M52TU MDK. Yikes, P1542. Anyone have notes on connector pin resistance values?

[pleiades]

Has anyone perchance measured the resistance across certain connector pins on the BMW M52TU throttle body (MDK)?


My MDK this past week slapped me with two engine failsafe prog episodes, both on cold mornings around the freezing mark. The second time, I pulled the code P1542, which as many know, seems to be the death knell for these things. First “big” failure for my car since purchase in 2010, and happened in busy rush hour traffic…. Great fun.


I’ve extracted my MDK from the car for eventual replacement. While I ponder what to do about it, I’ve measured the resistance across certain pins on the MDK connector (assuming that might reflect pot condition to some extent). Probably futile, but with the negative probe of a multimeter resting on Pin 5 (they’re actually numbered inside the connector), I get the following ranges as I open the flap from closed to WOT:


Positive probe on Pin 2: 1.8 Kilo-Ohm (flap closed) to 1.1 Kilo-Ohm at WOT
Positive probe on Pin 3: 2.1 to 2.6 Kilo-Ohm at midpoint, then from there back to 2.1 at WOT
Positive probe on Pin 4: 1.1 to 1.8 Kilo-Ohm


I haven’t tried every combination but the above pins seem to be the only ones giving a reading other than 0.


Anyone care to compare notes? I’m especially interested in the readings for a new MDK, in case you happen to have one sitting on a shelf (lol).

[JimLev]

Compared to my 540 TB those values seem VERY low.
Sure those reading weren't K ohms?

[pleiades]

Compared to my 540 TB those values seem VERY low.
Sure those reading weren't K ohms?

These old eyes .... I'll edit those values now, thanks!

[geargrinder]

Yeah. Its what would have been called "TPS" tracks inside the DBW throttle body. Oddly the I6's don't seem to have the "DK" throttle body hassles as often as the V8's. For the M62TU it's definitely 'a thing'. I'm not sure simple measuring things gets you very much honestly. Here's whats happening...

There are dual tracks in the TB's (as well as in the accelerator pedals) for failsafe error detection (so an ant getting into the pedal housing for instance doesn't make the ECU go full-WOT suddenly...) The error code comes from logic in the ECU that compares the values on the 2 tracks and if they get even the slightest bit out of sync, it throws the FAILSAFE and codes. On full DBW it is same for the DBW pedal as well as for TB. Now its my theory that the V8 DME parameters for throwing that error are much tighter and fussy and that's why we see so many 'bad' TB's and failsafes in comparison to the I6 cars, but thats not really here nor there for your situation so...

What could be helpful...

When you do get stranded, there's a couple tricks... For the later full DBW throttle body cars the DME does 'throttle body adaptation' when ignition is turned on, I believe similar for both I6/V8 although I think the actual procedure varies between them. When the DME detects a mild error between the 2 pot signals at startup, at least for ME7, it will first try to lightly scrub the plate itself and see if the error resolves. That's why the motor will go "waah waah waaah" for a few seconds before the ENGINE FAILSAFE code is thrown, the DME is trying to confirm "OK do I really have a problem here". Therefore a first tip is, don't fire up the car TOO QUICKLY on startup, turn the key on and wait a few seconds, that might be just enough. If not, with ME7, you leave the key on for a while (Jim will tell us the number of seconds) without starting and then it goes into adaptation mode, which also scrubs the plate back and forth several times (and further to full travel since the DME doesn't want to go full-open on a no-load motor...). That cycling can be enough to clear the error and get unstuck. On the 'full DBW' I6 its similar although details may vary - my friend w a M54B25 and TB issues used to cycle the ignition 4-5 times, and that would almost always get him going again.

If that doesn't work, with the M62TU at least, usually you can pop the hood, pull the intake pipe, and work the plate by hand back and forth full travel and 'scrub' the potentiometer tracks that way and get it working again. For V8's in my sadly considerable experience, this virtually always works to get rolling again for a while. I6 its harder to get access to the plate, so for M54 boys thats a bit more hassle.

