We have a 1998 528i that shows a DTC, I forget the #, but it points to the Secondary Air Pump. There is no power going to the pump. If I use an external 12V applied to the pump it runs. Does anyone know if the pump is supposed to run all the time? I didn't find any bad fuses, but I also didn't find any fuses labeled, Secondary Air Pump. Is it controlled by a relay?
There is a valve/switch installed down stream of the scondary air pump. It is vacuum operated. I followed the vacuum line to a switch mounted between intake runners 1 & 2. I'm guessing that when the switch is activaed it lets vacuum pass through to the valve/switch downstream of the secondary air pump. The plug that goes into the switch did not have power when I checked it. Does anyone know when this switch is supposed to be activated? ( it may be called the Back Pressure Valve) And what activates it? We do have vacuum to the switch.
There was info on the switch:
7 22341.00
12V 98T145
1 742 712
Pierburg
PA6 GF30
We are still trying to find out more about how this whole system works.
We are also trying to identify which relay and/or fuse controls the secondary air pump.
Any info would be appreciated however small it might be.
Thanks!

There is a fuse under the carpet, right front floor, and a relay under the hood. Fuse is most likely the problem BUT the pump may be going bad. Water likes to get in the pumps from a defective valve on the exhaust manifold.
You can check for power at the relay, battery voltage at the large red wire and key on voltage at the small red/white wire.

swap out that valve on the hose to the pump too- I didn't know about that and now I'm on my 3rd sec. air pump. :(

bimmerfixer knows his stuff!