A customer was recently referred to us with a recurring issue with his R60 mini, periodically the engine malfunction indicator would illuminate and the vehicle lost power. His regular garage recommended us to investigate, I had known the proprietor of his regular garage for many years, actually back to attending the same college as apprentices so was happy to help.
Although the engine management lamp was not illuminated whilst in our custody we began by retrieving any stored error codes. There were three historical codes stored, 4862 (Air system/egr plausibility) 41BA (Exhaust back pressure sensor) and 497D (Exhaust pressure sensor before turbo signal not plausible). Of the three codes set 41BA had a frequency counter of 33 and was the more prevalent so I began with the exhaust back pressure system.
Unfortunately I could not read the back pressure sensor signal through live data so connected a scope to the signal wire through a break out coupling, the signal was flat throughout the rpm range so would appear to indicate defective sensor and/or activation. The exhaust back pressure sensor measures pressure between the exhaust of the engine and the turbine wheel (Exhaust side) of the turbo (Not to be confused with the dpf differential pressure sensor). I removed the sensor to enable examination of the pipe or tube which runs to the exhaust, In my experience it is normally these pipes that become blocked as opposed to the sensors themselves.
I sprayed a small amount of releasing oil into pipe which quickly settled and did not drain away indicating the pipe was blocked. A new pipe was installed an extended road test carried out and vehicle returned to customer who incidentally called us a few weeks later to report he had experienced no further problems with the car.