Hello! I have a 95 sc300 with the CEL on. I decided to check it myself to see what it was since I need to get a smog check. So, I have a code 21. From what I understand code 21 is the Main O2 Sensor and Heater Signal. Now my question is, is it just the O2 sensor or could it be the heater signal?(Not to sure what that is?) Or am I just making this more complicated than it is and all I have to do is change the O2 sensor? If someone could help me out with this question I would really appreciate it! Oh, and I did a search to see if anyone had a similal probelm but was unable to find any. Thank you!

Matt

 

Help, anybody?