Even with the fan removed, it still takes alot of manual deterity to remove and clean those connectors. It's done by unplugging/plugging the connector about 10Xs, then apply dielectric grease and hope for the best.

If it's already been done yet still not fixed, the next least costly step is to replace the knock sensors (both) with the new type which is one part directly hardwired to both sensors, done to eliminate the possible connection problem. Once that's done and IF the code(s) still appears for a knock sensor, you'll be looking for a replacement ECU. I've seen that occur at least 3Xs so far and there's no viable tests to check the ECU for that intermittant fault code problem ahead of time. You must just do it by process of elimination.