Having managed to sort out my aux heater, with a lot of help from this forum and elsewhere, i thought of publishing my knowledge, for the benefit of others.
There's still the last mile to go - in terms of enabling remote start, but that's relatively straightforward once the heater is working properly! so this guide is hopefully of use if your heater is misbehaving.
Background about the Webasto Thermo Top C/Z:
Webasto Thermo Top C is a common heater widely used in marine applications. the C/Z is the automotive version of it. the difference is, the C/Z has a modified PCB, which enables it to talk the car's language. In the case of the BMW E53, it talks K-Bus, which is a part of the E53's communication bus protocol. You will notice that the unit has 2 labels. One is the Webasto original, the other is the BMW label with the BMW part number.
BMW never planned our cars to be sold with a parking heater option. therefore the cars are not plumbed to directly provide hot water into the cabin. the parking heater concept seems like an afterthought, doubling up on the aux heater, which was intended to heat up the engine in a cold morning. therefore it works by heating up the entire coolant network which is not very efficient, but works well enough (there is another models with independent plumbing to make it work as a parking heater, possibly the US version, not sure)
back to our cars..
Because the car manufactures incl BMW have made changes to the PCB for it to talk the car's native language, the Webasto company or its dealers who are readily able to help with general thermo top parts are unable to help diagnose or replace the PCB! Go to BMW - they will not give you a PCB, they will try to replace the whole webasto!!
How does the webasto work: The Webasto C/Z has 2 methods of starting up.
1. Normal Operation - with a k-bus command
few important conditions it checks are:
- water circuit temperature < 60°C
- outside temperature < 5° C
- customer requests more heat from their heater
- I’m not sure if it does the usual voltage checks..
2. Telestart – with +12V to pin 1
This method is necessary for telestart beause the car could be ‘asleep’ when telestart is requested; meaning k-bus is asleep!
few important conditions it checks are:
- Popular theory is that it ignores the temperature checks, but I have found that when the outside temp is like 19c, the system starts up, but goes back to the off state
- Low Voltage 9.8 +/- 0.3v (plus high voltage 15.5 +/- 0.3v)
- Also note the MINIMUM time for the startup/shutdown sequence is around 3 minutes, so it is not recommended to power pin 1 for less than 3min. you can damage the unit or make it go into a lockout state. So make sure you make a solid connection, and latch it for min 3 mins before disconnecting.
A Fuel System Complication i've learnt:
E53 has a 2-part fuel tank, way its designed majority of the fuel in the tank is always transferred to the left
The Webasto fuel supply is on the right hand side fuel pick-up, some way up from the bottom of the tank!
Therefore it is not recommended to run the webasto with the fuel light on. this am told can cause all sorts of 'Flame Formation' faults.
Alternatively if the car is at a steep incline with more than even a quarter of the tank full the webasto could still be starved of fuel!
there's a remedy (extend the fuel pick-up line) in the bmw service manual if one wants to be bothered..
Diagnosing the Webasto Thermotop C/Z:
If your webasto is misbehaving the first thing to check is - connect the Scanner 1.4.0 and check for fault codes. The Scanner 1.4.0 is easily sourced from fleabay.
it must be noted that the bmw ecu records just the basic status for the webasto. you can find out if its good or bad (or disconnected) but not necessarily what's wrong with it. I have forgotten where it logs the error, i think its in the AC/Heater section - this is easy enough to find.
If the scanner reports an error that means the webasto has a problem. diagnosing what is wrong with it is next.
To do this, running webasto test software along with the ability to issue k-bus commands is key.
I took the hard but safe path mainly due to my lack of knowledge at that time, with the benifit of hind sight what id do now is actually service the heater first.
in any case, service later, here's what i did:
I purchased the Reslers (USB version)
, which then works with Webasto Test Software which you can download from here
. The test guide can also be downloaded from this site.
Reslers device connects to pin 2 on the webasto, which is the k-bus on the BMW E53.
the sw is able to test individual components of the Thermo Top, as below:
Again it must be noted that the test document seems to be designed for generic car type webasto thermo top c/z although you do specifically select BMW and so on. so i'm not sure if its accurate to the letter.
Most importantly the test harness allows the webasto error log to be cleared. this is vital to make it function once it gets into one of its moods!! (there must be other ways as well, i just have the kit now so i find this convenient)
Testing individual components with the Reslers pointed out 2 issues to me:
1. Glow Plug test showed the below issue
2. Fuel test should have produced a certain amount of fuel over a measured period of time, it didn’t, it produced much less fuel and then the pump stopped!.
1. The fuel pump was faulty or the fuel lines were blocked; and the glow-plug was faulty
2. PCB was faulty and was reporting these units wrong.
3. well, a 3rd as well, any combination of faults was also possible!
At this point initial logic would have got me replacing the fuel pump and the glow plug for starters. I spent a few days trying to figure out where exactly the fuel pump was located, how to replace, etc. Having read a lot of ppl’s experience I somehow had a hunch about the fault being in the PCB. Eventually i thought I should follow my gut feel and that worked! i suspected that it was none of these but the PCB that was faulty.
the PCB on E53 Webastos is notorious if you read through other posts here. possibly because BMW has mucked around with it (to be fair not just them i think all car manufacturer do this, to make it talk their native language)
I called about 7 Webasto dealers to see if they could supply a PCB. Unfortunately none could - as they could only source the standard PCB, not the BMW specific PCB which would talk k-bus!
