At a guess, one or both of the big power transistors that are inside the
FSU are failing. If the failure is that the blower motor doesn't run at
all, they are probably failing open. If the failure is either that the
blower motor runs at maximum speed, or a fuse blows, then they are
probably failing shorted. The blower motor probably draws more current
as it ages, and it may eventually be exceeding the power-handling
capability of the transistor(s). When the motor is switched off, it may
also generate a bit of a voltage spike, which may be above the voltage
rating of the transistor(s).
A possible solution is to replace the transistor(s) with ones with a
higher power rating in the same package. Another approach is to improve
the heat-sinking, maybe by adding metal to the existing fins. Or, cut
off the existing fins, bolt it to a huge slab of metal, and relocate the
entire thing away from the blower duct.
As a crutch, you could drop the voltage to the FSU a little bit. This
would slow down the blower, but also might tend to keep the voltages
and currents down to what the transistors can handle. You would need
to know the maximum current you would expect the FSU to draw; this
probably happens when the charging system voltage is at is maximum,
the blower motor is stone cold, and you turn it from "off" to "max".
Then, buy a big rectifier diode with a rating of a few amps more than
that, and splice it in to the power wire to the FSU. This will drop
the voltage by a volt or two all the time. Or, you could put a power
resistor in line instead; this will cause a variable voltage drop
depending on how much power the FSU and blower is drawing at the time.
Keep in mind that in the winter, keeping the windshield clear is a
safety function, so don't drop the blower speed too much.
The tricky part depends on the nature of the control signal to the FSU.
If it's a simple analog voltage, that is easy to generate on the bench
with a potentiometer. If it's some kind of digital bus (CAN?), it is
*possible* to generate that on the bench, but it's probably easier to
get the dashboard heater control out of a junked car and let it generate
To load the FSU, you can either use a power resistor that draws about
the same amount of current as the blower motor on "high" (a headlight
lamp might qualify), or an actual blower motor. The resistor will be
"better behaved" than a real motor.
For a power supply, it depends on how much current the blower motor
needs. You can get relatively inexpensive 13.8-volt power supplies in
ranges up to several amps, designed for running "12 V" equipment on the
bench. Samlex is one manufacturer but there are others. If it needs
more than 10 A or so, it's probably cheaper to just use a real car
battery and charge it when it's not being used.
You should probably arrange it so that there is some air blowing on the
FSU under test. If you are using a real blower motor, you can make a
duct out of cardboard. If not, use something like a 12 V computer case
fan to move a little air across the FSU.
It may also be interesting to have some kind of thermometer on the FSU
case while it is under test.
A good way to figure out what the FSU is actually doing is to probe a
working car with an oscilloscope. This will show you immediately how
the FSU is controlling the blower motor speed, as well as what the
control signal looks like. You can stick a straight pin *through* the
wire insulation as a test point, and then seal up the hole with
electrical tape or silicone sealant.
As has been mentioned, it would be also interesting to cut one of the
blower wires and measure the current drawn by the blower motor. For
extra credit, do this on a new car (or a newly-installed blower motor)
and then compare to a blower motor in a car that has just had its FSU
On one hand, you would like stuff not to break. On the other hand,
spending $100 every two or three years on a car that starts around
$36,000 new is maybe not out of the realm of possibility. (Perspective:
that's one tire or 25 to 30 gallons of gas.)
These cars are apparently sold worldwide. If the FSUs sell for cheaper
in a lower-cost country, enough to offset shipping and taxes, import a
box full of them and make money. :)
On Thu, 21 Mar 2013 21:56:49 +0000, mroberds wrote:
Actually, I was remiss in not stating that the blower motor generally
fails by acting weirdly, often said to "have a mind of its own", and,
most often by a parasitic current draw overnight that kills the battery.
On Thu, 21 Mar 2013 21:56:49 +0000, mroberds wrote:
That seems like an EXCELLENT idea, if we can put some kind
of temperature indicator in the FSU tines, then we can observe
what the temperature is in situ - which might tell us something
about what is overheating these things (assuming heat is the culprit).
I had a dodge caravan that fried its heater AC motor speed control
the connector to the wiring harness detoriates from the high current
and the voltage drop causes the connector to heat up and the entire
Oddly enough I repair roll laminators that apply plastic film to paper
laminators experience similiar failures so I did the following.
Purchased a new resistor block, soldered wires on all the connectors
putting a heavy wire on each one.... Put a pigtail on each one.
Installed resistor block. Its screwerd to the fire wall.
