My 2001 Jaguar XJ8 Vanden Plas was left unused for most of the winter and when I got it running in the spring the CEL was on with codes P0327 and P0332 which indicates the knock sensors are bad.
Both knock sensors on this car have leads about 12" long that connect to a plug located adjacent to the thermostat. Coolant from the thermostat hoses or a cracked housing (common problem on XJ8s) can corrode the plug. I cleaned out both plugs with contact cleaner and removed both sensors and cleaned them off as well. The sensors are quite easy to remove on the XJ8. It is only necessary to pull off the plastic intake covers to access them.
The left back sensor was now fine, but the right bank sensor continued to throw the code. You can check if the sensor is the problem by inserting a 220kohm resistor in the plug. This should eliminate the sensor code and the car will be quite happy.
A replacement Jaguar sensor is approximately $200. I found this sensor on eBay for only $9.95:
HQRP Knock Sensor for Nissan Maxima 1995 1996 1997 1998 1999
It is identical physically to the Jaguar sensor, except instead of a 12" lead, it has a Bosch type connector. These connectors are common. I had a few in my parts bin that were wired to old harnesses. I cut the old sensor lead and spliced it to the Bosch connector.
Whether this sensor is as sensitive to engine knocks as the Jaguar one or not, I have no way of knowing. But I am sure it will detect knocking long before any engine damage ensues.