Now I know you have the 'semi-DBW' cable+servo weirdo MDK TB... but those TPS tracks inside it work exactly the same way... with luck, maybe just pumping your cable throttle full to floor and back and bunch of times might scrub that puppy up when you're stuck. I suspect that maybe the M52TU might do a similar adaptation thing with its servo motor on ignition-on, but since you actually have a cable, you don't have to even think about that... next time you're stuck try pumping the heck out of it to WOT w/ engine off and see if it fixes things.

OK.. then beyond that, a number of us have opened up our 'non-serviceable' V8 TB's and cleaned them out with contact cleaner and potentiometer lube with good success. I have an old high miles TB that I rehabbed that way and it works like a champ for a spare. Perhaps you can do same thing with the kooky "MDK" rube goldberg apparatus for a longer term fix?

[geargrinder]

Note from this (if image doesn't show up for you let me know and I'll download and re-host/fix it) the MDK has 4 pots... 1 for the pedal-request side, and one for the actual-plate side. Basically just like the full DBW cars but all glommed into one whacko contraption. Could have been either set of pots that threw the error but if you had BMW proper codes it would probably indicate that more directly unless you found a source for what exactly P1542 refers to on MS42?

[pleiades]

GG man, many thanks for all those details. Yeah I sort of figured measuring just the resistance at the connector pins probably won't be indicative of much, but was hoping someone else has done that and might confirm. My source for the P1542 code is a Scangauge III scanner, not what I usually rely on ... my laptop had bmw scanner 1.4 and BMW tools like INPA on it, all working until I made the mistake of upgrading to Win 10, which literally trashed much of my setup. I have re-installed these utilities and their drivers (wish I could find Ubuntu-ready versions), and assume they will function again, but at the moment, the TB is out of the car along with assorted peripheral stuff.

I am inclined to try and take things apart because usually I can actually make them work again, or at least better. In this case, I think I'm looking at an expensive doorstop and have another (used) on the way. If I can figure out how to non-destructively remove the security nuts on both ends of the MDK shaft, I think I will be able to look at the pots closely and clean them if their surfaces aren't outright scorched or otherwise defective.

The two philips screws holding the plate to the shaft have been staked on their tips. I can see I'll need to be really careful about not distorting that shaft when I try to unstake and remove those. Those security nuts, though.... almost look like turbine blades, lol.

I see that some who've done this recommend deoxit contact cleaner, as it contains a lube component. Can't find that locally yet. Did you actually use this, or have a separate potentiometer lube product at hand?

Note from this (if image doesn't show up for you let me know and I'll download and re-host/fix it) the MDK has 4 pots... 1 for the pedal-request side, and one for the actual-plate side. Basically just like the full DBW cars but all glommed into one whacko contraption. Could have been either set of pots that threw the error but if you had BMW proper codes it would probably indicate that more directly unless you found a source for what exactly P1542 refers to on MS42?

[geargrinder]

I love Deoxit, always have it around. There's multiple flavors for various applications, the Silver/Gold 5/6 versions are what I have and use both for general pot/contact cleaning, both have lubricants in them I think? Some say oleic acid is the magic fairy dust in them but who knows. Anyway RadioShack used to carry this retail but now most all of those stores are belly up. You can get it at other electronic stores if you can find one, but in general electronics supply shops are getting harder and harder to find. Maybe if you have one of those computer shops (Microcenter around here) that has a business for build-your-own gamer type computers and computer repair, they might have it too... Obv can find it online as well... I also keep more generic dry contact cleaner around - that's easy to find under CRC brands and others at normal hardware stores - but you have to notice whether your buying the stuff with a lubricant or not... (I have CRC products of both types in the garage at this moment I think...)

[pleiades]

Ah, I have the CRC contact cleaner in the small red spray can, but I don't know if it has a lube mixed in. I'll research and shop around. Yeah RS has probably closed all its stores around here, but we do have a few consumer electronics shops around. BestBuy maybe .... Mucho appreciate all your help. I've seen pics of scorched pots and the parts themselves look fairly easy to replace if only the Italian manufacturer sold them separately on the market ... These particular TBs probably last rolled off the assembly line in 2000. I think even the replacements from BMW would be from that old stock now.... Pricing has tripled from a few years ago, tho'.