Around this time, possibly due to the frustration of not being able to source a PCB, curiosity got the better of me, and I dug in deeper, which resulted in doing a good service job on the webasto.
BMW never intended the webasto thermotop C/Z to be serviced. (well, what do you expect, they think gearbox oil, transfer box oil is for life!).
Having said that, the Webasto is like the boiler in your house.
-Only worse cos it burns diesel oil which produces a residue unlike much cleaner gas which your boiler in the house burns.
-Made much worse by us smart as5es configuring it to run as a parking heater maybe half hr extra every day, whereas BMW only intended these units to run a few minutes when the car started up.
So here’s how to service your webasto, which now I believe is necessary, because I think a blocked burner was the root cause of what caused my failure.
NOTES BEFORE YOU REMOVE:
1. do not remove when coolant is hot!
2. you cannot run the car with teh webasto removed cos it obviously opens up the coolant network.
3. every time the plumbing is removed some coolant is wasted. you can run the car with what gets wasted a couple of times, but you do need to top it up.
4. be careful not to drop anything its annoyingly difficult to recover what falls into the engine bay!!
1. Remove the webasto from the car, as below:
A - remove
B - remove
C - ignore (this is a connector along with labels i've fixed to wires on pins 1 & 2 so that i can easily attach/detach the test eqpt without damaging the wires by repetitive connections)
A - remove
B - remove (one can only be removed after lifting the unit so will have to be done last)
C - remove (make sure you have spare fuel line clips in hand, the original i think is a disposable type)
D - the exhaust - just wiggle the unit off once verything else is discon.
2. Remove the plastic covers
A - remove the 4 screws (some have torx, some have philips) and remove the PCB cover
B - pry out the connector cover with a screw driver,
A - main connector, k-bus and the works
B - main power +/- 12V
C - glow plug
D - Air fan
E - Water pump (all the literature talk about the water pump being a part of the webasto, in the E53 the water pump is somewhere else, so this wire goes out to the car)
F - blank - not sure what this is
G - temperature sensor (torx screw) - remove this to remove the PCB
3. Remove the air fan unit
A - remove the 4 screws
Pull up the air-fan section carefully, the diesel inlet stays put. wiggle it out slowly. lubricate the fuel inlet to help if needed.
4. Remove the burner unit and remove the glow plug
A - remove the 4 screws (torx)
B - pull up the metal clip slowly, that releases the glow-plug
C - pull the burner unit up slightly, then pull the glow plug out. it should come out easily. be careful not to break the glow plug, it felt like it could break.
Inside the heat exchanger once the burner is removed:
The burner unit:
now the part that needs service:
A - this is where the burning happens. Glow plug goes right there as well. it was full of black residue. Clean with a wire-brush sort of thing that can be poked in. be careful not to damage the copper coloured mesh at the back, that's where diesel is dosed (it didn't feel very delicate tbh).. in my case the glow-plug and most of the air inlet holes (all around the unit) were blocked with black residue. they all come off easy with a wire brush (unfortunately i forgot to take a pic before cleaning)
Job done! now put all the pieces back together in reverse order.
What else have i found out by now:
- By testing the glow-plug resistance i also knew the glow plug was short-circuited (it shows 0.7ohms on the meter)
- But the faulty glow-plug couldn't have impacted my fuel test so its still the glow-plug plus either the fuel pump or the PCB or both.
So by this point i was pretty much convinced that the PCB was faulty; possibly caused by a blocked burner, which busted the glow-plug, and the chain-reaction?
I searched around fleabay and elsewhere and found a decent bloke on fleabay, and ordered a webasto. breakers don't sell PCBs so i had to order a full unit. while at it i also ordered one that came with a guarantee (why not for a few more £..).
thereupon came a prob: the unit came with the screws paint-marked cos it was under warranty, damn! now i couldn't replace the PCB and glow plug! so i ended up replaced the whole unit.
Tested in the car. JOB DONE! IT WORKED!!
What does this mean:
- nothing wrong with the fuel pump, i didn't even touch it!; although even webasto sw showed a fuel pump issue and the test doc itself said the next step was to go test the fuel pump, next the fuel lines! bollox! appeared that the PCB was in fact misbehaving!
- glow plug - Still thought its busted but couldn't verify it as i couldn't find the reference point for ohms
So now i have a spare webasto with a busted PCB and possibly a busted glow plug. The car is nicely sorted but i still want to get to the bottom of this. So i have removed the PCB, it comes off like this:
I have sent it to a contact i found in Germany, who has a full BMW webasto test harness and claims to repair these units (can't really remember how i found him..) its not really a risk cos i've got mine working with a spare unit.
lets see how the PCB story unfolds...
glow plug is easy enough to replace from any webasto shop
if all goes well i should end up with a fully working spare webasto.
nothing like trying!
there are a lot of documents i've collected re. how to diagnose etc. a lot of ppl in this forum have helped and some have shared material with me. so pls pm if you need any of those i should be able to email them directly.
beyond that was logical reasoning and a bit of common sense. some of my assumptions could be wrong as well.
hope this helps!
whilst waiting for the PCB story to unfold, now i'm working on hooking up the remote start.
few edits to make the reasoning clearer to understand.