I'm sure it does work, unless you have a crack in the pipe.... in which case I'm not so sure. Anyway, after a bodge job with goo, glue, a bit of aluminium sheet and a few clamps, mine passed its MOT this morning despite its cracked EGR pipe. (Phew!) I'll look again in the coming days and consider a proper 'delete' now it won't be tested again for another year.