O2 Sensor on OBD2
 

are both O2 sensors on header and cat required on OBD2 cars? my cousins CEL is on and he's only using the O2 plug on the manifold.

Re:O2 Sensor on OBD2
 

yes both are heated and yes you will throw a cell if its not there. if its an OBD 2 ecu it needs the 2 o2's