There are two knock sensors. located in between the cylinder banks.
You can see the two black cables going of them.
To replace them the heads have to come off.
There is a water pipe going above them:
and with the heads on, you will not be able to access them:
Sensors should be about 50 EUR each, but the job is basically an engine rebuilt.
The sensor you mention, under the air intake hose, on the rear cylinder bank, close to throttle body that is cam position sensor.
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