Webasto Air Top 5000 installation.

Hello Pablo,

nice to hear that you fixed it. My Webasto has a faulty control unit, too. Did you fix it by a new mosfet? Which one was it?

George13

 

Using Webasto Thermo Test, fault code is 2002, value is: "no start".
Heater is a Thermo Top Z/C (water), it has the same BTS 141 in the control unit, which controls the glow plug .
Thermo Top Z//C has no separate flame sensor, but uses glow plug as a flame sensor, as soon as glow plug is switched off (by measuring resistance, wich differs when unit is burning fuel). You might know this all, of course.
Heater starts normally, glow plug is on (burner insert/glow plug is new). Burner starts, fuel pump working, water gets warm (water pump is ok). After 90 seconds glow plug is switched off, FD "lamp" on Thermo Test is red, but "flame detector measuring" is cancelled after a few second and fuel pump gets switched off. Consequently flame exstinguishes.
Same cycle repeated, again fuel pump gets switched off after af few seconds. Unit turns off normally.
As I said, fuel is burning and water gets warm during these two cycles.
I ordered the BTS 141 already, will arrive tomorrow. The mosfet controls the glow plug, so it must be responsible for ohm measuring, too? Resistance is no problem, I think, I exchanged the burner insert with glow plug for a new one already

 

You were right, it was not the BTS 141. The fault was the large 1R0 SMD resistor above it, which obviously controls the glow plug when it acts as flame control. The glow plug is new, so I supposed it was ok.
The resistor's actual value was somewhat higher than 1 Ohm. I exchanged it with an ordinary metal film resistor 1 Ohm, 1% (not SMD), and now the heater works perfectly!
The hint came from a specialist in France. But thanks for your help, too.

 

How many watts should this shunt/resistor tolerate?

 

I´m having more or less the same troubles, but the test software indicates glow plug/flame guard short circuit - measuring 0.005 Ohms.

The mentioned 1R0 resistor measures in at 0.985 Ohms. Could this still be the sinner, or should I look further up-stream.
Appreciate any tips on which component to check

Edit: The 1R0 resistor measures 0.985 _M_Ohm! I missed the Mega, since the value seemed close enough to 1. Guess it's the one after all!
Will replace it and report back

/eLC

 

Hello, do you have a Thermo top C/Z? Does it start up at all?
In model C/Z the glow plug works as flame guard, as soon as glowing is turned off. You might have to exchange the glow plug.

Have a look at the english remarks in the middle of this norwegian page:
http://www.lrforum.com/forum/index.php?showtopic=49869&st=20
It is cited from the UK Landrover forums:
http://forum.landrovernet.com/forum.php
There the corresponding thread is only accessable after registerering.

I exchanged the 1R0 resistor, because my glow plug was new and obviously not the sinner. The resistor's value was a good bit above 1 Ohm. But I only have a cheap Ohmmeter, which is certainly not accurate at such low values.
The new resistor has 0,25 watts, which might be a bit low, but works well until now.

If your Webasto does have a separate flame guard (as Thermo Top T or S), check or exchange that one. It should have brown cables, the glow plug has yellow ones.

 

Sorry for being inaccurate.
I have a Thermo Top C, and the glow plug and burner is brand new.
The Thermo Top reports "Glow plug/flame guard short circuit" and indicates 0.005 Ohms in the Webasto diagnostic software.

I measured the 1R0 in place, and focused on the "near 1 value" (0.985), but obviously missed the Mega on my meter
So, what I´m measuring is the resistance in the rest of the circuit.
Given the common way of measuring low Ohm loads (voltage divider), the 1R0 is needed as a known resistor to measure the voltage drop over the glow plug and calculating the unknown resistance.

I was unable to find a smd resistor with the same form factor, so I ordered an ordinary axial resistor of 1W - hope that will do it
Will report back when replaced.