The installation of catless downpipes on your will result in an inevitable check engine light (CEL) as the DME will detect that emissions are not being burnt-up by the OEM catalyst.  To remove this CEL without having to tune it out we offer the CEL Delete Kit which is comprised of two O2 sensor spacers specifically calibrated to comply with BMW's parameters for a functioning catalyst.  These install into the post-catalyst O2 sensor bungs on each Downpipe, effectively removing the CEL that would otherwise appear.