If the electric fan runs when the engine is not hot and the A/C is not on; it is almost certain that you have a CTS in
the lower radiator hose, where you should have a fan thermal switch.
You need to get the right parts in the right places, and then diagnose for any remaining issues.
The garage replaced the lower temp sensor. This fixed the Low temp reading on the temp gauge because they didn't change anything else. that was back in Jan/Feb. I was getting this error code - 17664/P1256 - Ross-Tech Wiki
That problem went away as soon as it was replaced so that lower sensor must give some form of feedback also.
The bottom one was working fine since replacement for 7 months so its unlikely an issue. Also garage fitted genuine replacement part there.
The Engine CTS was replaced a few days ago after starting to get over heat issues. So the upper ones just been replaced so then it goes back to thermostat/water pump.
The only thing the Fan Thermal Switch (front of engine) can do is switch the fan on low or high, depending on the coolant temp leaving the radiator.
It can not affect performance or this code 17664/P1256 - Ross-Tech Wiki
Note: The electric fan can work under certain conditions (such as with the A/C on) with the Fan Thermal Switch completely disconnected/removed.
You had this code in January 17664/P1256 - Ross-Tech Wiki, do you still have it or any other codes ?
This code can only be caused by a faulty CTS (rear of engine) or its wiring/connectors.
The new CTS could be faulty, but more likely you have faulty wiring.
You need to establish that you have the correct parts in the right places and that they are working properly, then start diagnosing.
You had this code in January 17664/P1256 - Ross-Tech Wiki, do you still have it or any other codes ? This code can only be caused by a faulty CTS (rear of engine) or its wiring/connectors.
The new CTS could be faulty, but more likely you have faulty wiring.
There are no codes currently on the car, those two went, I believe they were originally to do with the Inter-cooler issue. Causes were Lost of turbo/Power/Fuel efficiency/power all related. So the N75/Turbo were flagging up also. Once this was replaced all codes went.
The one code 17664/P1256 (Not codes) that I referred to, was as I stated caused by a fault in the CTS circuit.
I like to spend some time trying to help people, but if you just want to incorrectly dispute everything I say, I am not interested.
The electric fan should run at low speed when the engine and A/C are running; and at high speed
when the coolant returning from the radiator is above a certain temp. (about 100 Deg C)
Maybe a faulty WP, or the thermostat not installed correctly causing jamming. (could be in backwards, a few fools have done this)
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