Hmm, found this at a local Guitar Center....

http://www.guitarcenter.com/CAIG/Deo...74115056546.gc

[effduration]

I hope I can contribute to this thread. A failed TB is major stranding item on these cars

Can I suggest you edit the title and add "Throttle body" and/or MDK to the title to help in future searching?

How many miles on your car?

I have changed the Throttle body on my '99 528i (132k) 4 times (four) over the last 18 months. I replace them each time with a used unit that I have bought on Ebay or (preferably) pulled from a parts car that recently ran. Here is how I felt at the 1st, 2nd, 3rd, 4th replacement

1st (120k): Well, I got 120k out of the original, I guess it just went bad
2nd (122k): Gee that didn't last very long. Maybe I got a bad used unit on Ebay
3Rd128k) Why am I replacing this again? - Hey my throttle cable is worn and notchy let me replace that
4th: (130k) What? again? I must have another problem. I'll replace the harness next time,

So, the last one I replaced last August. I have put about 2k miles on car since then.When it fails (not if) I will take intake off and replace engine harness and heater pipes which are overdue. I hope that solves my problem

These units are date stamped. Hold them sideways and look near the black cover up from the bottom. I have seen used OEM units date stamped as recently as 2002.

I have never seen much difference between yellow label and blue label ..I have tried both in used form, with equally poor results.

In my research these units fail: A. When they are disurbed (removed for CCV or cleaning) or B. without warning or as in your case.
in the former case I suspect the round connector is weakened and creates a bad connection - which is what I think I have.
In the latter case (your case) I think the Pots get dirty and/or damaged.


Attachment 619546Attachment 619547

I have several used units lying around as spares. I am a little weak with a multi-meter, but I have one and will give it a try. Where do I see the pin numbers in the connector? I couldn't see any numbers?

Also, In addition to the Hella OEM units, you can actually buy an OEM (appearing) throttle body from Autozone under the TechSmart brand (Part #S20103)..still very expensive..maybe more than the dealer.

https://www.autozone.com/fuel-delive...nit/747326_0_0

I have seen folks on other forums test the M52TU connector in the harness, in response to these pblms and find a break in the elec connection.
As GearGrinder mentioned, I have also seen a post or two where somebody took it apart, cleaned pots and put it back into good service.

[pleiades]

effduration, thanks for your input, obviously you've gone through this multiple times with no lasting "relief."

Yes, title is bad but I'm not sure how to edit after the thread receives replies. Can I do that?

I'm aware of the date stamp and location, and have looked as best I can for the newest used one I could find. I just purchased one that's marked 02 for a 2002 vintage! Somewhere I read that the blue-label versions are newer, and I'm not sure how or why, but they do end with the 414 part number instead of the 383 on the yellow versions.

The pin numbering is inside the recessed perimeter of the TB connector socket itself. Very hard to see unless under decent lighting.

Regarding the connector on the harness. The TIS documents how to reset it so that the little red dot shows up before you try to reconnect it to the TB. Some years ago I replaced all the wear items hidden underneath the intake manifold (CCV, knock sensors, dual temp sensor, fiberglass heater pipes, manifold gaskets, injector and distribution piece O-rings, and some other bits). At that time, I did remove the throttle body but also followed the TIS procedure, so I'm thinking my TB has bad pots rather than a bad connector. If I can manage to remove the security nut on the motor side of the TB shaft, I will find out, but these things are arguably built to never ever be opened up again.

I think I will end up testing the harness to the DME before plugging the TB back in. In the meantime, I will have to put aside some $$ for a new TB unit. Cheapest I've seen is around $685 on the usual e39-friendly sites.

[pleiades]

....
I have seen folks on other forums test the M52TU connector in the harness, in response to these pblms and find a break in the elec connection.
As GearGrinder mentioned, I have also seen a post or two where somebody took it apart, cleaned pots and put it back into good service.

effduration, do you by any chance have a link to those M52TU TB threads? Also, to clarify, I have come across a couple of threads about opening up and repairing the TBs on other e39 engines (M54 and M62) but none about the TB on the M52TU. If you have any links to those, I would appreciate if you can share.

