Knock sensor

Please please help. I drive an Opel America 2004, z16xe engine. My service light came on and I lost power. I took it for a service and afterwards I still had the same problem. Was send for a diagnostic test and it showed knock sensor. Had it replaced with genuine Delphi sensor and for 3 months I was singing praises. After 3 months, same problem again and I had it replaced 4 times already and no joy. Mechanic just tells me if it showes sensor then it must be sensor. I am not a mechanic, but I am sure something else must be faulty. Any advice? Please help me