Webasto FBH - Help me diagnose failure?

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dampsox

Active Member
Posts
159
Started the journey to trying to figure out why my Webasto FBH/Aux Heater is no longer working. It was fine last Winter, they are a godsend.

The cabin 'instant-on' and Timer-Control Unit (LCD panel is glued onto the front ashtray) powers up, with LCD display apparently fine and the 'flame' symbol showing when I select 'instant on', but the cabin fans don't now come on under the Webasto control like they used to, and the Fuel Doser pump no longer ticks into life. No noises at all.

First, I checked all the wires into the rear of the Control-Unit LCD panel. One wire was chaffed through, but I fixed this.

Then, I did remove fuse-5 (20-Amp) a few times from the engine-bay Fuse-Box as per the Webasto user-instructions that came with the TD4 when I bought it, to 'Reset' the Webasto unit. But so far, no change.

Next up, I removed the Doser Fuel-Pump, it was externally deeply corroded and the mounts and fuel-hose clips had actually rotted away to nothing, it was hanging by its hoses. I replaced the fuel-hose clips with stainless ones and blew pressured air in each fuel line to blow back any obstructions in the fuel feed tubes. Then I intermittently tapped 12v DC across the Webasto Doser Pump (next to the rear offside wheel arch), and it ticked like it should and spat fuel with each tap of voltage.

I did find that 10.8 volts is always showing across the Doser Pump electrical connector, even with ignition off.

Is this normal? To have this voltage showing with keys out/ignition off?

Any help or suggestions so much appreciated, I am skint and need to fix this myself if I can. Just wonderin on the next step...
 
I found I had access to the removable exposed connectors of the Webasto heater unit just by removing the NSF wheel-arch liner. Not easy, as the metal fixing screws around the arch liner had rusted rock-solid.

19tdly.jpg


I now have access to the pins on the heater and the wiring connectors to run tests.

2vxon7m.jpg


While I was preparing for checks, I went behind and under the cabin fuse-box area to check the Webasto wiring installation, and found that one of the main wires powering the cabin fan was burning hot, and a slight wiggle actually made sparks! Holy smoke!

The Webasto installer or someone after this cut this wire that powers the cabin fan to allow the Webasto to power the cabin fan. It was a shoddy bit of electrical work - look how whoever did this, screwed down into the insulating plastic making a hot-spot. No wonder I had an intermittent fan! I also think I was lucky not to have a fire...

sopoyd.jpg


157hybs.jpg


Even if I can't fix the non-working Webasto heater, it at least helped me find the intermittent fan issue and prevent a fire...
 
Last edited:
Check that MHM, will do.

Okay, started on the various diagnosis at least as I can fathom.

The Timer Check. When I press the Instant-On to ON, meter is showing 10.11 Volts when the Manual states 'Approx 7 Volts'. I assume the difference betwen 10.11 and 7 Volts is showing a Fault at this test ?

It does show a drop to Zero voltage when I then switch in the Instant-On to OFF, but of course it may have failed the first test (above) negating this.

2wfq13b.jpg
 
Next, I run the first test of the Troubleshooting Tree

keb0g0.jpg


Result: Meter shows Zero volts at the loom connector to this pin with Timer-Switch Instant-On set to ON (or off).

So, zero volts going to the Webasto unit pin, and a high Volts reading on the Timer.

Wondering on next step...buy and try a new Timer LCD unit, or buy a Diagnostic gadget, both around similar cost.

?
 
eg64nr.jpg


Well, sadly shelling out for a new identical Timer-Clock, I get the same voltage readings.

Eg 9.88V to 10V when the manual suggests I should see 'Approx 7V'.

No life at al from the Heater and no ticking noises from Fuel pumper. A bit stumped.

The manual mentions the 'Reset' procedure removing Fuse-20A in the Webasto loom, but in my TD4's installation Fuse 20A gets referred to being Fuse-7 in the bonnet Fuse-Box - sure enough, it's a yellow 20-Amp, but when I remove this fuse, nothing happens, I still see 12 volts, - should I see 12Volts at the Timer Clock when the 20-Amp fuse is indeed removed?

What next? Should I get a new loom, or a diagnostic gadget?

Any suggestions appreciated. Weather's turning and I could REALLY use my heater ;-)
 
One thing I also want to try - I understand from reading this forum, that if you apply +ve 12v to pin 3 of the 5-pin plug (Thermo Top-C config) the FBH will fire up as this is the feed in from what would have been the timer switch if you had had one fitted.

Q - when doing this test, does the plug next to it, the one with the two thick red and black wires only, need to be plugged in with ignition-on for this test to work?
 
It wont need the ignition on, but I imagine it will need that plug in place.

I am following this thread with interest as mine has packed up and I just need the time to have a look at it.

I dont have the controller on mine, it just runs automatically for a cold start and I fitted a DIY remote control so I could remote-start the unit from the comfort of my kitchen.

However, it just runs the fan and water pump and makes no effort to ignite. The fuel pump doesnt click and after three failed attempts it stops and requires the fuse being pulled to re-set it. The fuel pump is definitely ok as if I tap a 12v feed on its supply wire, it clicks and squirts as it should. The fault seems to be within the webasto itself, which is either not sending the power to the pump or has some other fault preventing it from trying to light.
 
