Glad it is helpful. I don't know if urea is used for regeneration or not. I know urea is used to promote a specific reaction in the catalytic converter to reduce NOx. The DPF is regenerated by injecting extra diesel late in the injection cycle which raises the DPF temperature and oxidizes the accumulated soot mass. I think that's the active regeneration mode. Another method is to send NO2 through the DPF which somehow helps. Maybe that's the passive method? It might use urea for that. I don't know for sure how BMW does it.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim