[MrWani]

Hi all, first post so hopefully posting in the right place.

I purchased my 2011 E92 330i about a month ago from a mate with a known problem with the heated rear screen. I've tried a load of things but not got to the bottom of it:

- Button on dash lights 
- Replaced the IBS based on other forum posts 
- Replaced the battery (At the stealers so hoping they registered it correctly) 
- Checked the fuse (ok) and showing 12v when dash button pressed. 
- Doesn't appear to be a replaceable relay on this model. 

https://www.newtis.info/tisv2/a/en/e...indow/haeyxn6+

 
- Reads 12v on the actual bars. 

Still I get no clearing of the rear screen. I also get an error code 'A6C8 Heated rear window relay' which I've cleared but keeps returning. 

My assumption since I get 12v in the bars themselves that this must be the earth or a fault in the earth connection on the screen. Problem is I've no idea where to look to find the wiring and don't really want to start ripping off panels without narrowing it down.

Any help much appreciated.

[bfleming]

On the wiring diagram you link, there's a relay shown, K13 right at the top. There are a few variants of the E90 fuse box (having wired my heated seats last week I know all about it!) but in general when you look in at the fuse box, the relays concerned are on the left hand side. There's more than one. You should hear an audible click when you turn the heated rear window on (I do, my car is a 04/2010 build).
Failing that, the 'lockout circuit for rear window defogger' must be the culprit. Isn't this the antennae module located around the c-pillar on the passenger side? Maybe?

[MrWani]

Originally Posted by bfleming

On the wiring diagram you link, there's a relay shown, K13 right at the top. There are a few variants of the E90 fuse box (having wired my heated seats last week I know all about it!) but in general when you look in at the fuse box, the relays concerned are on the left hand side. There's more than one. You should hear an audible click when you turn the heated rear window on (I do, my car is a 04/2010 build).
Failing that, the 'lockout circuit for rear window defogger' must be the culprit. Isn't this the antennae module located around the c-pillar on the passenger side? Maybe?

thanks bfleming,

the k13 relay is built into the junction box. A YouTube video on another thread explained that the solid line refers to a built in component Vs dashed lines which are replaceable (fuses etc).
I listened for the relay this morning and can definitely hear a click.

I'll try to uncover the c pillar this weekend thanks for that suggestion. Will it make a difference that mine is right hand drive? Still passenger side ?

[bfleming]

Just reading back through this thread, you don't say if you've tested the earth. That's what I'd test next. You'll need to take the c-pillar trims off on both sides, that'll give you free access to the wiring to the rear window on both sides.

Borrowed from Pelican Parts:

Lever out fastener cover:


Undo Torx T20 bolt:


Pull C-pillar trim panel up and away from C-pillar while detaching it from the window seal:

[MrWani]

Originally Posted by bfleming

Just reading back through this thread, you don't say if you've tested the earth. That's what I'd test next. You'll need to take the c-pillar trims off on both sides, that'll give you free access to the wiring to the rear window on both sides.

Borrowed from Pelican Parts:

Lever out fastener cover:


Undo Torx T20 bolt:


Pull C-pillar trim panel up and away from C-pillar while detaching it from the window seal:

That's basically where I'd got to but didn't know where to find the wiring. it could have been on the rear shelf, boot or c pillars as you've pointed out.

I'll have a go this weekend. thanks for the pics would never have guessed to look under the airbag symbol.

[charliewaqs]

I'm pretty sure there is a relay behind one of the C pillars. I can check ISTA for you if you want and post up the diagram.

[rasa bmw]

you deffo confirmed fuse is ok ?,,when i got mine i realised the rear heater wasnt working,,so i got a diagram of fuses and looked ok,,but no it wasnt,,the rear window fuse was in the wrong slot,,i think it was in the one next to it,,swapped it over and hey presto

[MrWani]

Originally Posted by charliewaqs

I'm pretty sure there is a relay behind one of the C pillars. I can check ISTA for you if you want and post up the diagram.

