On Sat, 28 Oct 2006 16:25:00 -0700, derek_mcquarrie wrote:

On mine ('99 328is E36 2-door) the vacuum hoses that actuate the valve
on the exhaust manifold had rotted, causing the valve to open partially
or not at all. The computer set the same codes you're
experiencing...  Replacing the hoses fixed the problem, and it's been
trouble free for about 18 months since. Cheap fix!

Good luck with yours...

1998 E36 M3
check engine light came on a few weeks ago

Autozone code reader found P1421 & P1423: BMW specific codes

A search of the net finds that these codes indicate low oxygen in both
exhaust manifolds. Nothing serious though - the oxygen is delivered by
the secondary air pump for about 100 seconds after a cold start - now I
know what that thing is that sounds like a vacuum cleaner.

The pump is actually fine and has no signs of corrosion which can be
caused by exhaust gases coming back through a defective non-return
valve on the manifold.

So I browsed around some more, and found that a relay in the main power
distribution box can be bad, giving these codes. Pulled it and
re-installed the same one, went to Autozone and had the codes reset.

Codes came back a few weeks later - pump still hums normally during a
cold start, so I know it's not a serious problem, but does anyone have
an idea what the problem is. Intermittently bad relay is my best guess.

Cheers