Avant rear screen demister

mpc

Registered User
I have noticed of late the demister on my rear screen takes longer to demist. All the bars work but seem to be very 'slow' activating.
I'm sure they never used to be like this.
Any ideas?
 

mpc

Registered User
Anyone?
Wonder if my battery could be an issue? Would it affect the demister if the battery was low on charge?
 

dts439

Registered User
Dodgy electrical connection to the element ?
 

dts439

Registered User
High current devices like the heated rear window can partially work if a connector gets contaminated, though more common on cars 30 years ago. Normally unplugging and plugging the connector a number of times + WD40 would fix it. Also could just be a bad earth depending on how its wired (e.g. like when you see cars with the wrong rear lights on when they brake...).
 

mpc

Registered User
High current devices like the heated rear window can partially work if a connector gets contaminated, though more common on cars 30 years ago. Normally unplugging and plugging the connector a number of times + WD40 would fix it. Also could just be a bad earth depending on how its wired (e.g. like when you see cars with the wrong rear lights on when they brake...).

Thanks for your reply, any idea on my avant where the connector is to the demister for me to try what you suggest?
 

richlean

Registered User
I am also interested in this. On Saturday my rear demist (A4 B8 Avant MY2010) stopped working altogether. I just did a VCDS scan and got:

02983 Connection between impedance converter 1 and window 011 - Open Circuit.

So I'm thinking that there's probably a connector which does both window heat and antenna.

I'll let you know if I make any more progress - planning to have a look this afternoon.
 

mpc

Registered User
I am also interested in this. On Saturday my rear demist (A4 B8 Avant MY2010) stopped working altogether. I just did a VCDS scan and got:

02983 Connection between impedance converter 1 and window 011 - Open Circuit.

So I'm thinking that there's probably a connector which does both window heat and antenna.

I'll let you know if I make any more progress - planning to have a look this afternoon.

Yeah keep me posted please....
 

richlean

Registered User
OK. The connection to the heating elements is at the top edge of the screen, slightly right of centre. You can prise back the interior trim with your hands or a flat plastic tool starting from the centre, and work outwards. That allows a good look at the solder connections. You could also check that the element isn't damaged between the solder joint and the rest of the window.

There are two connectors going into the long narrow box close to the soldered joints - anyone know what this is?

The coaxial one on the right can be removed by lifting the clip on it with a flat blade; the other one on the left with three wires pulls out towards you. I suppose these could be prime candidates for a dodgy connection.

There's a fuse (40A) and a relay for the window heat in the boot, on the right hand side behind the removable trim. I haven't worked out exactly which these are yet.
 

mpc

Registered User
OK. The connection to the heating elements is at the top edge of the screen, slightly right of centre. You can prise back the interior trim with your hands or a flat plastic tool starting from the centre, and work outwards. That allows a good look at the solder connections. You could also check that the element isn't damaged between the solder joint and the rest of the window.

There are two connectors going into the long narrow box close to the soldered joints - anyone know what this is?

The coaxial one on the right can be removed by lifting the clip on it with a flat blade; the other one on the left with three wires pulls out towards you. I suppose these could be prime candidates for a dodgy connection.

There's a fuse (40A) and a relay for the window heat in the boot, on the right hand side behind the removable trim. I haven't worked out exactly which these are yet.

Great thanks, If you can upload any pics that would be really helpful.
 

richlean

Registered User
OK - I'll try to add some pics of what I was talking about. First, the aerial amplifier and solder joints inside the trim at the top of the rear window:

40bf24fb851017b82605524259ae68e6.jpg


Here is the aerial amplifier. Apparently there are about six different types so don't assume that this part number is correct for you:

08c9ac3ed46148ce8a523e469a982b7a.jpg


Here is a diagram which shows the window heater circuit on the left:

0df5cc4678d90cae36b41d3acd1fd602.jpg


And here, I think, are the fuse and relay in the rear right side of the boot (camera facing rear of car).

f9b4b5a66c2619bbc5c727712a4508ca.jpg


Having said all that, I still haven't managed to make mine work!

Maybe yours really is down to a flat battery taking all the spare current.
 

ub7rm

Registered User
They do have an active power management system so if the car detects that available battery power is low the system will shut down system like the rear screen demister and heated seats etc to make sure there is available power for the essential systems. So it is feasible its a battery or charging issue. Though I would have thought it would be all or nothing, not reduced power.
 

mpc

Registered User
I'm the OP of this thread and i'm reviving this thread again as I still am having problems with my rear demister. Like I originally mentioned it takes an age for the window to demist - all the bars seem to work eventually. It never used to be like this going back a couple of years. I have replaced the car battery with a new one but that has made no difference. I have had a visual inspection of the connectors as the pics above but there didn't seem anything obvious.
With the colder weather coming I really would like to get this sorted and wondered if anyone else might have any other ideas please?
 

Gray S

Registered User
My 2015 model S4 Avant demister seems to take a while, but it has been very wet lately and the car not used very much
 

johnnythepie

Registered User
I take it that the inside of the screen is very clean...when i havent cleaned mine for a while it too takes a long time to demist
 

mpc

Registered User
I take it that the inside of the screen is very clean...when i havent cleaned mine for a while it too takes a long time to demist

Yes I do try to keep the inside of the glass clean. This week we had a very mild frost and normally this would start to melt within say 30secs of turning on the rear demist but it now can take up to 10 minutes!
 
Top