BMW Repair: BMW 323i, pollution control system, o2 sensors

Question
I just bought a 323i and i have done lots of repairs on it. Currently it is showing "service engine soon." Please tell me what I can do to fix it. I had some problems with the coolant system, but I have already fixed it. My car is not overheating. I just don't know why it's showing "service engine soon." I took it to the dealer and they don't know the real problem to this.

Answer
you should be able to check this for free with an OBDII meter from most parts stores.  They will lend it to you to check your car in their parking lot.

Likely something associated with the pollution control system.  Get it checked.  Could be anything from misfiring to O2 sensors.