I did have that valve (#8) fail, but it did throw a code. They are not expensive. If it fails open, you get exhaust gas going into the air pump (#1) which will ruin it pretty quickly. I believe the pump should only run the first 60-90 seconds from a cold start, after that, the pump should turn off and the vacuum valve should close. It would take 3-4 hours sitting before the engine cooled enough for the pump to run again on the next start.

If you haven't done them, the little o-rings (#12) go bad, but I think they were part of what is replaced in the Beisan process.

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles