secondary air flow fault code on audi a4 2007
 

Hi please help. I have a a4 2007 and im getting the code for secondary air flow fault, could this be a fuse if so where is the ECU box? I had this warning light turned off by the AA, the engineer said if it comes on again take to garage but after reading a little turns out it could be s fuse so yes I just need to know where the ECU box is situated so I can have a look. Please help :)