2006-07-23 
Front (of engine) sensors DC resistance 725 ohm.
All are well-insulated (>200 Mohm from screen and battery earth.

The DC resistance rises as the sensors get warmer, up to about 1200 ohm when the fans cut in. (Strangely some of the fault-finding procedures say to replace the sensor if the resistance exceeds 1000 ohms.  Clearly the authors have only checked them on a cold engine.  The distributor (120 deg) sensor stays warm for ages after stopping,