leetheleo

There is an oxygen ( O2 ) sensor in front of/upstream of and behind/downstream of the catylitic converter. What is the function of each sensor? I'm assuming they are fuel mixture and some type of error code for the catylitic convertor. When controlling fuel mixture are both sensors used to adjust fuel mixture? Is only the upstream one used for fuel mixture? Is only the downstream on used for fuel mixture? Are there any other functions for each O2 sensor? 2000 c230 kompressor
Thanks in advance