Root cause insight into the common BMW blower motor resistorfailures

[Bimmer Owner]

One key question in all this is if the interface from car to "resistor
block" is some kind of simple digital interface, ie it sends some bits
that get interpreted as "go to speed 3" or does it send a PWM signal.

All I know is that the HVAC controller sends a 2.0 VDC to 7.8 VDC signal
to one of the five pins of the FSU. I presume that directly corresponds
to the desired blower motor speed - but that is conjecture on my part.

How fast are these things failing for those that want to make their own?

The originals fail within about 5 years. I've had my second one fail in
3 years. I think we can safely say about 3 to 5 years is the lifecycle
but nobody really knows for sure (least of all me).

The failure on that X5 resulted in the blower draining the battery
when the car was off. Blower ran fine. Only odd thing in retrospect
was that when the car was off, a couple times I heard a faint noise.

This is one of the classic failure indications! Very very very common!
However, another classic failure indication, other than the dead
battery in the morning, is a blower that has a "mind of its own".

Together, those two sets of symptoms account for 99% of the failures.

Of all the anecdotal evidence presented, I don't think I've ever heard
of a failure being that the system was totally dead.

What that tells us, I don't know.

 

[Bimmer Owner]

one person figuring the failure mode out might save a
lot of people that grief.

But mostly it's just intellectual curiosity.

Exactly!

 

[tm]

All I know of the HVAC input signal is that it's a 2.0 to 7.8 VDC
signal from the HVAC controller, presumably to correspond to the
various levels of the fan blower motor speed.

But is that a clean DC level or a pulse width modulated signal? If it was
measured with a multimeter, you won't know.

Has anyone probed around the module with a scope? Is that possible?

That and the question about the TO-220 devices. I think it would be possible
to make a better replacement if those questions were answered.

tm

 

[Francis C.]

One key question in all this is if the interface from car to "resistor
block" is some kind of simple digital interface, ie it sends some bits
that get interpreted as "go to speed 3"
or does it send a PWM signal.

Your idea about testing it is correct, however a bad one can work fine
until it gets hot enough for the IC chip to fail. Hvac control voltage is
0-8 VDC.

The load resistor should have a metal case mounted on a heatsink to
dissipate the heat if you are going to run the test more than a few
minutes.

My original 13 spike FSU was replaced twice under warranty, so the car
had 3 FSU's. When the 3rd old style failed i replaced it with the new
design FSU. That was 8-9 years ago, it is still working. One thing not
considered in your post is how many did not use OEM units, the $75 eBay
ones are junk. The $175 units at the stealer seem to hold up a little
better.

 

[Francis C.]

Bear in mind that the $75 Sitronic Ebay FSU is known to be even
more faulty than the $175 Valeo FSU from the stealer.

I can think of nice test equipment to buy instead of a $175 FSU every
few years!

 

[tm]

Exactly!

I don't even own a BMW. After this thread, I don't think I ever will.

 

[Bimmer Owner]

All I know of the HVAC input signal is that it's a 2.0 to 7.8 VDC signal
from the HVAC controller, presumably to correspond to the various levels
of the fan blower motor speed.

Here is a picture of the BMW E39 HVAC/IHKA controller and sampling fan.
http://www4.picturepush.com/photo/a/12514687/img/12514687.jpg

I'm googling for specs as we speak.

 

[[email protected]]

But is that a clean DC level or a pulse width modulated signal? If it was
measured with a multimeter, you won't know.

The other possibility is that it's a digital command signal of
some kind. I don't know how they typically do that, but if a
0 is 0 volts and a 1 is 12V, for example, looking at it with a
volt meter, you would see a range like that given.
They do have that 16 pin chip there, doing something.
It might receive the command and then output the appropriate
PWM for rest of the circuit.

 

[tm]

I don't think Fluke makes much in the way of current probes for DC with
appreciable sensitivity. The i1010 is sensitive enough for this sort of
job, but not for a lot of other things you might want. They do make some
fancy intelligent probes but they're all more expensive than just buying
a Fluke clamp meter like the 365.

That said, I have a cheapo Extech 380947 and it's not built like the Fluke
but it's sensitive enough to detect small ground leakage currents.
--scott

I agree that the Extech meters are a good buy for the money. I have the
380947 (400 amp) and the 380942 (30 amp + voltmeter).

They are really handy to have in the toolbag.


tm

 

[Scott Dorsey]

All I know of the HVAC input signal is that it's a 2.0 to 7.8 VDC
signal from the HVAC controller, presumably to correspond to the
various levels of the fan blower motor speed.

Well, that's about what you need to know. Game over.
--scott

 

[Nate Nagel]

What does ROHS mean?

Restriction of Hazardous Substances; that is, no lead (among other things.)

http://en.wikipedia.org/wiki/Restriction_of_Hazardous_Substances_Directive

nate

 

[Bimmer Owner]

That heatsink is small.

Here's what the heatsink looks like when I cut into it today:
http://www4.picturepush.com/photo/a/12515572/img/12515572.jpg

 

[Scott Dorsey]

That's a good theory except why would the resistors not be attached to the
heat sink?

Because they draw no current, they only set the base bias of the power
transistors.

There are still open questions that until answered we are just speculating
with educated guessing.

