Root cause insight into the common BMW blower motor resistor failures

[Jamie]

A few car manufacturers use resistor wire in the harness leading to the motor connection at the blower box.

This lowers the Q significantly giving you a voltage drop of course, but it also reduces electrical noise and helps suppress the wheeling voltages.

Blower motors in this case are normally designed to operate lets say

8 volts for example, for full RPM.

I learned this years ago when going through the pain of removing the blower in an air box of a Chrysler product, only to find there was nothing wrong with the motor. Symptoms led on to the fact there was since the output of the speed control circuit was alive and happy but no obvious connection to the motor. If I had unplugged it from the air box before pulling that all apart, I would of noticed it.

The problem was the resistor wire in the harness which had open at the crimp point, also in the harness.

Jamie

[clare]

Definitely not, if you already have a multimeter - but it is easier for the guys who can't figure out how to do it without butchering the wiring harness.

[Michael A. Terrell]

That type shouldn't be allowed to own any tools. They generally do more damage than good. If they do get something to work, it rarely lasts because they have no clue what because the problem.

I've seen too many vehicles that some idiot cut and patched back together. One stepvan I bought years ago had a damaged harness and I talked them down almost $1000 on the price. It was coming off lease from a fleet, and they wanted to fix it themselves. i pointed out that if they could repair it properly, it wouldn't be in that condition.

[Michael A. Terrell]

All those photos only show one side. I full reverse engineering should be done to draw a full schematic but I've never had my hands on that module. It would probably take a couple of them, because ot the potting.

Have you looked at the National Semiconductor (Now part of T.I) 'Simple Switcher' series of controllers? Generally only one inductor and a couple small electrolytics. A lot simpler than older designs, and little noise because of the small footprint.

[Bimmer Owner]

The 40 amp fuse is barely accessible (as can be seen from the photos). It's not even easy to pull the fuse & even harder to replace it. So, all I was saying was that it's actually rather difficult to insert test leads into the empty fuse #F76 fuse holder.

I'd wager it 'can' be done - it's just going to take an hour or so to get the leads in place.

[Bimmer Owner]

That's an idea.

[Bimmer Owner]

I doubt anything was removed since all the authors of those pictures are expressly NOT trying to remove anything.

Those round metal "dots" in the pictures are the five pin connectors of the harness connector.

[tm]

So go back to measuring at the battery terminals. Do you have or can you borrow a clamp on DC ammeter? They are great for this sort of problem. You don't even lose any skin that way.

[tm]

Are there any other pictures of the module showing if or where the transistors are attached to the heat sink?

Has anyone ever fully dissected the unit so you can see what is under the PC board? Maybe an X-ray from several angles done at the dentist?

[clare]

Bet I can do it in less than half an hour - without the MaxiTester and in about 5 or 10 minutes with it.

[Bimmer Owner]

These photos show both sides.

Nothing was removed, so I can't figure out WHAT you guys are saying is the transistor removed.

Can you circle one of these pictures to show WHERE you think something was removed?

[Bimmer Owner]

That makes a lot of sense!

Plus, it's easier to hook up leads to the harness connector than it is to get a DMM lead on the impossibly hard-to-get-to 40Amp Fuse F76 for the blower motor.

[Bimmer Owner]

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 CCV clogging Bosch ABS control module frying Cupholders breaking 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.

[Bimmer Owner]

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!

[Bimmer Owner]

I'd be very happy to see pictures of the test leads in situ because I personally tried (and succeeded) in getting the 40 amp blower motor fuse F76 out and back in, but I wouldn't want to do it more than once in my life.

From memory, here's what I did: . I moved the passenger front seat as far back as I could . I lowered the passenger front seat back as far back as it goes . I removed the ignition key and disconnected the battery negative lead . I removed the panel from the bottom of the glovebox . I removed the Phillips screw and panel off to the passenger left kneecap . I lay upside down on the flattened passenger seat, head in the footwell . I located the general module III (GMIII) . With my arms bent wildly arms over my head, I disconnected harness connectors . The first enigmatic connector was the white connector X332 . The next diabolical connector was the small black X253 . And the last puzzling connector was the large black X254 . By now, I could slightly see the yellow 40 & red 50 amp fuses F76 & F77 . With a flathead 1/8" screwdriver, I lifted the yellow fuse F76 up & out . That took about an hour or three. . Putting the fuse back was even harder than removing it

[Bimmer Owner]

All I have are the following: These photos show both sides.

Nothing was removed, so I can't figure out WHAT you guys are saying is the transistor removed.

Can you circle one of these pictures to show WHERE you think something was removed?

[clare]

If the engine desnt burn to the ground due to oil leaks, or overheat or run out of oil, because of all the problems with "ancilliary systems"

[Scott Dorsey]

Okay, notice on the lefthand photo, there are two sets of three solder joints on the lefthand side of the board, which show signs of recent rework. There are TO-220 transistors attached to them, which are behind the board and you cannot see.

On the righthand photo the board is reversed... you can see two sets of three holes on the righthand side of the board which is where those TO-220 transistors were attached. You can see that they overheated the board and lifted pads in the process too.

But you cannot in either of these photos see the transistors or what the part number on the face of them is. Knowing what kind of transistors are used will go far toward explaining some possible failure modes.

--scott

[trader4]

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.....

[tm]

Yes, what Scott said. Where are the two transistors that were soldered in the pair of three holes on the right of the right photo.