S65/S85 throttle actuators - electrical failure SOLVED

[kb9uwu]

time warp!

[igorossa]

Just had the same problem with transistor.
All the day was fine, but after some stop for 10 mins car starts with some errors and only on 4 cyls... after connecting diagnostics it says throttle actuator... when pull airbox off, right throttle bodies was fully opened...
Removed the actuator and saw that:


then bought new transistor and replace...



Problem solved! )))

[kb9uwu]

it will be interesting to hear how long your fix lasts! please report back in a few weeks/months!

Others also did this only to have the TA fail again after a few starts/days/weeks

[Bartledoo]

Did anyone ever do this in combination with replacement gears? It seemed unclear whether the OP replaced the transistors and gears at the same time.

[drummer20]

Originally Posted by igorossa

Just had the same problem with transistor.
All the day was fine, but after some stop for 10 mins car starts with some errors and only on 4 cyls... after connecting diagnostics it says throttle actuator... when pull airbox off, right throttle bodies was fully opened...
)))

replacing the gears too from http://www.odometergears.com/product...+E92+06-13/160 it's actually pretty cheap considering you get gears to do both TAs.

I think from the thread history, if just the fet is replaced then the problem will reemerge i relatively short order....however, if you replace the gears, you might be the one to verify that changing both the gears and the fet is a solid and hella less expensive fix. I haven't seen the issue in my 2008 with 40k miles yet but I am seriously considering swapping the gears just to prevent stress on the electrical parts.

I have a master's degree in EE and I design h-bridge motor drives occasionally at work...my theory of what is happening is when the gears become worn, the control loop is constantly turning the FETS on and off to make small adjustments because it is sensing lots of small changes from the loose gears. That is only happening because there is play in the now worn gears. The period of max power dissipation of a FET is when it's being switched on or switched off so if it's being switched on and off way more often than it's designed to, it will overheat and fail.

The heat from the FETs is designed to flow into the board through the FET's thermal pad for heat sinking so it will raise the temperature of the components near the FET as well, causing secondary failures that will be time consuming to find. You would have to start removing resistors and capacitors and measuring their values and you wouldn't know what the correct values are.

[pbonsalb]

I believe people have tried doing both gears and FETs and still had failure. At one point odometer gears was going to include FETs with the gears.

Maybe if you caught the problem before you knew there was a problem, you could get more life out of the circuit board. A preventative maintenance FET replacement.

[drummer20]

Ah I see, I couldn't tell that anyone had tried both after a code is thrown yet.

Yea I was thinking it's kinda like a transmission fluid change, swapping the gears every so many miles to help prevent a more costly breakdown. If that FET is overheating then, it's internal junction temperature is exceeding 150C, then the parts nearby are probably degrading too. But if with new gears every 40k miles, the FET never overheats then maybe the PCB last much longer.

I hear ya though, it's speculation, it's a $225 plus a long saturday in the garage gamble.

[crypticc]

Originally Posted by conscom

Go to odometergears.com US$225 for 2 sets. You don't want to mate metal gears to plastic.

I thought brass + nylon was considered ideal and nylon+ nylon is bad?

[Theodore]

Originally Posted by drummer20

replacing the gears too from http://www.odometergears.com/product...+E92+06-13/160 it's actually pretty cheap considering you get gears to do both TAs.

I think from the thread history, if just the fet is replaced then the problem will reemerge i relatively short order....however, if you replace the gears, you might be the one to verify that changing both the gears and the fet is a solid and hella less expensive fix. I haven't seen the issue in my 2008 with 40k miles yet but I am seriously considering swapping the gears just to prevent stress on the electrical parts.

I have a master's degree in EE and I design h-bridge motor drives occasionally at work...my theory of what is happening is when the gears become worn, the control loop is constantly turning the FETS on and off to make small adjustments because it is sensing lots of small changes from the loose gears. That is only happening because there is play in the now worn gears. The period of max power dissipation of a FET is when it's being switched on or switched off so if it's being switched on and off way more often than it's designed to, it will overheat and fail.

The heat from the FETs is designed to flow into the board through the FET's thermal pad for heat sinking so it will raise the temperature of the components near the FET as well, causing secondary failures that will be time consuming to find. You would have to start removing resistors and capacitors and measuring their values and you wouldn't know what the correct values are.

Let me pose a similar, but slightly different theory to get your professional opinion, as an Electrical Engineer: What if another component of the engine's throttle system was causing unexpected idle fluctuations on a regular or semi-regular basis? Is it then possible "the control loop [might] constantly turn the FETS on and off to make small adjustments because it is sensing lots of small changes" as a result of a rough idle source (different from the worn throttle actuator gears)?

[Bartledoo]

Can we just tee off the A/C and run it through the housing to cool em off?...:-P

[igorossa]

Yeah, you right guys, it was just a few days when the FET blows again... looking for some solution with new gears. Don't want to replace plastic to plastic, want to make the metal (brass or alu) copy, for lifetime solution... will post an update when done...

[pbonsalb]

Originally Posted by Theodore

Let me pose a similar, but slightly different theory to get your professional opinion, as an Electrical Engineer: What if another component of the engine's throttle system was causing unexpected idle fluctuations on a regular or semi-regular basis? Is it then possible "the control loop [might] constantly turn the FETS on and off to make small adjustments because it is sensing lots of small changes" as a result of a rough idle source (different from the worn throttle actuator gears)?

That would be fine if the car had the same symptoms with the new actuator, but they dont. You are trying to find another problem that no one knows exists. That is hard. It is a possibility but seems remote. The actuator failure happens on S85 motors as well.

[pbonsalb]

Originally Posted by igorossa

Yeah, you right guys, it was just a few days when the FET blows again... looking for some solution with new gears. Don't want to replace plastic to plastic, want to make the metal (brass or alu) copy, for lifetime solution... will post an update when done...

