Couple things to add:
1. Do not do anything if you get the code once, it could be a bad tank of gas, impurities whatever. Fill up again and half way through take it to a autoparts place and have them pull the codes again (most will for free). If it remains, do it again at another tank. Give it a few tanks before considering anything.
2. Once you are certain that its bad you have a few options:
Get it repaired
Pros: It put your engine back in to correct working order
Cons: EXPENSIVE repair, quotes have been in the $750-$1500 range
Pros: You don't have to do anything
Cons: Your engine may not perform at its peak and you may be costing yourself some gas milage (how much varies)
Pros: Moves it to a much more easily accessible spot, cost is much cheaper then replacement ($200 using OEM parts), your engine has knock protection again
Cons: Not in the factory location, not as accurate.
Bypass mod (not recommended for SC engines)
Pros: Regains timing and milage lost from bad sensor, very cheap
Cons: You now no longer have ANY knock prevention, could lead to engine damage but unlikely.