S65/S85 throttle actuators - electrical failure SOLVED

meyergru wrote

Is any of you guys aware of the real cause of the problem? It's the lubrication of the throttle actuators, period.

The causality is as this:

1. The throttle actuators are on top of the engine, right under the airbox. They are open to any kind of dust and thus the lubrication dries out. That causes it to become stiff.

2. This in turn poses greater stress on the gears that are inside the housing of the TAs, eventually causing wear in them which in turn causes even more stiffness of the motion.

3. Eventually, the greater force causes a larger current in the actuator motors, which in turn burn out the FETs in the control unit.


If you think about this causality, you will find that swapping a failed FET will only fix the symptom, but not the cause. Same is true for swapping out the gears. The only true remedy for this matter is to lubricate the actuators before any stiffness has a chance to occur. And to repeat that on a regular basis.

I lubricated my actuators at ~25000 miles (4 years) and they already squeaked on manupulation - I was glad that it was not too late. So even if you have or had this problem: lubricate or else it will most surely re-occur!

Here are (german) instructions with a picture of the area in question. You can see the rod bearings in it. Alas, they are hard to reach, which may be the reason why the BMW maintenance instructions do not cover their lubrication.

Hot damn, that makes a whole lot of sense...I hadn't read about that yet...Thanks for dropping some knowledge on us I am sure mine have never been lubricated...time to add something else to the list heh. What did you use to lube them?

I suppose all the people just replacing the TAs should see less mileage before a fault on the second set of TAs.

Which points do you lube? I currently am using dry teflon spray on the linkages but i still get squeaks

here is the FET P/N from a couple sites
http://www.digikey.com/product-detail/en/fairchild-semiconductor/HUFA76429D3ST_F085/HUFA76429D3ST_F085CT-ND/4552481

http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/HUFA76429D3ST_F085/?qs=%2fha2pyFaduiOkCDapi%2fKsaAxDfuP4jPxLolB1WNeeSHgV7INTXL15cG6TxodtuX5

I would recommend finding a friend with a board preheater. It's kind of like a stove for a PCB. It really helps to melt the solder under the FETs.

kb9uwu wrote

time warp!

it's groundhog day!

meyergru wrote

Is any of you guys aware of the real cause of the problem? It's the lubrication of the throttle actuators, period.

The causality is as this:

1. The throttle actuators are on top of the engine, right under the airbox. They are open to any kind of dust and thus the lubrication dries out. That causes it to become stiff.

2. This in turn poses greater stress on the gears that are inside the housing of the TAs, eventually causing wear in them which in turn causes even more stiffness of the motion.

3. Eventually, the greater force causes a larger current in the actuator motors, which in turn burn out the FETs in the control unit.


If you think about this causality, you will find that swapping a failed FET will only fix the symptom, but not the cause. Same is true for swapping out the gears. The only true remedy for this matter is to lubricate the actuators before any stiffness has a chance to occur. And to repeat that on a regular basis.

I lubricated my actuators at ~25000 miles (4 years) and they already squeaked on manupulation - I was glad that it was not too late. So even if you have or had this problem: lubricate or else it will most surely re-occur!

Here are (german) instructions with a picture of the area in question. You can see the rod bearings in it. Alas, they are hard to reach, which may be the reason why the BMW maintenance instructions do not cover their lubrication.

That is one theory. But lubrication of ITB linkage was not an issue for other motor actuators like S62 V8s. The linkages on my 08M3 moved fine at 65k and 7 years. I did lube them but could feel no difference in actuation effort after. The ITB are necessarily spring loaded so some effort is required.

I am not comvinced lubing your 4 year old linkage at 25k miles proves lubed linkages will prevent actuator failure. If yours were 8 years old and had 100k+ miles on them, then I would agree they seem to be lasting longer than average and that lubing them could be the reason. But yours seem too young and low mileage to fail anyway, whether lubed or not and the future seems like speculation.

judging from this thread http://www.m3post.com/forums/showthread.php?t=1234084


there is a guy with 70k miles and original TAs who regularly cleans his throttle actuator linkages with soapy spray bottle and a light pressure washer and then compressed air.

Apparently, the bearings are sealed so it's more about cleaning them then actually being able to lube them.

3M 08897 is the preferred "lubricant" apparently but it's really just operating as a spray cleaner

pbonsalb wrote

That is one theory. But lubrication of ITB linkage was not an issue for other motor actuators like S62 V8s. The linkages on my 08M3 moved fine at 65k and 7 years. I did lube them but could feel no difference in actuation effort after. The ITB are necessarily spring loaded so some effort is required.

I am not comvinced lubing your 4 year old linkage at 25k miles proves lubed linkages will prevent actuator failure. If yours were 8 years old and had 100k+ miles on them, then I would agree they seem to be lasting longer than average and that lubing them could be the reason. But yours seem too young and low mileage to fail anyway, whether lubed or not and the future seems like speculation.

There have been many failures usually at 40-60' miles, and as I said, this also depends on your climate and how much dust is in the air. When I look at images of cars at 50' miles here in Germany, I can see the dust buildup and near the gaps you can see the oil being drawn out by that.

Mine was not as dusty as many pictures I have seen, but as I said, it squeaked already and manipulating it was much easier after lubrication.
Your car may be O.K. at even more miles, but I won't take any chances.

BTW: These are the areas to lube - I used WD40, because it is not so much about the lubing, but getting the dust out of the gaps:



Matter-of-fact, theorizing about increased actuation because of rough idle turns out to point into the wrong direction: Actually, I believe that the stiffness of the actuation causes cog wear in the area that is passed most often (low RPM) and thus it is most stiff just there. So, in order to keep idle RPMs steady, the control unit has to use more force in regulation, which causes an overshoot once it is applied. It is not rough idle causing the wear, it's just the other way round.

