Knock sensor failure
 

My MY00 UK Turbo PPP has twice, in the last month, shown a CEL. It comes on when the engine is started and stays on for about 60 seconds, then goes out. First time the engine was cold and second time it was still warmish (2 hours off). Because the engine was not up to operating temp I wasn't giving it much throttle. These are the only tomes it has happened. I use BP Ultimate fuel. (No other option)

When I checked the fault code it showed 22 i.e. Knock sensor. The car appears to run fine though.

Is it possible to get a knock sensor fault from it detecting knock or would it just retard the ignition as per normal running?

When the light goes out does it mean the fault has cleared and all is working fine again?

If the sensor is faulty how mush is a new one an where is it on the engine?

Thanks