Help!

To those of you who are into the electronic control features of the E 46 I need your help. I have more lights coming on and going off and charging system malfunction problems than I can track down. Here is the situation. The service light came on and I plugged a diagnostic tool into the car that included BMW codes. It said I had a low heater voltage on one of my oxygen sensors. OK, I replaced them as at 100,000 miles I needed to anyway. But that didn't cure the problem. That was no surprise. I need to track down the original source of the problem (the ECU?) But even before the service light came on I noticed that the alternator wasn't putting out the necessary voltage and the battery wouldn't hold a charge. So I replaced them. I started the car up after this and the ABS light was on now, the red alternator light was flickering and the charging system was the same as before I replaced the alternator and battery. My Bently's doesn't help me on this one. Can anyone out there help?

Thanks