[onfireX5]

Originally Posted by windtendo

I'll take a stab at this...

upper dp -> lower dp -> midpipe -> muffler -> tips

primary cats are on the upper dp
secondary cats are on the lower dp
cat-back systems include midpipe back to the tips
axle-back systems include muffler back to the tips

Removal of secondary cats (replacement of lower dp) won't throw CEL, but also doesn't do much performance-wise. More of a sound mod than anything.

Please step in if I've misstated anything...

Dead correct.