Cut the plug assembly off the harness, stripped all wires, twisted
them together and installed wire nuts on each one.
had the van for years with zero problems for this part:)
I don't have a link, but we had the blower resistor widget
go on an X5 here. And the aux cooling fan motor has gone
twice. There are plenty of threads online about many people having
those problems. Oh, and don't forget the
nice X5 feature where the cable that they use to hold up the
windows snaps, sending the window crashing down inside
the door, breaking it into a million pieces. Had that happen
twice too, once while the car was just sitting in the driveway.
Other time was driving down the highway.
Then there are their defective rubber parts. Like the boot on
the intake manifold that cracks in just a few years. Or the
CV joint boots. I've had lots of cars with CV boots and
only on the X5 do they fail every 20K miles. I've seen Honda CRVs
that went 200K miles with no failure.
On Sat, 23 Mar 2013 07:20:44 -0700, jim beam wrote:
As for me, I fell sway to all the people saying how great the bimmer was.
It was only after I owned it, that I realized that BMW engineers knew
how to design a suspension and a drive train, but they had no idea
how to build a machine.
To their credit, some people say it's not the engineers fault as
they probably know by now that every single Bosch 5.7 ABS control
module fried in every one of the vehicles it was placed in, and that
the final stage unit cooked itself to death in every single BMW it
was ever placed in, and that the 2-bar plastic cooling system
sprang a leak on almost every single BMW ever built, etc.
In fact, there's absolutely NO WAY BMW can't know about these
egregious engineering flaws. So, the common conclusion is that
their customers don't care - so why should they.
To me, it smacks of 3rd-grade engineering from BMW, so, that's why
I, for one, am amazed (being an owner myself), how sophomoric BMW
engineering really is.
Disclaimer: Yet, the drive train is phenomenal!
honda use a "plastic cooling system". it's not infallible, but you can
get 15+ years out of the first one. there's no reason bmw couldn't
achieve the same - if they wanted to.
that is the catch - bmw target a certain type of buyer that typically
won't keep a car more than 3 years. after that, they don't care and bmw
can safely switch to "maximize parts sales/write off the old cars and
sell new ones" mode.
in europe, bmw have been aggressive leaders in "recycling" and spend a
lot of money advertising the fact. in practice however, it means that
they buy used cars back and have them scrapped, thereby keeping used
parts off the market - the mba's have done their math.
it depends on perspective. i agree that some appear to be extremely
rudimentary, but that is contradicted by the fact that they spend a huge
amount of money on r&d, and have boatloads of phd's on staff. they were
also rescued by a bunch of mba's in the 70's and have had a root and
branch focus on design life ever since.
On Fri, 22 Mar 2013 23:42:00 +0000, R. Mark Clayton wrote:
Of course. Nothing I've ever written is not well documented.
I'm not sure "which" common problem you're asking about, so, here is
just a sample of the most-common problems that afflict almost every
BMW E39, E38, and E46 (I'm sure there are others but I'm only familiar
with those models that use the M54 engine).
Behr cooling system leaking
Plastic DISA valve breaking & destroying the engine
Cluster pixel tape lifting
MID pixel tape lifting
Hella PBT headlight adjusters breaking
Power steering cap & hose leaking
Trunk wiring loom fraying
Bosch ABS control module frying
I6 VANOS seals deteriorating
V8 valley pan gaskets leaking
GKR/BMW/Valeo FSU/FSR dying
Thrust arm bushings leaking
Ambient temperature sensor breaking
Window regulators breaking
Vapor barrier adhesive leaking
Jack pads falling off
Windshield cover molding crumbling
Driver's seat control switch breaking
Rear center brakelight socket melting
Seat cables fall out causing seat twist
Windshield washer tanks & pumps leaking
BMW roundel paint chipping
Vent trim corner cracking & wood trim varnish cracking
Rear center brake light socket melting
Note: The reference above has detailed links to EACH of these topics above.
On Mar 25, 2:55 pm, email@example.com (Scott Dorsey) wrote:
Maybe it's time to look at this thing like gas and brakes...
You put gas in, you go so far. You put one of these
blower modules in and you go for a few years again.
It's not like they are a $500 or $1000 puter. Don't they
cost like $50? I mean how much is time worth trying
to reverse engineer it.....
This is how people are. At some point intellectual curiosity takes over.
In this case it might actually be worth it, because of the sheer number of
the things out there that are failing.... one person figuring the failure
mode out might save a lot of people that grief.
But mostly it's just intellectual curiosity.
"C'est un Nagra. C'est suisse, et tres, tres precis."
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)
replace "roosters" with "cox" to reply.
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