Originally Posted by e39_touring

Ok, no mini maf on that system. Basically, the air pump operates at startup, and the ecm looks for the added air to affect o2 values. If it doesn't see the change, it throws the code.

The air pump comes on at cold start and should produce a brisk breeze out of the hose if you disconnect it. To test the valve, apply vacuum to the vacuum line and blow through the big hose to the valve. If you can't, the diaphragm is probably holed.