Good luck and keep us posted. Someone in the UK sells expensive partially metal gears. But I would not bother with them. Circuit boards in the middle of V8 engines may need to be designed with greater durability.

Too bad you cant buy the boards for $100.

[igorossa]

Originally Posted by pbonsalb

Good luck and keep us posted. Someone in the UK sells expensive partially metal gears. But I would not bother with them. Circuit boards in the middle of V8 engines may need to be designed with greater durability.

Too bad you cant buy the boards for $100.

actually it was stupid idea to make 2 separate TA, which also has some troubles with... if you remember on S62 (M5) engine, there was only one and never has problems like that...

[pbonsalb]

Originally Posted by igorossa

actually it was stupid idea to make 2 separate TA, which also has some troubles with... if you remember on S62 (M5) engine, there was only one and never has problems like that...

I have read the S62 did not have issues with its single actuator for both banks. Don't know why two are required on the newer motors.

Some of these cars buck when cold. Maybe that jerkiness is hard on the plastic gears? Someone has posted about the possibility of the actuator wear being caused by another problem and at first I questioned whether there were any problems anyone knows of. I thought about it and the only thing I have experienced is that bucking when cold. Not sure whether all cars have the issue.

[igorossa]

Originally Posted by pbonsalb

I have read the S62 did not have issues with its single actuator for both banks. Don't know why two are required on the newer motors.

Some of these cars buck when cold. Maybe that jerkiness is hard on the plastic gears? Someone has posted about the possibility of the actuator wear being caused by another problem and at first I questioned whether there were any problems anyone knows of. I thought about it and the only thing I have experienced is that bucking when cold. Not sure whether all cars have the issue.

Just get answer from machine shop, so it will take to long time to build the gears from scratch... so ordered plastic set for 2 TA...
will post update when done...

[drummer20]

It's a good point that in normal use, the throttle would be responding to a lot of small adjustments info multitude of reasons so those FETs will be getting plenty of exercise in an hot ambient enivornment even in normal use. And then as others have said, if the gears get loose, the throttle might not ever get to where it wants to settle and the FETs might get even more exercise and then failure.

However that all doesn't really explain why changing both the gears and the FET(s) doesn't result in a long term fix though. A typical FET circuit is microcontroller-->FET Driver chip-->FETs. Not really that complicated. The microcontroller is going to be getting digital data from the gas pedal digitizer and the throttle position sensor and trying to make them line up by driving those plastic gears to where they should be with the FETs. If a new FET works for a bit, but a new FET and new gears don't fix it, maybe the motor that drives the gears is the culprit. As it ages, the motor draws more and more current to do it's job and overheats those FETs.

Any chance someone could pull a part number off that motor? Maybe could find it on digikey or mouser.com or a suitable replacement one for cheap

The other I should mention is that there's actually 4 FETs on that board that drive the negative and positive of the motor on that PCB. Might as well replace them all if you want to refresh the board as much as possible. Maybe one of the other FETs is degraded and it's not visible.

also my car has the bucking at cold, 6MT. I hate it, makes me look like I don't know how to drive heh. I can usually avoid it with plenty of gas pedal and easying the clutch out real slow.

[IIAp3x]

All this engineer, transistor, flux capacitor talk makes me want to just spend the $700 for the new actuator... Nuts and Bolts are my friends...

[drummer20]

I just found this on http://www.rebuild.org.uk/buy-replacement-kit/ haha

Basically This issue has already been run to ground.

start quote from site<


NOTE: 50% of the time worn gears cause the Mosfets to over work and burn out. It is strongly advised when you replace the gears you also change the 4 mosfets per actuator. NOTE: Its the 4 mosfets along the top of the board. ALSO if the fault remains with the board, we can change additional 2 IC's A voltage regulator and an EEPROM Memory chip. Changing gears and Mosfets will resolve 90% of faults and the other components will resolve 95% of faults. We can NOT repair faulty Microprocessors or motors and can not be responsible for these.

Important: These are surface mounted components need to be carefully removed. Ensuring the circuit board tracks, pads and surrounding plastic connectors are not damaged in this process.

>end quote from site

They don't give part numbers for the Voltage Regulator or the EEPROM but maybe you can see that on the board.


I also read that it helps to blow out the motor with compressed air, it releases a bunch of dust and should help too.

[meyergru]

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 manipulation - 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.

[igorossa]

So after all, decided to do full maintenance of TB, clean those and lubricate. Change TA gears and FETs...

[pbonsalb]

Originally Posted by drummer20

I just found this on http://www.rebuild.org.uk/buy-replacement-kit/ haha

Basically This issue has already been run to ground.

start quote from site<


NOTE: 50% of the time worn gears cause the Mosfets to over work and burn out. It is strongly advised when you replace the gears you also change the 4 mosfets per actuator. NOTE: Its the 4 mosfets along the top of the board. ALSO if the fault remains with the board, we can change additional 2 IC's A voltage regulator and an EEPROM Memory chip. Changing gears and Mosfets will resolve 90% of faults and the other components will resolve 95% of faults. We can NOT repair faulty Microprocessors or motors and can not be responsible for these.

Important: These are surface mounted components need to be carefully removed. Ensuring the circuit board tracks, pads and surrounding plastic connectors are not damaged in this process.

>end quote from site

They don't give part numbers for the Voltage Regulator or the EEPROM but maybe you can see that on the board.


I also read that it helps to blow out the motor with compressed air, it releases a bunch of dust and should help too.

Can one of you smart electronic guys post part numbers for digikey or mouser so us dumb guys can order? I can solder and desolder OK but would love to see a DIY.