Thanks for the post, it may be helping me understand the problem a little better. The photos Gary posted are of the the PSE "control module." I believe the PSE pump resides directly above it in the compartment accessible from the trunk. In my case, the pump is manufactured by Hoerbiger in Germany and bears several numbers: A170 800 00300, 180221, and HB92907-100.

I believe the PSE "pump" in my car works fine. However, I can easily believe that the PSE "control module" is the cause of the problem, which seems to be a communication problem between the pump and the alarm system. It looks as though the "control module" would be less expensive and easier to replace than the "pump."

Does anyone know of a good source for a replacement PSE control module. Alternatively, if one does not care about having the use of the alarm, is there any reason why the other sysetms connected to the PSE pump will not operate correctly if the alarm horn is disconnected?