AO Gold Member
Join Date: May 2008
Location: United Kingdom
County: Perth and Kinross
Think it gets it from the ECU, which gets it from the sensor in the thermostat. When this is unplugged, you'd expect the fan to run all the time.
Check the plug's on ok, and the contacts are clean. It might need replaced (£12 or so). Not sure if its failure would bring on the engine management light or not though...
BTW, the temp gauge sender is in the same sensor (unless it's a very early 156), but is a different 'feed' than the one the ECU gets...