I used white Lightning clean streak then hit all the linkages with the aforementioned 3m dry silicone lube and the squeaks definitely stopped. This combo also leaves no residue to attract additional dust/dirt which is a major plus

Forgive me if this has been beaten to death. I just received a throttle monitor bank 1 fault 2b25. Anyone have luck changing out the gears soon after receiving faults and staying in the clear thereafter?

Sweetchuck wrote

Forgive me if this has been beaten to death. I just received a throttle monitor bank 1 fault 2b25. Anyone have luck changing out the gears soon after receiving faults and staying in the clear thereafter?

There is a guy on the M5 boards that even after getting a TA code, he replaced the gears with brass and delrin versions that he had a machine shop make for $700 (gearsmade.com) and 2 years later still hadn't seen a code again. But there has been at least one person who even preventatively replaced the gears with the non metal odometer gears set ($225) before any TA codes showed up and still got a TA code a year later.....so in conclusion it's a crapshoot. I have been digging into this issue and if you already have a code you probably might as well suck it up and buy a new TA. If you only seen the code once and you didn't drive it much after the code appeared and you are feeling lucky, you can try replacing the gears. There are guys who have been working on it for around 3 years on and off that still haven't pinpointed the root cause. I tend to lean towards the linkages stiffening up and the extra force required to drive them kills the gears and then the boards but who really knows.

I did the gears preventatively and I am going to try a fix the circuit board when mine goes but just because it's kinda interesting to me. But I am a board designer and I have all the soldering tools and even professional solder tech to help me out. I identified most of the IC chips on the board already and even found the datasheet for the actuator which shows the pinout for the connector.

1 month ago I had problem with 1st bank TA. When I opened it, there was black FET, I changed it but it was only few days till error comes again. So I did change the gears in booth TA with the plastic gears set from ebay, changed 2 FETs, also lube the TB shafts and all the stuff there. Now It's working fine for almost one month, no errors...

igorossa wrote

1 month ago I had problem with 1st bank TA. When I opened it, there was black FET, I changed it but it was only few days till error comes again. So I did change the gears in booth TA with the plastic gears set from ebay, changed 2 FETs, also lube the TB shafts and all the stuff there. Now It's working fine for almost one month, no errors...

oh nice, that's encouraging at least, yea I think we might be slanted a little pessimistic around here cuz it's more likely to have people come back and post their experience when it doesn't work than when it does work. Good luck in any case, keep us updated :-)

This may save some time in trouble shooting / testing electronic issues in the board. Putting everything back together to start the car is not necessary! Simply connect the TA to the harness, dont even need to bolt it down. Turn on ignition by pressing start button twice without foot on clutch or brake pedal. If the board is ok the actuator arm will twitch back and forth once. If it doesn't, the board is toast. I plan to do this for each transistor replacement.

svinfinity wrote

Which points do you lube? I currently am using dry teflon spray on the linkages but i still get squeaks

I used the mentioned 3M spray on each throttle body spring also, that is where my squeeking was coming from...

fasternfaster wrote

This may save some time in trouble shooting / testing electronic issues in the board. Putting everything back together to start the car is not necessary! Simply connect the TA to the harness, dont even need to bolt it down. Turn on ignition by pressing start button twice without foot on clutch or brake pedal. If the board is ok the actuator arm will twitch back and forth once. If it doesn't, the board is toast. I plan to do this for each transistor replacement.

I have had them twitch but that is not enough to know they are good. One may function fine briefly and then fall behind its counterpart in actuation and throw a code.

Here's a FYI for anyone looking to trying to repair their throttle actuator's circuit board. In the throttle actuator DIY thread, I posted a pretty extensive list of which ICs can be swapped on the board with links to parts on digikey or mouser.

http://www.m3post.com/forums/showpost.php?p=20299053&postcount=582

So I have done the gears and the mofset's on both actuators and the initially faulty actuator still throwing codes...When starting the car it's hit or miss. 1/6 times of starting the car it seems to be without fault but the other times it's comes on from start of after 5 mins of idling/driving. From a visual inspection of the rest of the board I have notice a difference between the bank 1 and bank 2. I have noticed little blemish in what I think might be some kind of resistor. I don't know if anyone could possible source this of if its even possible to swap but just courious before I but a new actuator. Thanks in advance for any incite.

Medi1985 wrote

From a visual inspection of the rest of the board I have notice a difference between the bank 1 and bank 2. I have noticed little blemish in what I think might be some kind of resistor. I don't know if anyone could possible source this of if its even possible to swap but just courious before I but a new actuator. Thanks in advance for any incite.

These cylindrical-package parts are not difficult to replace if you have a basic surface mount soldering station. The damage is to the metal end cap (or more specifically the solder tinning of the end cap) and should not affect performance of the part. The metal ends merely allow the part to be soldered to the board, and as long as the end cap has not fractured away from the body of the part, it should be fine. In your photo the damage looks superficial. Something else may be faulty such as the motor getting weak/slow/intermittent.

Have you swapped the circuit card to the other bank to see if it follows? that should tell you if the board or the motor is at fault. either way your running out of options and may be faced with buying a new one soon.

i swapped gears and it held up for a month. just swapped mosfets and its back running again. next time i'll likely have to cave and throw down the $900 unless I trade the car in before then...

Going to try this out. Thank you to all in this thread who helped.

Reviving this thread to see if anyone has been able to find the FETs lately. All of the links in this thread as well as what I can find on Google are showing the part is discontinued and no longer being sold.

https://www.ebay.com/itm/5PCS-HUFA76429D3ST-MOSFET-N-CH-60V-20A-DPAK-76429-HUFA76429-/192129331828