Hi - My "Service Engine Soon" light comes on from time to time. There is no rhyme or reason to when it's on and when it's not. Sometimes going over a bump will actually turn this light off. I have checked the codes and they are 12 (which I know is nothing to worry about) and 21 (O2 sensor - upstream or downstream from catalytic converter). The thing that I'm wondering is why do I sometimes get the 21 code three times? It started out as one 21 code then went to two of these codes and now three. I figured that maybe there would be one for upstream and one for downstream. Any ideas on this? Thanks.

 

If the PCM sees the code more than once, it will trigger it again. Hence, the reason for 3 code 21's. How is the car driving? I'd check the wiring to the upstream O2 sensor.

 

Hi - Thanks for answering. It runs good. It's good to know that it's just a duplicate. Thanks again.

 

According to Allpar, codes are not repeated http://www.allpar.com/fix/80s-codes.html


But my Neon flashes code 21 three times also

 

Hi - Thanks for the reply. At least mine isn't the only one that does that.