Possible solution for CEL when using headers on 2000+, an O2 spacer with a mini-cat..

[spendy]

My '06 cayman S has headers with hi flow cats and I get cat efficiency codes with them. I've tried both the regular spacer and the mini-cat spacer and neither of them worked in my case. It may be a different story in the earlier cars. My '98 spec boxster has the secondary O2's hanging in the breeze and does not set any codes.