1) What exactly does the control signal look like on a scope?

It's a variable voltage.

2) The two devices, mosfets or transistors? Any part numbers?

Still unknown.

3) Waveforms on the motor power line for the different speeds.

Reported as DC.
--scott

 

[tm]

I think the IC is a dual, high side motor driver IC and each
transistor has a large emitter resistor with different values. That is
the metal strips on the pins by the sets of three holes. That would
give three speeds & off. Like a three way lamp with 50 + 100 Watt
elements. Turn both on and it draws 150 Watts. This would explain the
failure of the solder joints on the transistors since they are used in
linear mode.

00 would be off
01 would be low speed
10 would be medium speed
11 would be high speed

--

That's a good theory except why would the resistors not be attached to the
heat sink?

There are still open questions that until answered we are just speculating
with educated guessing.

1) What exactly does the control signal look like on a scope?

2) The two devices, mosfets or transistors? Any part numbers?

3) Waveforms on the motor power line for the different speeds.

 

[tm]

Here's what the heatsink looks like when I cut into it today:
http://www4.picturepush.com/photo/a/12515572/img/12515572.jpg

Ha, keep going!

 

[Bimmer Owner]

They do have that 16 pin chip there, doing something.
It might receive the command and then output the appropriate PWM for
rest of the circuit.

Someone had scoped the whole board, and it was DC voltage everywhere
(according to that reference). It's pretty clear there is no PWM.

The 16-pin surface mount chip seems to be a automotive temperature
compensated voltage regulator with a huge voltage range, according
to a lookup of the part number on it.

Here is the Elmos 10901D chip of my FSU as I cut it open today.
http://www4.picturepush.com/photo/a/12515632/img/12515632.jpg

I wish there was a way to get rid of that heavy fibrous plastic goop!
(What is that black fibrous tough stuff anyway?)

 

[Nate Nagel]

I don't even own a BMW. After this thread, I don't think I ever will.

Like I said before, don't drive one then. It's kind of like going on a
date with that unbelievably attractive female type who is also smart,
witty, fun to be around, actually seems to like you, and oh by the way
is completely mentally unhinged.

Suddenly you find yourself putting up with all sorts of stuff that you
wouldn't, otherwise... (now that said, touch wood, current ride has
exhibited none of the known issues... which reminds me, I need to call
and schedule the battery cable recall @ the stealership)

nate

 

[tm]

Because they draw no current, they only set the base bias of the power
transistors.


It's a variable voltage.

Are you sure? It seems it was measured with a DMM, not a scope. A PWM signal
would just look like DC to a DMM.
Since it was reported as "2.0 to 7.8" volts, you would not get those
significent figures with a scope.

Still unknown.


Reported as DC.

Any evidence it was checked with a scope? Again, a PWM signal will just look
like a DC level to a DMM.


Let's see what the autopsy shows next .

 

[tm]

Like I said before, don't drive one then. It's kind of like going on a
date with that unbelievably attractive female type who is also smart,
witty, fun to be around, actually seems to like you, and oh by the way is
completely mentally unhinged.

Suddenly you find yourself putting up with all sorts of stuff that you
wouldn't, otherwise... (now that said, touch wood, current ride has
exhibited none of the known issues... which reminds me, I need to call
and schedule the battery cable recall @ the stealership)

nate

--

LOL. There's more truth to that then you may think.

 

[Bimmer Owner]

I think the IC is a dual, high side motor driver IC

It might be, but this Russian site intimates it's a temperature
compensated voltage controller.
http://tinyurl.com/crg2sms
http://kazus.ru/schematics/electric...%DF%D2%CE%D0%20ELMOS%2010901D&nohistory=1&h=1
http://monitor.espec.ws/section27/topic189041.html
http://item.taobao.com/item.htm?id=13918440884

Translation below:
REGULATOR ELMOS 10901D
Found: 100 Showing: 1 - 10
Car Voltage Regulator
Category: Car
Source: Radioland country Electronics
Temperature controller cabin air KAMAZ
Category: Car
Source: Plans radiokonstruktsy
Simple Temperature compensated voltage regulator. Controller together with thyristor-transistor electronic ignition unit with a long spark, ensuring the rapid start-ups at various operating conditions, allowed to increase battery life of up to nine years.
Category: Car
Source: For the life of a soldering iron ...
Regulator for automotive windshield
Category: Car
Source: MASTER KIT
The controller measures the wiper-this control is designed to use regular mode switch blades and is contactless.
Category: Car
Source: For the life of a soldering iron ...
Temperature compensated voltage regulator device in some ways superior designs. The controller can be used as a universal device is suitable not only for mounting on any car, but everywhere, where the generator rotor speed is variable (eg, wind power). Choose the appropriate control elements, it can be easily adapted to work with any voltage (up to 400V) and excitation current (tens of amperes).
Category: Car
Source: For the life of a soldering iron ...
Voltage regulator 2012.3702, 22.3702, 221.3702
Category: Car
Source: For the life of a soldering iron ...
Voltage regulator 201.3702
Category: Car
Source: For the life of a soldering iron ...
Voltage Regulator 13.3702
Category: Car
Source: For the life of a soldering iron ...
Voltage regulator RR132A, 1112.3702
Category: Car
Source: For the life of a soldering iron ...