still won't start.

I tried unplugging the battery, checked all fuses, checked everything like last time, and then again to make sure I didn't miss anything and still nothing. I bought an agm safe battery charger and charged the battery hoping it would fix it, still nothing. A few days have gone by since and I got in the car yesterday and saw a few new messages along with the same ones that have been on this whole time

The two new ones are:

Start-off assistance:
Start-off assistance inactive caution, vehicle may roll back

Battery charge level low:
Battery heavily discharged. Charge by driving for a longer period or using external charger


And also, I just bought the Bavarian technic obd2 tool about 2 months ago and I've looked on there at a few things but this is the first time I've ever used it so everything is still kinda new/confusing but If you guys have any suggestions/ideas I can extract info or real time values off of there to see if that's the reason/cause

Thanks in advance