Fuse 12 Fail - rear window (but it hasn't)

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NikTheGeek

NikTheGeek

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Hi, I was intermittently getting the message "Fuse 12 Fail - Rear Window Demister". Fuse 12 hasn't failed. I can hear the relay clicking away under the bonnet so I've replaced relay 4 and 5 (as I didn't know which one it should be) and still get the same message. I've checked fuse 30 and 32 (I think it was) under the bonnet too and they are all ok.

Any ideas?

tnx

Nik
 
Saint.V8 said:
The relay may click, but does the heater element actually work??
Click to expand...

No it doesn't work. When I meant the relay clicks, it doesn't sound right. It clicks off and on quickly a few times then goes silent. But I've replaced it and the new one does the same...
 
NikTheGeek said:
Narrow it down! :) What about the fuse box? Which one? Under seat or under bonnet? Lose wire? No other problems at all.

It was intermittent, but now it constantly doesn't work...

Nik
Click to expand...

Under bonnet fuse box is a common failure item, it's the only one with relays in it so didn't think it needed narrowing down.
 
Datatek said:
Under bonnet fuse box is a common failure item, it's the only one with relays in it so didn't think it needed narrowing down.
Click to expand...

No, sorry, narrow the fault down. I know there is a fusebox issue with burn outs, particularly on relay 7. But the rear demister is relay 4 or 5. I'll check for burn anyway. I was wondering if you thought it was a lose wire, dry solder joint, burning. And I didn't know if the under seat one was also subject to burning issues.

Is there a voltage overload relay on these? Something that turns the rear demister off when it detects a voltage drop? I've heard they can fail causing the rear screen to click on then off straight away.
 
NikTheGeek said:
No, sorry, narrow the fault down. I know there is a fusebox issue with burn outs, particularly on relay 7. But the rear demister is relay 4 or 5. I'll check for burn anyway. I was wondering if you thought it was a lose wire, dry solder joint, burning. And I didn't know if the under seat one was also subject to burning issues.

Is there a voltage overload relay on these? Something that turns the rear demister off when it detects a voltage drop? I've heard they can fail causing the rear screen to click on then off straight away.
Click to expand...
Not that I'm aware of.
It's not just around relay 7 that failures occur. It can be the connections underneath to the loom, the solder joints in the fuse pcb assemblies, track corrosion etc.
Under seat fuse box not a problem normally.
 
Am I reading this wrong, but looking at my schematics in RAVE the Heated rear Screen doesn't have a seperate relay - the relay sits in the BeCM....as attached

Am I losing the plot??
 

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Saint.V8 said:
Nope not going mad - relays 4 and 5 are for the Front Screen...Rear is BeCM controlled....
Click to expand...

Ok... that was a waste of a few quid and a trip to Halfords then! :)

Right, in that case, the BECM is the long square aluminum box under the drivers seat with all the connectors to it? Would the relay be internal to it? Or fastened on the outside? It really does sound like a failed relay because of the clicking, but obviously, it would help if I changed the right one! :)

Nik
 
NikTheGeek said:
Ok... that was a waste of a few quid and a trip to Halfords then! :)

Right, in that case, the BECM is the long square aluminum box under the drivers seat with all the connectors to it? Would the relay be internal to it? Or fastened on the outside? It really does sound like a failed relay because of the clicking, but obviously, it would help if I changed the right one! :)

Nik
Click to expand...

Looking at the schematic, Relay 11 is internal to the BECM. So I might have to admit defeat at this point....
 
NikTheGeek said:
Ok... that was a waste of a few quid and a trip to Halfords then! :)

Right, in that case, the BECM is the long square aluminum box under the drivers seat with all the connectors to it? Would the relay be internal to it? Or fastened on the outside? It really does sound like a failed relay because of the clicking, but obviously, it would help if I changed the right one! :)

Nik
Click to expand...
IIRC they are internal and PCB mounted....will see if I can find a pic

And yes the BeCM is the large Ali thing under the drivers seat....
 
Thanks. I'll start by checking all the connections are tight and not damp or anything. If that's all ok, I'll leave it until I have plenty of time...
 
Put a meter across the output to the rear screen from the BECM and check the voltage.
a lot of relays of the type in the BECM have removable lids, once open, it's possible to clean and adjust the contact with a bit of care. I'll have a look tomorrow if it will help. The relays are not too difficult to replace but you do need a good fine point soldering iron and a solder sucker. Be very careful of static electricity on your hands when handling the BECM innards.
I didn't know the rear screen was controlled from the BECM, thought it was like the front screen. Another bit of overcomplicated design.
 
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