E39 528i secondary air pump -- need help

Need help troubleshooting a problem I've been having with my E39. The secondary air pump, the diverter valve w/gasket were replaced less
than 6 months ago. The #117 MIDI 50Amp fuse was blown and replaced as well. Last March noticed a Hoover sound coming out of the SAP area for about 10 min. After that incident the SAP stopped working and I got the P1423 code. I thought that the fuse blew again and because itís such a pain in the neck to replace it I didnít do anything about until last week. Last weekend I opened up the fuse panel under the passenger seat to check the fuse and it checked out ok. Next, removed the pump and it was dead. It smelled like it was burned too. From the Bentley diagram it appears that the ECU controls the SAP circuit through a relay in the ECU compartment. The pump should be on for 1-2 min when ambient temp drops below 51F. What would cause the pump operate for more than 10 min and, as result, burn it? Sticky relay contacts? Bad ECU? Leaky vacuum hose somewhere? Any comments would be appreciated.
- Vadim
US Spec '99 528i 5 speed
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