Hi all,

First one I noticed was the rear, I've found the thread on here regarding the spoiler off job and checking the connector. I've done that and I appear to have continuity screen-side, but couldn't get 12v at the car-side connector. I've checked the fuse for the rear, and all fine. Presumably, somewhere there's a relay (as I hear the click) but this isn't in the glove box fuse compartment, where the actual fuse is, nor is it with the other fuses in the engine compartment. There's a relay in there for the front heated windscreen and 2 fuses (left and right?) but unless they share a part I'm not sure where else to look. Theres definitely a click from somewhere though.

The day after (as it was masked by the warm blowers) I noticed the front isn't working either. Fuse OK, relay OK. My main question is, do these 2 demisters share a common component, like a DCU (demist control unit) or something like that. Or, do I just happen to have 2 very similar systems that are completely separate but nonetheless, both broken.

Thanks

The glass de-icers are common at failing at the front.
Check the relay is clicking
Remove A pillar inside on one side and check for power on the 2 connectors.
And check glass resistance when off and disconnected

The rear relay is soldered into the fusebox.

So today's update, and now I'm more confused. Let's just say electronics aren't my strong point.

Front screen - removed a-pillar trims both sides, tested continuity on both sides of screen, whilst disconnected, all good. Tested ohms with multimeter setting on it's lowest setting and see 0.08-0.10 both sides. Tested voltage at the spade connectors on the supply side, 0 with the switch off and a stead 14+ volts when switched on, again both sides. But no demist actually happens when it's iced.

Rear screen - removed spoiler and tested voltage supply side to chassis ground, 14+ volts when switched on, 0 when off. Tested continuty on screen side, all good. 0.08-0.10 ohms. Plugged back together, no demist happens. Left for 20mins the other day and was still frozen solid, not even a hint of the element lines showing through. I even jabbed the point of the multimeter into the sheathing screen side once plugged in, and was getting voltage (around 10-11 but connection probably wasn't the cleanest as I'd pierced through the insulation).

Any suggestions?

0.08-0.10 ohms. sounds (is) unrealistic. Is this on the 200R setting ?
I would expect closer to 1 Ohm


You could turn the front screen on, with it connected. And try and read the voltage and ensure its still a good voltage
(when loaded with the screen connected)

I think it's ur earth connections the black wire at the bottom on both sides iv just had this on our new to us D3 exactly as you describe.

Here is my post re fault checking my sport passenger side doesn't work in the case of the sport the screen is open circuit passenger side.

I removed the connections on the D3 and cleaned them up and all good


1st proper frost of the year so used the heated screen function for the 1st time only to find the passenger side didn't defrost doh. Drivers side cleared in a couple of minutes.

So break out the multi metre first things to check are the under bonnet fuses 30 amp x2 one for each side. Yep all good relay works easy check is to remove and refit it you should hear and feel it click.

Next is to pull off the internal A pillar covers the are x2 connection on each side for the screen heater elements top one has purple wire that's the power in quick check with the dvm yep 14ish volts. Engine running heated screen function selected.

Next the bottom connector it's got a black wire that's the ground you don't get any volt reading here you need to test for ground at the connector, make sure all the cars power is off no ignition on. Turn the dvm to continuity you can use the the heads of the bolts on the inside of the A pillar for a ground connection for 1 lead of the dvm the other lead to the black connector......zero ohms is what your after.

Well all those checks seem to suggest the cars electrics are working fine the final check is to unplug the screen element connectors from the x2 plugs and test the screen for continuity these are the ribbon like connector.

You should get 1 ohm resistance........ Censored iv got 53.2 ohms that's way to high conclusion is the heated screen element on the passenger side is open circuit.

The only fix for this is a new screen as its a function that's hardly used I think this will be left.

Double trouble the new to us V8 D3 ulez cars heated screen also failed to operate same tests performed fault found to be poor connection at the earth side of the screen both left and right. Quick clean up and all fixed.

Result.....partly.