Air pump problems!

Hi,
I bought my 2001 Sonoma 4x4 in March of this year. The dealer told me he had changed the air pump before selling it to me. The day I have gone with the truck, the check engine light came on so I went back to the dealer. He had it checked back and the code was «Secondary Air Injection System», the air pump. The mechanic checked out all the fuses and relays but everything was fine. He told me that the pump was defective and that he will have to replace it(on warranty). About two weeks ago, the check engine light came on again, the same code. I went to my local garage and we found out that a 30A fuse was blown out in the air pump circuit. We thought maybe the pump had frozen and made the fuse blow. So they replaced the fuse, erase the code and everything was fine for about 2 weeks until today; the check engine light came on again so before going to my mechanic, I checked this 30A fuse and it was blown again. So before I change the fuse or replace the air pump(bit expensive for anti-pollution), I would like to know if somebody had similar problems and if there are known issues with this model, if somebody know why I have so much problems with this air pump?

Thanks