P1619 - Map Cooling Thermostat Control Circuit Signal Low

Can anyone tell me what the DTC P1619 - "Map Cooling Thermostat Control Circuit Signal Low" means on my 2001 E46 330ci?
Also, can anyone tell me what could cause it?
It has been to the dealers twice and an independant once with this fault, but neither have acted on it.
Many thanks
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.