That sounds very promising... In the back of my mind I've always been aware of the error code for the relay but couldn't find one mentioned or any of the diagrams I've seen. Not sure what ista is but if it can be checked that would be fantastic. I'll have a look behind the c pillars at the weekend either way.

[MrWani]

Originally Posted by rasa bmw

you deffo confirmed fuse is ok ?,,when i got mine i realised the rear heater wasnt working,,so i got a diagram of fuses and looked ok,,but no it wasnt,,the rear window fuse was in the wrong slot,,i think it was in the one next to it,,swapped it over and hey presto

yeah pretty confident. I've had the fuse diagram and it's exactly where it should be. I can also see 12v come on and off through that fuse when I toggle the button. thanks though all advice and thoughts appreciated until I get to the bottom of this.

[bfleming]

Originally Posted by MrWani

That's basically where I'd got to but didn't know where to find the wiring. it could have been on the rear shelf, boot or c pillars as you've pointed out.

I'll have a go this weekend. thanks for the pics would never have guessed to look under the airbag symbol.

The online info is vague, but here's what you could expect to find:

[MrWani]

Originally Posted by bfleming

The online info is vague, but here's what you could expect to find:

ouch... hopefully not going that far but useful pic. That grey box (looks like a laptop power pack in the pic) looks interesting although my thought was it will be the driver (and battery) side pillar due to the fact that I get voltage across the bars. that's assuming the wiring comes from the junction box to the rear down the passenger side and then across and finally earthed. I'll post pics of what I find.

[bfleming]

Originally Posted by MrWani

ouch... hopefully not going that far but useful pic. That grey box (looks like a laptop power pack in the pic) looks interesting although my thought was it will be the driver (and battery) side pillar due to the fact that I get voltage across the bars. that's assuming the wiring comes from the junction box to the rear down the passenger side and then across and finally earthed. I'll post pics of what I find.

Indeed, if you go as far as the picture shows, you're in trouble. But you can see the antenna pack on the lower pillar, and you'll be able to see clearly the heated rear window wiring when you remove the trim on both sides.
You will pick up 12V either side of the screen if the earth is bad as the screen elements provide no resistance, i.e. the current doesn't flow.

[charliewaqs]

Originally Posted by MrWani

That sounds very promising... In the back of my mind I've always been aware of the error code for the relay but couldn't find one mentioned or any of the diagrams I've seen. Not sure what ista is but if it can be checked that would be fantastic. I'll have a look behind the c pillars at the weekend either way.

It's BMW's official diagnostic software mate. I was looking at this recently as my cousin has the same problem as you in his E92 335i.

Will post up an image tonight hopefully.

[charliewaqs]

Lockout Circuit Positive on one side and Ground on the other. Both of them are connected to the rear defogger (E9 label in pics). Check all connections pal.

[MrWani]

Originally Posted by charliewaqs

Lockout Circuit Positive on one side and Ground on the other. Both of them are connected to the rear defogger (E9 label in pics). Check all connections pal.

That's awesome mate, know exactly what I'm looking for now. Hopefully just a dodgy connection in there somewhere.

[charliewaqs]

No problem. Make sure you update us on outcome!

[MrWani]

Found the problem

[MrWani]

Removing the C pillar covers only revealed the top of the wiring boxes. So went onto removing the rear parcel shelf.

[MrWani]

Discovered the passenger side had the badly shorted connection.

Thank you guys for all your help.

Just need to source the replacement parts... any recommendations on where best to go?

[charliewaqs]

If you want used should be on eBay for tenner max. I don’t see New being too expensive so give bmw parts a call too?

[MrWani]

Originally Posted by charliewaqs

If you want used should be on eBay for tenner max. I donÂ’t see New being too expensive so give bmw parts a call too?

Yeah found one cheap on eBay with the connector. Tried to go round the scrap dealers also but not one bothers to open at the weekend. BMW weren't too bad £38 but none in stock so have to wait. So glad I've got to the bottom of it, and thanks again for all your help.

[charliewaqs]

No problem. Where does that damaged blue connector run to? Just in case on my cousins car it’s the exact same failure as yours.