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Discussion Starter · #1 ·
I have a 2015 VW T5.1 Transporter BiTDi 32 4motion. After the ignition is turned on or the engine is started the radiator cooling fan comes on .There are no indicator lights on the dash to say there is a fault. The control module for the fan is in the fan itself and i believe is controlled by PWM signals that increase or decrease the speed of the fan. The 12v and earth conditions to the fan are all ok but the PWM wire (White) is a problem. I don't know what the OFF signal condition is and also the ON. All the coolant sensors have been changed. Basically i am trying to prove if the fan is faulty as it costs £800 due to it being a 850 Watt fan. I down loaded a VW workshop manual which gave me the wiring diagram of the fan but the control module is solid state technology.
Anybody any ideas
 

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Discussion Starter · #3 ·
Maybe engine coolant temperature sensor has a fault best to get it scanned and check faults and live data signals
All the coolant and A/C sensors have been checked and are working properly.
The voltage conditions to the fan are all correct except the control wire.
With the ignition ON this wire has 0.5v , this i believe is the off condition for the PWM.
The ECU then controls the fan speed by increasing the voltage of the PWM signal.
However this voltage stays at 0.5v so the fan shouldn't be OFF.
I am trying to test if the fan is faulty due to its cost to replace (£800).
This vehicle has only 48000 miles on the clock and it has had to have a new timing belt, EGR valve and now the possibility of a faulty fan that i have only ever heard once. So much for German engineering
 

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With the ignition ON this wire has 0.5v , this i believe is the off condition for the PWM.
The ECU then controls the fan speed by increasing the voltage of the PWM signal.
As a general observation, that's not how PWM works. PWM works by sending a pulse of varying duration, not of varying voltage. So if a greater fan speed is needed, the duration of the "on" state is increased. The voltage won't change by any significant amount.
 

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Might be useful to have a read of this thread;

 

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Discussion Starter · #6 ·
As a general observation, that's not how PWM works. PWM works by sending a pulse of varying duration, not of varying voltage. So if a greater fan speed is needed, the duration of the "on" state is increased. The voltage won't change by any significant amount.
Thanks for your reply.
All i need now is to know what the voltage is and its duration ON for the fan to remain OFF. Also the duration of the voltage pulse ON for the fan to be activated. I believe the PWM to the fan is ON when the ignition is on.
When i acquire an oscilloscope i should be able to prove if the ECU is sending a PWM signal to turn the fan on. If it isn't then i believe that the micro processor in the fan is faulty which means another expensive job for this vehicle.
Any ideas where i could find this technical data of the PWM
 

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I don't know, but I would guess it will be obvious when you look on a scope. I ~think~ you should also be able to see a significant difference if you look at the signal on a multimeter AC range - as the pulse length increases the AC voltage will appear to rise because of the way a typical multimeter calculates AC voltages - but I'm not completely sure, as I've never tried. I would expect that when the fan is off, the pulses will still be there, but very short duration - just enough for the ECU to detect that there is load on its output.

On my van, the most annoying thing would be getting the engine to a temperature where the fan is commanded by the ECU to be on. In normal driving it almost never happens on my 2013 Kombi (but it's not a BiTDi).
 

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Discussion Starter · #8 ·
I don't know, but I would guess it will be obvious when you look on a scope. I ~think~ you should also be able to see a significant difference if you look at the signal on a multimeter AC range - as the pulse length increases the AC voltage will appear to rise because of the way a typical multimeter calculates AC voltages - but I'm not completely sure, as I've never tried. I would expect that when the fan is off, the pulses will still be there, but very short duration - just enough for the ECU to detect that there is load on its output.

On my van, the most annoying thing would be getting the engine to a temperature where the fan is commanded by the ECU to be on. In normal driving it almost never happens on my 2013 Kombi (but it's not a BiTDi).
I have ordered a pocket oscillator and looking at some you tube videos it appears that the voltage is similar to what a coolant sensor sends (about 0.5 to 1v). This is the DC reading i am getting on the control wire with my multimeter but until i get my scope i don't know what the width is. On another video an Audi A3 had the same fault as me but in its case the control wire was dis to the fan so the fan turned on as a fail safe. This means to me that if the fan cannot detect the PWM condition it will turn on. In my case the dis must be in the fan. To change the fan you have to remove the whole front of the vehicle and remove the radiator.
My scope is due on the 20.04.2021 so i will let you know how i get on.
To simulate the van overheating so that the ECU commands the fan to turn on, use an old sensor. In my case there is a sensor on the output of the radiator at the bottom, unplug the sensor and plug it onto your old sensor then heat the sensor up with a heat shrink gun. This should turn the fan on. This way you don't have to loose any coolant. You Tube has a number of videos on how to test coolant sensors.
To my knowledge my fan has only been on once after pulling my caravan up a steep hill.
When i first had this fault my garage man plugged in the computer and the vehicle hadn't even done a regeneration as there was only 7% soot in the DPF.
Anyway i shall keep you up to speed on my struggles with the VW
 

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When i first had this fault my garage man plugged in the computer and the vehicle hadn't even done a regeneration as there was only 7% soot in the DPF.
If my van is anything to go by, the DPF should regenerate roughly every couple of hundred miles or so, and the amount of soot will simply show approximately where you are in that cycle. If he had looked around a bit more he could have found the place where the ECU records "Distance since last regen". Note however that this is the distance travelled in metres - not kilometers!
 

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have a spare control module if want to try it ..will need the double check the part number first.
 

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Discussion Starter · #11 ·
have a spare control module if want to try it ..will need the double check the part number first.
Thankyou but the control module is in the fan.
At the moment i am just trying to confirm that the fan is faulty or something else is telling the ECU to turn the fan on. It could be a faulty ECU. With a VW what ever it is will be expensive.
 
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