Few month ago my Canon 17-85 lens started giving «Error 99» with my Canon 400D DSLR camera. Little googling, and I found the cause of this. Problem was in the diaphragm unit in the lens. Diaphragm unit connected to the lens motherboard with flatcable, which is damaged with time, when you use zoom ring. The only way out is to replace flatcable or diaphragm unit with flatcable assembly. Because now I live in Thailand, and I don’t have a copper, I ordered diaphragm unit assembly on EBay.
This is my lens. Beauty :)
