The ongoing story of the cooling control unit, Well it is finally fixed and working perfectly as it should.
This one had me going for a while, first it was not even wired up properly, next the sensors were broken, missing and not wired.
Then electronic components had failed in the unit.
That brings us to today;
After i had actually fixed the electronic side of the unit i reinstalled it in the truck only to find it still didn't work.
It was working perfectly on the bench, all the truck wiring and sensors and valves were correct and working.
So this didn't make any sense at all, I decided the best option was to connect the unit to the truck whilst it was open and recheck everything at the circuit board itself.
Here it is connected to the truck ready for testing.
I discovered as i had suspected that all the sensors were correct, However when i checked the output to the oil valve that operates the fan, i found it to be shorted to ground.
I disconnected the multipin connector from the box and metered it there, No short. On further investigation i discovered that inside the control box there was another wire connected to the valve output as well, when i removed it the short was gone !
According to the truck wiring diagram there should be no connection to that pin. I can only assume that at some point someone had connected the wire on that pin to earth somewhere in the loom, thus shorting the oil valve output and causing the fault.
Here is the offending wire now disconnected and insulated.