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
Where's the water vapor coming from?
It's actually a natural byproduct of combustion. I was very skeptical
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