kbus short on fbh

[psmith]

I think ive got the fault on my fuel burning heater where the fan starts up when i unlock the doors on my tourer. Has anyone fixed this problem and if so was it water ingress on the pcb or did you simply disconnect the kbus wire. If i need a new one can i get a recon unit from somewhere or is it a new one

[Unclefista]

I'm pretty sure the kbus wire is only used if you have the webasto remote/timer.
I'd just snip it

[HarryM1BYT]

Originally Posted by psmith

I think ive got the fault on my fuel burning heater where the fan starts up when i unlock the doors on my tourer. Has anyone fixed this problem and if so was it water ingress on the pcb or did you simply disconnect the kbus wire. If i need a new one can i get a recon unit from somewhere or is it a new one

Just snip the wire at the FBH, but make sure it can be easily reconnected. Its the white/red with almost invisible yellow.

You didn't say - is the FBH working other than this issue? If not working, just unplug entire FBH instead of snipping.

The issue is not water ingress, it is due to a well known and regularly occuring component failures within the PCB. FrenchMike can probably repair your PCB.

[psmith]

Originally Posted by HarryM1BYT

Just snip the wire at the FBH, but make sure it can be easily reconnected. Its the white/red with almost invisible yellow.

You didn't say - is the FBH working other than this issue? If not working, just unplug entire FBH instead of snipping.

The issue is not water ingress, it is due to a well known and regularly occuring component failures within the PCB. FrenchMike can probably repair your PCB.

Thanks for the advice, the fbh does something below 5 deg as i can hear it running. ill snip the wire for now and contact FrenchMike about repairing the pcb.
Just looked at your how to post on fbh's - very good

[HarryM1BYT]

Originally Posted by psmith

Thanks for the advice, the fbh does something below 5 deg as i can hear it running. ill snip the wire for now and contact FrenchMike about repairing the pcb.
Just looked at your how to post on fbh's - very good

Making a bit of noise may not confirm it is working, it could just be the water pump and fan running triggered by the +5C stat. The only proof that it is working, is to listen for the clicking of the pump near the O/S rear wheel or feel the FBH exhaust getting hot.

[psmith]

Originally Posted by HarryM1BYT

Making a bit of noise may not confirm it is working, it could just be the water pump and fan running triggered by the +5C stat. The only proof that it is working, is to listen for the clicking of the pump near the O/S rear wheel or feel the FBH exhaust getting hot.

Ive peeled back the black insulation tape to reveal more of the cable, cut it and fitted bullet connectors to it. Ive then left them disconnected and re insulation taped it back up, so if i need to re-connect it later I can. I'll check the fbh now to see if it actually works using your check method.

Cheers

[psmith]

Originally Posted by HarryM1BYT

Making a bit of noise may not confirm it is working, it could just be the water pump and fan running triggered by the +5C stat. The only proof that it is working, is to listen for the clicking of the pump near the O/S rear wheel or feel the FBH exhaust getting hot.

Tried to test it this morning but not sure if its working or not. I have the 98570B FBH (JEC 104390). Is the open end rubber pipe with an plastic insert in the end an air intake. I ask this as when I started it up this morning it was sucking air in through this pipe. After about 1 minute I could feel the webasto casing was warm and also the pipe with the bleed screw attached to it. After about 2 mins it stopped sucking. I tried to find where the pump was at the back of the car but probably need to get underneath properly and have a good look. Also is the exhaust a stainless steel pipe with 2 90 deg bends in it. The pipe exits to the underside of the car through a cutout in what looks like the engine undertray. I couldn't feel anything coming from it and the pipe felt cold.
Snipping the kbus wire has stopped the fan running when I unlock the doors, incidentaly I seem to remember that air was exiting from the open ended rubber pipe when the fan was running due to this fault - i could be wrong though.

I let the car run for about 10 minutes where the casing/pipe stayed warm but didn't get any hotter. I didn't carry on any more as the engine itself started to get warm and I thought that it would mask what I was trying to do.

Any Ideas?


