Webasto FBH - Help me diagnose failure?

Early Discovery 3s used to use the W Bus when the first edition of the stereo software had a timer built in. However the FBH timer was deleted from the software at the end of 2005. From this point onwards the W Bus wiring was not fitted from the factory. At this point, early D3s had the timer removed by a later SW release, although the wiring was left in place as it was part of the harness.
The later optional cold climate timer, (actually the Webasto 1533 Oval timer) was connected to the FBH with a W Bus harness.
I had a custom remote for my D3 which also fired the FBH using the W Bus.

Ooo very interesting. I finally managed to summon the energy to fit the new dosing pump.

I noticed a very corroded black wire near the dosing pump mountings - anyone know what this is for? It didn't affect the dosing pump test.


The photo abouve shows the plastic carrier for the dosing pump, that slides into the other plastic carrier with the engine pump? in it.

A quick test on vehicle - all seems ok.


Back together with new clips before the liner was re-fitted. Quite a bit of rust in this area, a job for the summer maybe to wire brush and paint the rear chassis bits.

@landyhaze. The black wire ties the fuel pump to the chassis electrically, presumably for safety. This wire does become detached over time. I need to get on and sort out my FBH which hasn't worked since I got the vehicle last month.

Today I have mostly been removing the wheel arch lining to get to the FBH. Much dremmeling of rusty screw heads was done. Once I got to the FBH, I discovered the wires I got from my junk box were too fat to fit the FBH 6-pin connector (they were 2.5mm OD and all the wires on the landy seem to be 1.3mm (actually inside they are 12x0.2mm strands). I also couldn't reach the fuel feed to the FBH with the front bumper on, so I was not able to purge the fuel line either. So I gave up and dremmeled the battery bolt instead. New wires are on order from a popular auction website. I chose green and purple. Green since it matches the colour of the 'Analogue' output on the T91 harness I have, and purple for the fan drive, becuase I could.

Wow, has it been that long since I stopped playing with the FBH.? Well, after a very cold day, I thought it a bit silly to have a working FBH in the shed, so I thought I would try to replace the dead one on my 2004 Facelift TD4. I found the old gaskets to seal the PCB in, but they are all swelled up - and I can't find a supplier for them. I guess I might just use a shed load of silicone sealant, and hope I donlt have to open it up again...?

Could you not just make a neat cut and shorten the gasket ? and then seal at the joint, I have to reinstate two PCB boards today from the two spare FBH I have for the R40 MGZT diesels these have just come back from French Mike after being sorted out.

Arctic2 said:

Could you not just make a neat cut and shorten the gasket ? and then seal at the joint, I have to reinstate two PCB boards today from the two spare FBH I have for the R40 MGZT diesels these have just come back from French Mike after being sorted out.

Click to expand...

What's the white mushroom thing all about Arctic?

Hi Arctic2,
It just so happens I attacked the gaskets with a scalpel and stuck them back together. One with cycle glue, and the other with super-glue.I wonder which will last the best?
It took me 4 hours to swap over the dead FBH for my repaired unit.I mostly spent time trying to remove the two hidden rusted screws that hold the front bumper onto the wings. I managed to do a test with the new FBH in , Fuse 5 replaced, checked the temperature sensor was closed for such a cold day. It took a few minutes for the FBH to start up - probably as I didn't bleed the fuel line. The result was , with the engine idling the FBH ran for 29 minutes before cutting off, with the temperature guage reading just to the left of straight up.ISTR trying this test with the FBH not working on a similarly cold day, and it didn't quite manage to get the temperature guage to the 1/4 way mark after 90 minutees, when I gave up. Next job is to fit the remote control...

Nodge68, The white mushroom things are silicone, they put it on PCBs that are subject to extreme vibration. It stops the big blue bits from shaking themselves off.

Nodge68 said:

What's the white mushroom thing all about Arctic?

Click to expand...

landyhaze said:

Nodge68, The white mushroom things are silicone, they put it on PCBs that are subject to extreme vibration. It stops the big blue bits from shaking themselves off.

Click to expand...

Hi Nodge landyhaze is correct we have found out that this silicone attacks dieode's on the boards in that area and then needs repairing, which is where French Mike comes in, he does most of ours on the R40 forum, I had some returned Friday and they have now been fitted to the FBH which come next week will be in the hands of new owners.

landyhaze said:

Nodge68, The white mushroom things are silicone, they put it on PCBs that are subject to extreme vibration. It stops the big blue bits from shaking themselves off.