I managed to remove the security nut on the servo motor side by destaking it and pressing a 13mm 12-point socket down on top before turning CCW. It wasn't very tight. However, after removing that and the large cylindrical magnet underneath, I find that the exposed plastic pot casing has a brass center sleeve that seems to be press fit onto the shaft. I currently see no way to go forward beyond forcefully pressing or tapping the shaft out, toward the cable spring end. I had no trouble removing the throttle plate from the shaft and also removed the six small torx screws from the black ABS cover on the sprung cable-guide side. However, something is still holding everything together. I'm guessing the shaft goes through a couple of bearings in addition to the brass pot sleeve.

Anyone?

[effduration]

Here are several relevant links and threads:

http://askatech.com/AskATechLive/for...er.ashx?a=4867

http://www.bimmerfest.com/forums/showthread.php?t=600546
(see post #12)

https://www.bimmerforums.com/forum/s...-Throttle-Body

https://www.bimmerforums.com/forum/s...)-plausibility

https://www.bimmerforums.com/forum/s...tle-body-(MDK)

(Different but similar)
http://www.e38.org/e32/e32_throttle_body_cleaning.pdf

http://twrite.org/shogunnew/files/fo..._Refurbish.pdf

[JimLev]

For years I'd get Failsafe Engine Program. The codes were pointing to the TB and the pedal pot. For 5 years it would only happen maybe every 6 months, shut the engine off then restart it and all was good for a long time.
Replacing the TB and pedal pot didn't help. Then last year I started getting Failsafe every 2 weeks to 2 days. I replaced the connector, pins, and wiring to the TB and MAF. Only did the MAF wiring as the insulation was dried out and cracked.
Knock on wood, everything has been fine, no codes.

[Aussie528iT]

I hope I can add a bit more info to this thread.
A couple of times over 150K kms of ownership I have had throttle potentiometer plausibility errors.
INPA came up with these 2 errors:
169 MDK output stage control after diagnostic failure
118 Plausibility signal motor throttle valve - sensor potentiometer 1 and 2

Each time I took off the throttle body and operated it multiple times from closed to fully open and that seemed to clear the problem. So I concluded that the problem was contaminated pots and the full cycle of operation cleaned the gunk off.

I carried out some measurements on the 4 pots with the throttle fully closed and fully open

Results are as follows.
Between terminals:
2 - 3 1740/970 ohms
2 - 5 1920/1259 ohms
1 - 6 1706/967 ohms
1 - 8 1897/1252 ohms

I didn't measure between terminals 2 - 4 or 1 - 7

The 2 links below are for the M52TU throttle body and give info about how it works and the wiring diagram between the throttle body and the DME.

https://www.newtis.info/tisv2/a/en/e...-valve/uhczEhL
https://www.newtis.info/tisv2/a/en/e...tuator/X3yjrjG

I hope this helps.

[effduration]

Pleiades - As post author, I believe if you select "edit" on your original post and then select "Go Advanced" from the edit screen, you will be able to modify the title.

[geargrinder]

Some good stuff goin' on here... Mostly I can't comment on specific M52TU stuff obviously and its great that somebody with more experience on those is ringin' in but maybe few more things to add...

Hmm, found this at a local Guitar Center....

http://www.guitarcenter.com/CAIG/Deo...74115056546.gc

Exactly. That's the stuff. Duh I should have thought about GC - at least they aren't out of business... yet... (that's a whole fascinating story actuallyl...) Read the comments there and you'll see how evangelistic people get about that stuff!

Then this type of 'dry' cleaner for big washdowns. Typically w/ something like this I'd hose the whole inside w/ the cheap dry stuff first, but don't move the pots until I then spray the De-oxit on the tracks to clean them up. That keeps you

https://www.homedepot.com/p/CRC-QD-1...30-6/202262505

Yes, title is bad but I'm not sure how to edit after the thread receives replies. Can I do that?

Nope you cannot, but you can axe Jim to use his godlike powers to do it for you.

I have several used units lying around as spares. I am a little weak with a multi-meter, but I have one and will give it a try.

Yeah - that's OK to do and Aussie's info gives a good 'blueprint' its always fine to check that, but here's why it isn't really a reliable test. The ECU's diagnostic routines might see two types of problems that could measure perfectly fine on a static pin-to-pin measurement:

1. Spot contamination on the tracks, so as the pot sweeps it 'hiccups' for a second.

2. General parallel tracking with the pot pairs, so that they are not quite perfectly in sync, maybe because of wiper contamination, maybe because of connector, etc.