Just tried again and noticed that the fan does not seem to make the same noise as when the kbus wire was connected. I'm thinking that the PCB needs repairing.

[psmith]

Originally Posted by psmith

Tried to test it this morning but not sure if its working or not. I have the 98570B FBH (JEC 104390). Is the open end rubber pipe with an plastic insert in the end an air intake. I ask this as when I started it up this morning it was sucking air in through this pipe. After about 1 minute I could feel the webasto casing was warm and also the pipe with the bleed screw attached to it. After about 2 mins it stopped sucking. I tried to find where the pump was at the back of the car but probably need to get underneath properly and have a good look. Also is the exhaust a stainless steel pipe with 2 90 deg bends in it. The pipe exits to the underside of the car through a cutout in what looks like the engine undertray. I couldn't feel anything coming from it and the pipe felt cold.
Snipping the kbus wire has stopped the fan running when I unlock the doors, incidentaly I seem to remember that air was exiting from the open ended rubber pipe when the fan was running due to this fault - i could be wrong though.

I let the car run for about 10 minutes where the casing/pipe stayed warm but didn't get any hotter. I didn't carry on any more as the engine itself started to get warm and I thought that it would mask what I was trying to do.

Any Ideas?


Just tried again and noticed that the fan does not seem to make the same noise as when the kbus wire was connected. I'm thinking that the PCB needs repairing.

Ive taken the PCB out as per HarryM1BYT "How To" and removed the 2 silicon blobs from the PCB and measured the three resistors on the image of the PCB. R2 measured 49.6K Ohm so seems ok and R3 Reads 4.7K Ohm so this is also ok. But R1 is open circuit so I have removed the varnish from the surface mount resistors joints annd re-soldered them. R1 now measures 4.7K Ohm. The silicon must have attacked the joint somehow. I'm going to fit it back in and see if it works.

[HarryM1BYT]

QUOTE=psmithTried to test it this morning but not sure if its working or not. I have the 98570B FBH (JEC 104390). Is the open end rubber pipe with an plastic insert in the end an air intake. I ask this as when I started it up this morning it was sucking air in through this pipe.

The large rubber pipe on top is a filter/ air intake.

After about 1 minute I could feel the webasto casing was warm and also the pipe with the bleed screw attached to it. After about 2 mins it stopped sucking.

Casing can get warm from the heat of the glow pin, the only certain way is to feel the exhaust or hear the pump running. Even better - do the LED 2 mod, that makes it obvious what the FBH is upto

You could even fit an LED (as per LED 2) on the PCB as a tell tale

I tried to find where the pump was at the back of the car but probably need to get underneath properly and have a good look.

You can feel the pump, by just reaching your arm under the sill.

Also is the exhaust a stainless steel pipe with 2 90 deg bends in it. The pipe exits to the underside of the car through a cutout in what looks like the engine undertray.

That is the exhaust. When the combustion air fan is running, it will be blowing air out of the exhaust.

I couldn't feel anything coming from it and the pipe felt cold.
Snipping the kbus wire has stopped the fan running when I unlock the doors, incidentaly I seem to remember that air was exiting from the open ended rubber pipe when the fan was running due to this fault - i could be wrong though.

I think you were wrong. So far as I know, it can only suck air in, though if it misfires you can sometime get smoke coming out that way.

I let the car run for about 10 minutes where the casing/pipe stayed warm but didn't get any hotter. I didn't carry on any more as the engine itself started to get warm and I thought that it would mask what I was trying to do.

Any Ideas?

Your resistor tests/ replacements might fix it.




Just tried again and noticed that the fan does not seem to make the same noise as when the kbus wire was connected. I'm thinking that the PCB needs repairing.

I think you are correct!

[HarryM1BYT]

Originally Posted by Unclefista

I'm pretty sure the kbus wire is only used if you have the webasto remote/timer.
I'd just snip it

So far as I have been able to work out, on the Rover the K- bus is only used for some rather iffy diagnostics. On the BMW the hi-line can 'talk to' the FBH to actually control it. The Rover remote seems to just work directly with the FBH to turn it on and off. If anyone knows better, please feel free to correct me.