2008 BMW 535xi BATTERY DRAINING FAST NOT CHARGING

[ruvinsonfr@gmail.com]

My 08 BMW 535xi is not holding voltage in the battery. Im pretty sure it has a short to ground somewhere but I can't seem to find it. When I jumped the car since the battery is dead it would start up but as soon as you take the jumpers off the battery will drain in a couple seconds. If I charge the battery first and then start the car, it will start and then slowly drain the battery, so the alternator is not charging. I tried replacing the alternator with a brand new OEM Bosch one and still nothing. I noticed my ground cable on the passenger side was corroded out so I got a brand new OEM cable from bmw and replaced it. Still nothing. I have no idea where the short is coming from. any ideas how to find it?

[Machinecz]

It appears that there might not be an error in the diagnostic for BSD communication, but possibly an issue with IBS (Intelligent Battery Sensor)? When measuring voltage in the engine compartment, is it in the range of 13.8-15.3V? If the alternator is okay and the engine starts, the fault could lie in the control through BSD. In that case, it's possible to disconnect the thin wire from the alternator, and the charging should then work through the diodes, resulting in stabilized charging around 14.3V +/- 0.1V. This should be verified. If it still doesn't charge at the front, then there might be an issue with the alternator even if it's replaced. For anyone reading with the diesel version, there's a known issue with the vibration damper. It rotates, giving the alternator the impression that the engine is running at lower speeds than idle, behaving as if the car is starting and disconnecting the alternator. However, in the petrol versions, the vibration damper is fixed, and this issue doesn't occur. Just adding this information.