In the case of 1, the contamination might come and go and so even if you watch a multi-meter and sweep it, you might miss the blips as you've disturbed the crap temporarily (like the way scrubbing the throttle plate works...) but it will come back.

So what to do... In the case of 2, kinda hard to check.. with a generic electronic dual pot like below, there's a nifty little pros wiring trick you can do with a multi-meter set to ohms and check if the 2 sides are tracking in parallel, but with a special custom device like these not sure if its possible, would have to know the schematic pinouts better for the pot pairs. Better would be to almost setup a bench simulation of working conditions, feed the TB 5V from a power supply, then track the parallel outputs, and then on a dual trace scope set to a high resolution that'd be pretty easy to line up and see tracking errors pretty quickly. For somebody w/ an electronics workshop like me or Jim that'd be fairly easy but for most home garage guys that's outa the question.

I'm guessing the shaft goes through a couple of bearings in addition to the brass pot sleeve.

Not sure if this is similar, but on the M62TU & M54 type later era of TB's there's a blind pin driven into the housing to stake the shaft in place. Without a machine shop its nearly impossible to remove. AFAIK Dinan does the overbored TB's they drill that out on some kind of precision jig, but in a home-shop setting it's nearly impossible, ie. drilling out a hardened pin out of a soft aluminum housing. I looked into that for a long time. I'm sure pro machinists can do it but it sure looks hazardous to attempt even w/ 2 drill presses in the house.

When it fails (not if) I will take intake off and replace engine harness

Then last year I started getting Failsafe every 2 weeks to 2 days. I replaced the connector, pins, and wiring to the TB and MAF. Only did the MAF wiring as the insulation was dried out and cracked.
Knock on wood, everything has been fine, no codes.

Yep. In case '2' above, some of the tracking error that would cause an ECU to get freaked out can be down to external resistance added in a harness or connectors clearly. And you can easily see how something like that could be intermittent and affected by temperatures and/or humidity etc.

M54B25 friend had exact same resolution with a car that was a 'nightmare' car, went through handful of TB's, a crap shop replaced tons of other stuff like the DME (you know how I feel about "REPLACE THE DME!" diagnoses!!) and while it would work for a while, nothing worked permanently, never knew when he'd get stuck w/ a FAILSAFE.

Finally tossed a new engine harness in, and... voila. Car's run perfect ever since. Well was until he thrashed the crap out of it and burnt a valve, then we swapped an M52TUB28 block in under the M54B25 parts, but that's a whole different story.

Each time I took off the throttle body and operated it multiple times from closed to fully open and that seemed to clear the problem. So I concluded that the problem was contaminated pots and the full cycle of operation cleaned the gunk off.

Yep - short of harness problems (which effdur may in fact have) that's just like what we see w/ the later cars.

Last suggestion - I didn't chase all those thread links, so not sure how people are rehabbing these, but for the M62TU TB some guys 'hacked' the cleaning operation by just drilling a hole in the plastic case to stick a spray-straw in and blast cleaner through, then taping it up afterwards, vs cutting the whole cover open like I did. Wonder if same might work here. You want to be super careful on drilling and try to not not let the drill shards fall inside. IIRC somebody used a soldering iron to bore a hole instead for that reason, although I think you could get away with drilling as long as you're careful and use tricks like coating the drillbit with something sticky to grab all the bits. And anyway, an actual shaving of plastic should be heavy enough to fall to the bottom of the case and stay there... I think its more like dust and film that we are trying to clean off than a big plastic particle.

[geargrinder]

The 2 links below are for the M52TU throttle body and give info about how it works and the wiring diagram between the throttle body and the DME.

https://www.newtis.info/tisv2/a/en/e...-valve/uhczEhL
https://www.newtis.info/tisv2/a/en/e...tuator/X3yjrjG

I hope this helps.

Good stuff there. To quote a little bit...

