O2 sensor after the muffler

1999 Cav. check eng. light on, code calls up O2 sensor after the muffler, replaced it light came back on replaced it again and light came back on. is there something else that can cause this code? or am I down to putting black tape on the dash over the eng. light.

Maybe sensor is not bad, but telling the truth? :2cents:

What code was it exactly? The post-catalytic converter (not muffler :)) O2 sensor monitors the cat efficiency. If your code was p0420 (cat. efficiency below threshold), then most likely you have a bad cat. If that's it, you should still check the upstream O2, if it's reading lean and the PCM is commanding rich, then the post-cat O2 may be seeing that extra fuel and "thinking" the cat's bad. The PCM basically just compares the two to see how the cat's doing.