Hi,
I've searched through previous posts on tips for installing the pre-cat O2 sensor. However, still looking to see if anyone can help out:
I have a stock 1997 528i that I bought about 8 months ago. It has 90,000 miles on it and I wanted to go ahead and replace the pre-cat o2 sensors.
However, I am still a bit confused - the diagrams in my Bentley's manual are different that what I see. Also, seems to be different from the different posts I've seen.
There is a black box on the driver's side, but not the passenger's side (I've read there should be a black box on both sides??). From this black box, 2 cables run to the front of the car and somewhere up into the engine. The other 2 cables run over to the exhaust system. The cables run to about the same place, with each O2 sensor plugged into what appears to be an area of the exhaust AFTER the catalytic converter. So, I have to assume these are the Post-Cat O2 sensors? If so, then how the heck do I replace the pre-Cat sensors? Or, am I wrong and what I'm seeing are really the pre-cat sensors?
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Pre-Cat O2 Sensor Question
I guess the reason why I am smiling while posting this reply is I went through the same thing not to long ago. My check engine came on for bank 1 pre cat O2 sensor. I refered to my Bentley and was confused about the diagram layout. If you follow your manifod from the engine and were it elbows down you will find the pre cat sensor. You can't see them from above but they are visible from under the car. your connector for the sensors are located under the cover plate on top of the engine just above the spark plugs. Just remember to remove your oil cap while removing the cover. Hope this helps if not too late.