The generic OBD-II readout for code 1430 is that the catalytic converter is not functioning properly, as indicated by the downstream O2 sensor. So--- sounds like at least one of your O2 sensors is failing. Of course, the BMW specific OBD-II code could be something else...

How many miles on the car, and why did you have the alternator, etc. replaced?

Thanks,
Randy H
'01 X5 3.0i 5-Spd