Nissan Patrol K160 Pre-heat System

I'm having problems with my pre-heating system for my Nissan Patrol K160 3.2TD!
The Eektronik is no longer responding to the engine temperature, and regardless of whether the engine is cold or hot, it always has the same pre-heating time! I thought it was working through the coolant temperature sensor, but that one is fine! Is there another sensor? Does anyone have any other ideas? Are there perhaps any schematics?