I find the work that "Fluid Motor Union" does quite interesting. I especially enjoy their skills at metal working.... go figure (check out some of their projects if you're unfamiliar with their work). Anyway,they put out an education blog on automotive systems from time to time. The latest has to do with exhaust systems in general. Sometimes MINI owners have engine issues and throw CEL's (Ckeck Engine Light), and are frustrated with them re-appearing when it's assumed the problem was fixed. The car's computer runs a series of checks that are to be performed under very specific conditions (such as keeping the engine RPM's under a given point) or the "self check" is stopped and CEL's re-appear after the codes were cleared. So if this applies to you, then read on..... Fluid Motor Union » Education Station: Emissions and Exhaust