Viano 2008 Rear Window Demister Not Working

[andy_g]

Hi all, I've got a 2008 Viano with lift up rear door. The rear window demister stopped working a while ago - now when I press the button the orange light comes on for a couple of seconds and the flashes 5 times then goes off. I took the trim off the inside of the door and found that the wire to the left side of the demister had rubbed on a sharp edge of the door and probably short circuited to it. I've repaired the wire but haven't got the Demister working again. The demister element resistance measures about 1ohm with the wires disconnected so I think that's probably ok. With the wires disconnected from both sides of the demister, and the demister turned off, I measured about 6.5v on the right wire and 0v on the left one (with the demister turned off). When I connect both wires to the element I measure 0v on both sides and no change when I press the button to turn it on. The no. 12 fuse in the main panel of the fuse box under the bonnet is good which the manual says is for the heater rear window. With the fuse pulled, I measured 0v on both sides of the fuse socket. I've not been able to try measuring the voltage there when pressing the demister button.

It feels like maybe the short circuit has damaged some electronics but I don't know where to look next or what to try changing. Can anyone offer any advice as to what might be damaged?

The battery is new and in good condition and everything else is working as it should.

Thanks, Andy

 

[andy_g]

I also tried swapping the yellow relays in the main fuse box for the rear demister and rear wiper around but the wiper still worked and the demister didn't do it doesn't seem to be that.

 

[M80]

Is the relay energizing when you push the button? If not it 's likely the SAM.
Then with the cover off the relay.
Is there 12 volts at one side of the relay contact, fed from the fuse?
If all that's ok, then shorting the relay should give 12 volts at the heater, with one side disconnected. If not you've still a break in the wiring, 12v +ve, or the ground. Just need to sort out which.
Have you checked for a good ground?