Help with the heater rear screen.

[Nathan Buffery]

Morning all. I am 99.9% through updating my mk 3 focus heater controls to the facelift controls. I wanted to change them after fitting the sync 2 and I picked up a facelift centre console. As I said I'm 99.9% there and when I'm happy with it I would like to submit a guide. 

I've studied the wiring diagram for both cars (although both of them do not match what I have) for hours and after lots of trial and error, everything is working apart from the heater rear screen. 

On the older unit there was only 4 wires in the terminal (it was a separate switch). Brown = illumination, Black = earth, Brown/Green = HRS light and Green/Orange which I can think is the switch. I think, after reading the forums, that it works on resistance rather than a live in and live out.

On the new unit I am using pin 14 Green/Orange and 15 Brown Green on the Blue bottom plug. But can't seem to get it to come on. Swapped the wires, tried 12 and 13, checked the fuse but nothing seems to work. To make matters worse, I think I read somewhere that the engine has to be running for it to come on. 

Any ideas would be greatly appreciated. 

[Nathan Buffery]

Anyone???

[Nathan Buffery]

Ok....not getting any response.

Lets try another tack....

Is there anything that stops the heater rear screen coming on? Maybe a humidity sensor or outside temperature? Also, I have used Forscan and Focccus software, so could I have somehow turned it off?

Should of said at the start, its a Mk3 focus edge estate 2013. I've updated to sync 2.

[FatHead1979]

On 9/11/2019 at 3:02 PM, Nathan Buffery said:

Ok....not getting any response.

Lets try another tack....

Is there anything that stops the heater rear screen coming on? Maybe a humidity sensor or outside temperature? Also, I have used Forscan and Focccus software, so could I have somehow turned it off?

Should of said at the start, its a Mk3 focus edge estate 2013. I've updated to sync 2.

I don't think there's any sort of temperature/humidity criteria that might block manual activation, if the engine is running and you've pressed the button it should power on.  (I don't know for definite that the engine needs to be running but I know it does for the heated (front) windscreen, which admittedly does draw more current than the rear heated window but if it's not working with the engine running then I'd say something is definitely wrong somewhere i.e. maybe config via Foccus/Forscan or a physical issue with the switch/wiring etc.

 

In Forscan can you see a PID for the rear heated window?  If there is then you'll at least be able to see if things are working as far as the switch and wiring through to the ECU.  If all that is working then you can safely assume the fault is somewhere after the ECU/BCM i.e. the actual wiring loom that runs from the front to the rear of the car (or it's connection to the rear window etc).

[Nathan Buffery]

Thanks for replying Damian. I was beginning to think I was the only one seeing my posts!!! 

I'm away at the moment (I work at sea month on month off) so can't run any test until I get back. I was thinking of putting wiring the old switch back in, just to see if it works. It's so frustrating as everything thing else is working. 

[Nathan Buffery]

On 9/18/2019 at 1:48 PM, 1979Damian said:

In Forscan can you see a PID for the rear heated window?  If there is then you'll at least be able to see if things are working as far as the switch and wiring through to the ECU.  If all that is working then you can safely assume the fault is somewhere after the ECU/BCM i.e. the actual wiring loom that runs from the front to the rear of the car (or it's connection to the rear window etc)

Ok, I'm back on this now. I stripped it all down and rewired the old switch. Its also not working, the little light is coming on when I press the switch, but not staying on. 

Forgive my ignorance, but are you saying that I can see if it's working, or at least see if there is a command for it to switch on, in Forscan?