From another forum. Not sure how helpful it is.
The general problem is with the secondary air system check valves. There are two, one on the driver's side of the engine, and one behind the driver's side engine head.
Guess which one is the general problem one! Right, the difficult to reach one. I was happy last year to hear about the WD 40 trick. By spraying the WD into the system and running it a bit, it frees up the stuck valve and the code does not re-occur. If you do a search you will see a lot on this, even someone has dissected one.