Emergency operation function

If a fault occurs during operation a corresponding fault code will be stored in the fault code memory of the DME control unit. Emergency operation is assumed depending on the severity of the fault:
- Indicated permanently in the check control
- Changeover to potentiometer 2 in the event of a fault in potentiometer 1
- Selection of the correct potentiometer in the case of plausibility errors by means of a model based on the measured mass air flow.
- Cut-out of an output stage of throttle valve and safety fuel cut-out in the event of the throttle valve sticking or if allocation of the throttle potentiometer signals is undefined.
Replacement of electric throttle valve

If an electric throttle valve is replaced on a vehicle, the limit stops of the throttle valve must be re-learned. For this purpose, the electric throttle valve is activated for approx. 30 seconds after “ignition ON”.
The maximum opening of the throttle valve while learning the positions is 25 %.

Several interesting items.

One is the 'changeover' and 'selection of correct pot'. This is NOT how ME7 works. Seem to me the lawyers got involved in the later ME7 logic, cuz with those cars, the logic is "If anything seems FORKED UP at ALL, then FAILSAFE AND DO NOT LET CAR DRIVE!!!!". To be fair, probably being true DBW vs semi-DBW w/ a cable is the difference... with the semi-DBW MDK most likely the mechanical bits are still working fine, with true DBW the engine has no idea if you're in a Toyota situation, about to accelerate through a brick wall, even though the pots are reading "10% throttle", so it has to be extra paranoid.

The other is that the adaptation cycle only goes to 25% throttle. So the idea of using the auto adaptation to cycle the plate isn't very effective, which is why full WOT stomping the pedal is probably the best 'get yerself unstuck for now' approach.

Also, looking at the wiring diagram, my neato dual pot testing trick won't work, you'd need to apply power and ground to the units, then measure voltage across the 2 wipers. If any voltage at all develops across them as you sweep the plate, then they aren't in sync. Maybe you can do that in the car, I don't know - if the DME powers both sets of pots up at ignition-on before start then you could. Throw DC voltmeter on pins 3&5 (and later, on 6&8) and check for a voltage there as the throttle is swept. Any amount of non-zero voltage indicates the pots are not perfectly identical at that point. I'm sure there's some allowed margin of error...

[JimLev]

Yes, title is bad but I'm not sure how to edit after the thread receives replies. Can I do that?

No, but I can.
I tried to PM you to see what you would like the title changed to however it looks like you have PM's turned off.
Let me know and I'll make the change.

[philly98540]

Was updating title as Jim posted. Look ok.

[pleiades]

No, but I can.
I tried to PM you to see what you would like the title changed to however it looks like you have PM's turned off.
Let me know and I'll make the change.

Thanks Jim, that may attract a few more members to add to this already humongous amount of useful info I'm poring over.

To all of you, I really am thankful that you took the time to post. I'll be going over this stuff for days before I can actually try any more diagnostic steps.

As to why I wanted to or expected that I could drive the shaft out, it's simply because I saw no other way to get into the insides of the pot casings and see if the tracks were scored or torched or otherwise interrupted. Now I can see that may have been a sorely mistaken assumption, so I'm not going to pursue it.

Instead, for now, I will go get the Deoxit spray from Guitar Center, pore over the pin diagrams for the MDK and engine harness, and try to find if the fault(s) are something easily induced by the contraction from low morning temps (when both engine failsafes occurred, at cold start).

When I used my DMM to watch the range of resistance readings on the MDK connector socket pins, I didn't see any skips or interruptions in continuity as I slowly turned the sprung cable wheel. But then, my eyes are not as sensitive as the DME.

effduration, those links are appreciated. I had been through most of them already (except the second in your list) but hadn't saved any.

Aussie528iT, I'll have to learn what each of the pins on the MDK socket are meant for, and will try my resistance readings again to see if I can match what you got.

GG, I'm just going to spray Deoxit into the pot casings. They have small holes (well the one on the servo side does) that a spray can injector straw will fit through. No sense trying to dismantle any further, but I still would like to get the security nut off the cable-guide side and try to remove that cover and see what's in there.

About the only info I can add today is that the two security nuts appear to be M8 x 1.0 threaded. I plan to replace them and add a drop of loctite, but not sure whether I'll re-use this MDK or not. Probably it will sit here as a spare because I purchased another one used that I plan to install.

