Initially I kept getting a CEL due to the pre-cat O2 sensor being bad, so I replaced it and that took care of the light. However, the light came back a few days ago and this time the error is 16804 "Catalyst Efficiency Below Threshold" and I'm getting an error about the pre-cat sensor again. The sensor is brand new, and the exhaust is a Neuspeed with a 42DD downpipe with a cat. The rear sensor is spaced out with two spacers, so I don't know what to do about this one.

 

i had the same problem before, im not sure if your supposed to space both sensors you should ask cincytt about this one.