Z3 1997 M44 ODB code P1423 Secondary Air System

The air pump was replaced by the previous owner. Now, about 6 months later, I am getting these codes again. Are there any common problems associated
with this system? I am suspecting a sticky vacuum vent valve. Any ideas?
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Leonard
Eloquent profanity, it rolls right off my tongue...Lowell George
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P1423's are a classic Z3 problem.
The key is to replace both the check valve *and* the air pump, not just the air pump. The check valve is root of the problem: it's letting water vapor from the exhaust manifold flow into the pump, which is corroding the pump.
I _was_ going to replace just the air pump, but my BMW technician buddy strongly suggested I replace the check valve as well, otherwise the pump would fail again quite soon. 30,000 miles later, and the air pump is still doing fine.
[ BTW, the part numbers/prices are: [ o check valve, $94, BMW p/n: 11 72 1 744 255 [ o air pump, $268, BMW p/n: 11 72 1 432 907 [ [ Reference: http://www.realoem/com
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Where's the water vapor coming from?

It's actually a natural byproduct of combustion. I was very skeptical
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Good info. Thanks.
Leonard

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