I have a recurring CEL, i keep clearing it, it keeps coming back.. I have replaced the pre-cat O2 sensor twice now..


Is the code 21 specific to either sensor? Perhaps I should be replacing the post-cat sensor?

 

How are you getting your code?

You have a 97.. this would be an OBDII system and usually a 4 digit fault code read from a scanner.

The two digit codes would be OBDI through 95 model year.

 

I am getting the code by clicking the ignition switch on/off/on/off/on
Then the CEL flashes a 21 and a 55, and the odometer digits also report 21, then 55

I also get an O2 code from an Autozone scanner, not sure if it is 21, but it is an O2 code..

 

I did not know that was possible on an OBDII.. thanks for enlightening me.

If the wiring on the 02 you already replaced is good i'd consider swapping the other sensor.

 

that's what I did earlier today, hopefully the CEL will stay off now, I have driven it about 40 miles and had about 5 key starts, so far, so good...