Anyone that sees this thread, please feel free to add any extra info you have. Seeing the other posts, it's apparent to me that these hybrid MDKs and their harnesses are one of the more-expensive gotchas waiting for M52TU car owners.

[pleiades]

Here are a few pics, FWIW .... (after I had removed the servo-side cover, coil, and magnet). The black plastic cover is held to the body proper by several tabs. I was worried about prying old ABS too much, so I used multiple small Wiha screwdrivers and picks inserted underneath the edges of these tab locations to carefully get the cover off. Re-installation should be much easier as it simply slides and snaps back over the tabs.

DSC_5884.jpg

The security nut on the cable-guide side of the shaft. I've already removed the six small torx screws around the edges (they're very lightly torqued on). I'll be trying to remove this side later because I want to see and hopefully clean the pot casing underneath.


DSC_5883.jpg

The heavy coil atop the magnet. Those torx screws are long and very tight. I had to use a socket adapter and wrench. I just didn't have the muscle to loosen them with a standard driver.



DSC_5881.jpg

The magnet still mounted on the shaft. The security nut is on loosely. I had already removed it with a combination of redneck trauma (chisel punch) and finally a 13 mm socket pressed down tight (this I should have tried first). The shaft and magnet hole are flattened on two opposing sides. The range of motion is the same as the shaft, about 90 degrees. No spinning motors in here.



DSC_5877.jpg

The pot casing attached to the shaft with a brass sleeve. It has some holes that would allow a spray can injector straw in to drench the tracks with contact cleaner (my next and probably last step).

This also shows the backside of the connector socket. That yellow plastic piece has a tab that ensures you have it properly aligned upon insertion into the black cover, and four prongs on the rear that slip into four corresponding holes in the aluminum body.

I tested the socket and wiring underneath the lower side of the pot casing for continuity, all "good."

I had also removed the butterfly plate, on the expectation I'd be driving the shaft out, but decided I won't go there as it will probably do irreversible damage. The two screws on the plate (not shown) were staked at their tips, presumably to prevent them from being sucked into a cylinder intake port if they loosened themselves over time.

[geargrinder]

Are you sure the pot is pressed on via the brass sleeve? Really looks like the white housing snaps into the metal case... Would be great if that would clip out and then the pot would slide off the shaft...

[pleiades]

Are you sure the pot is pressed on via the brass sleeve? Really looks like the white housing snaps into the metal case... Would be great if that would clip out and then the pot would slide off the shaft...

Mmm, that was my initial thought when I got the magnet off, but that white plastic ring isn't even touching the part of the pot casing that rotates with the shaft. It is indeed clipped into the two sides of the aluminum housing and the base is sandwiched between the lower, stationary pot half and the plug for the wiring harness. I unclipped it from the sides easily enough but the wiring plug is really in there tight and I'm afraid to force that out, being plastic and as old as it is.

[Aussie528iT]

Great pics Pleiades.
I have been looking for pics of the internals without success.
Are the pics of the first yellow label version or the later blue label version throttle body?
Does anybody know exactly what the difference is?
The BMW SI just says to replace the early yellow label throttle body with the later blue label version for plausibility errors but doesn't give any info about the difference.

Regards

[pleiades]

Ron, those are of the original "failed" yellow-label TB on my car. I have the used blue-label version in-hand now but am not planning to dissect it (yet).

Apropos of maybe nothing, with my digital caliper I tried measuring the distance from the tops of the outer ring of metal pins to the top edge of the connector socket (on both units) and -- while a bit shaky as the outer edge has lumps in it -- it seems that the pins in the yellow-label unit are in slightly deeper. I'll have to measure this again more carefully. Otherwise, superficially I see no difference....

Incidentally, for what it's worth, I re-measured resistance on the same pin pairs you listed (my TB's values are in parentheses). I think they may be indicative of why resetting adaptations is necessary when one throws a different TB in:

2 - 3 1740/970 ohms (1757/1023 ohms)
2 - 5 1920/1259 ohms (1802/1171 ohms)
1 - 6 1706/967 ohms (1791/1129 ohms)
1 - 8 1897/1252 ohms (1868/1189 ohms)