Its not inaccessible, its just hidden behind a heap of other stuff. Diagnose the issue, the majority of these are either wiring issues or a mechanical issue triggering the knock sensor. Rare for the sensor to fail.It has not been repaired because it is inaccessible. Usually the 're-detection' takes a few drive cycles to occur but not this time. It appears within a few seconds of starting the engine and reappears on the code readers even after being erased. I need to find someone who has experienced this same issue and has resolved it. Surely this can't be a 'first time ever' event.