Click to expand...

I'm assuming you are referring to the capacitors

Arctic2 said:

Hi Nodge landyhaze is correct we have found out that this silicone attacks dieode's on the boards in that area and then needs repairing, which is where French Mike comes in, he does most of ours on the R40 forum, I had some returned Friday and they have now been fitted to the FBH which come next week will be in the hands of new owners.

Click to expand...

Silicone shouldn't be anywhere near electronic circuits, unless it's dried in controlled conditions. It contains acetic acid with will attack copper quite badly, even when set. It's much better to use a hot melt clue. Or for more permanence, use an encapsulation compound.

I'm interested in seeing a faulty board.

Interesting - The PCBs are conformally coated with laquer before the white gunk is applied. I guess it is possible at the factory they use two part silicone rather than the self-curing RTV stuff with the vinegar in - learnt something new about the corrosion.

My triumph was short lived with my FBH - I went out this morning to start the Freelander (OAT 0.5 C) - the FBH kicked in, but gave up 5 minutes later. (the fan kept cycling) I kept the engine running for 40 minutes,but the temperature gauge was registering less than 1/8 of 'full'. I hooked up the laptop, and got the fault out - "Combusion Air Fan Interruption" . Great. So I likely have a thermal intermittent fault on the PCB I just repaired, and then to add insult to injury the engine put out smoke on acceleration for the first mile of my drive - not surprising as it had been idling for so long this morning and at the weekend. I have a spare FBH, with a different problem, so maybe some swapping [PCB] over at the weekend - is that possible without draining the coolant?

Have you checked the glow plug or cleaned the carbon out of the combustion chamber?
That would be my first check tbh. They are a dirty burning thing sometimes. Maybe the CO is set wrong, causing it to soot up.

I had it running just fine on Saturday - it fired up first time after 9 months in the shed - no smoke, just worked perfectly for 29 minutes...

Hi Nodge /Landyhaze
You should be able to change over the PCB board without removing any pipe work, that is if you have access to the top of the FBH I have not yet looked at mine so am not sure but I must get round to it, I also added a link previous which is here below which may help,
http://www.the75andztclub.co.uk/forum/showthread.php?p=877768#post877768

This link is also from French Mike for those whom are not able to mend/repair their PC boards such as myself you can contact him and send your PCB which he will check and repair for you, well worth it in my opinion.
http://www.the75andztclub.co.uk/forum/showthread.php?t=53896

I think I can get the PCB off by 'just' removing the passenger side front wheel arch liner. Can you PM me french Mike's contact details - I may just send one of my spare PCBs to him - it would be nice to have at least one thing in the equation to be known & working.

Arctic2 said:

Hi Nodge /Landyhaze
You should be able to change over the PCB board without removing any pipe work, that is if you have access to the top of the FBH I have not yet looked at mine so am not sure but I must get round to it, I also added a link previous which is here below which may help,
http://www.the75andztclub.co.uk/forum/showthread.php?p=877768#post877768

This link is also from French Mike for those whom are not able to mend/repair their PC boards such as myself you can contact him and send your PCB which he will check and repair for you, well worth it in my opinion.
http://www.the75andztclub.co.uk/forum/showthread.php?t=53896

Click to expand...

That's a very good write up. I now see the problem is a simple SMD resistor failing. That's worth knowing. I can easily change that myself.
I have thought about sorting out a data connection to the FBH. I was going to do this when I had my D3. However I bought a diagnostic which could test the FBH in that anyway, so never bothered.
I'll have to sort something in the future though.

Nodge68 said:

That's a very good write up. I now see the problem is a simple SMD resistor failing. That's worth knowing. I can easily change that myself.
I have thought about sorting out a data connection to the FBH. I was going to do this when I had my D3. However I bought a diagnostic which could test the FBH in that anyway, so never bothered.
I'll have to sort something in the future though.

Click to expand...

You can test that 4.7K resistor yourself with a DMM

landyhaze said:

I think I can get the PCB off by 'just' removing the passenger side front wheel arch liner. Can you PM me french Mike's contact details - I may just send one of my spare PCBs to him - it would be nice to have at least one thing in the equation to be known & working.

Click to expand...

No problem I will send it over now, say Arctic referred you.

Thanks Arctic - Hazel