My check engine light came on on my 97 328i and I took it to the dealer. They said the OBD said it was a bad catalytic converter. Since they wanted $2200 for the part, I bought an aftermarket and had my mechanic replace the whole exhaust from the manfold to the exhaust tips. While he had it up I decided it would be wise to replace the Oxygen sensors at the same time. I bought two Borsch -one before and one after the catalytic converter. The light was off about a week and came back on. The OBD this time said :"BBH02S12 sensor heater circuit" Explanation Open or short circuit condition- probable cause - poor electrical connection, faulty H02s. My question is aren't there only two Oxygen sensors on the car? Since they are both new, I am guessing that there could be a bad electrical connection, or unlikely a faulty new part. Does anyone have any other ideas??