If anyone knows anything about bad o2 sensor on the caldina st215. Today mine started running rough an running rich an smoking an the code came to be 21 witch is bad of sensor. Could that cause it to smoke an run like that?

so what happened when you changed the sensor ?

and in answer to your question yes the computer doesn't know what to do so your A/R is off and comp keeps trying to compensate

It just happened today so haven't got a sensor yet gotta order one.