Thanks for the feedback Dave, 'tis been a quiet thread..

I think I definitely need to try force-starting the Heater with the direct 12v 'bypass' before splashing out on a new loom or diagnostic USB gadget.

Plan more work after the weekend as family need her OTR. Will update.
 
Late update, sprained wrist curtailed things.

Did the Pin-2 12v live feed test, making sure 12v was feeding in to the adjacent thicker-wired 2-Pin connector.

No life at all.

Okay, next step:

Front Bumper needs to come off so I can access the Webasto fixing.

Decided I want to get the Webasto unit off and see if I can see what's gone wrong. With the start of the colder weather, TD4's are not pleasant to drive with no Aux heater, so fairly motivated!

Front Bumper removal not easy. Spent ages drilling out the Wheel-Arch Liner screws again, all had fused solid with rust which is a pain in the RS as they can damage the thin flimsy Wheel Arch if brute forced. Truly, what a bugger of a job. Stainless steel replacements will be my friend.

I have all the screws at the top inside the bonnet out, and all the bumper scrivets underneath facing the road (in fact, they were all missing). The 10mm bolts inside the Wheel Arches, well I removed them too. They seem to be fixed to a plastic support frame on the inside of the wheel arch -is that right? seems a flimsy hold for a front bumper. ?

So I think I have all the Front Bumper fixings unscrewed, but, for the life of me, I can't pull the bumper off. I can't see what's holding it. Light stopped play, will look again tomorrow.
 
Hang about... did I say Pin-2 ?

So just to be sure, is it Pin-2 or Pin-3 to do the 12v direct start-up test?
 
I cant remember off-hand, but will have a look later.

Bizarrely, mine burst into life yesterday evening of its own accord when I went out in the car. I guess this is the first time exterior temperature was below the threshold for it to come on automatically.
However trying to force-start it gets me nothing. Must be a wiring fault.


I dont know if its cold enough where you are...perhaps try re-setting it with the fuse, then short out the temp sensor behind the lower grill and start the engine to see if it works?
 
Cheers Dave,

Well I am still figuring how to get the blasted Front Bumper off. Ed China has no competition from me any time soon, sheesh... I have another thread asking for help re the Nudge Bar on that issue.

Once I get the Front Bumper off, I can try your suggestion, I can't get to the sensor right now until the Bumper comes off.

Re. the 3 Fuses - I do seem to have a variation of the Standard Thermo-Top C installation, in that I have 2 of the 3 Fuses easily found side-by-side in the Webasto Loom next to the Webasto Relay, but the 3rd and actual fuse I need for the Reset Procedure is nowhere to be found. From what I can gather, the circuit it has been somehow merged into the under-bonnet Fuse box. When I removed the specified fuse as per the timed Reset Procedure, nothing happens.

Do you know what Webasto wire/contact is meant to be broken when that fuse is removed? So far, nothing seems affected by removal of the fuse and I am not even sure it's the right one.

Man it's cold... we had it easy the past 24 months. Gonna be a cold 'un, NEED that heater! ;-)
 
Okay, finally got to Specsavers and saw I had undone the wrong bolt each side that held the Front Bumper to the rest of the car.

For those as mechanically challenged as me, this shows the mistake I made thanks to very dark, fuzzy images in my Haynes manual...wrong bolt, right bolt..duh..

i73n2c.jpg



The Front Bumper was easy to pull forward AND up slightly to remove it.

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At last, full access to the Webasto unit..

343oqyt.jpg




...more...
 
First check on advice here, was to find the External Temp Sensor for th Webasto, here was where mine was..
2qbhnir.jpg




I then shorted the contact for it with a bit of wire (ground blade-thin at the ends) to fool the Webasto unit into thinking it was cold... sadly, this didn't make it start when I run the engine.
250mudv.jpg



At this point, I was still going to remove the entire unit, but a voice in my head said, try one of yon diagnostic gadgets. So, I have ordered one of those USB Diagnostic gadgets off an auction site for £30. I will report back on how that goes next.

I put her all back together for now, greased bolts, sprayed all contacts with electric cleaner/damp remover until the gadget arrives. With stainless wheel-arch clips, removing the bumper next time should be easy instead of the bloody nightmare it was first time around, what with drilling out all those rusted-solid screws and clips.

Will update as I do it. Hope you like the photo's

Oh, one last thing - anyone know where I can get new Soft Nudge-Bar fixing assemblies? Mine are nearly rotted to useless as you can see.

i1flh0.jpg
 
I have always been told never to pull the two wires of before the 6 pin one as can blow the bord as it pulls voltage down the kbus I've had little dealings of these with the rover 75s I'm going to do the remote relay on my partners and kno the heaters on the 75s was short pin 3 to earth what pin is used to fire these up on the freelander and also do these output to fire the fan up on anouther pin when up to tempreture. Also if your board has failed there is a bloke called French mike that can repair them and he's not expensive
 
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