I know everyone says the Bosch O2's are crap, I currently have a pair of Bosch O2's on my Z. I'm just curious as to how they generally go bad. Do they normally start reading too rich or too lean? Do people notice the problem with the SES light goes on? Or when the car starts running out of wack?

My BLM's are a bit too low, and am wondering if it could be O2 related.

 

I am not aware of Bosch-specific O2 sensor's symptomps. I had them on my car before without any problems