S65/S85 throttle actuators - electrical failure SOLVED

I'm sure many of you are aware of, or experienced first hand, the common faults with the throttle actuators fitted to both of the above M3/M5 engines. I recently suffer this same failure and was determined not to path the stealers £800 each, especially when you really should be replacing both.

Many people are aware of the gear wearing issue and a couple of members have started to manufacture replacement gear sets which is awesome. However the secondary failure on quite a few actuators seems to be electrical, as many suspect, this being due to the backlash of the worn gears causing constant adjustment and overheating of the electrics. When this happens it seemed only a new replacement from BMW was the answer. Well I think I have cracked it.

My failure started when I was 60 miles from home so triggered I would try and get it home instead of waiting 3hrs for an AA low loader. Jerky throttle response followed by the eventual Christmas tree dashboard and error messages. The journey home was painful, but rather fun, as she hated cruising by WOT was fine . Having read the codes it registered P1628 being bank 1 throttle actuator. Once I was home, she was stuck permanently in limp mode and failed the pre-start actuator test. Following removal of both actuators I inspected and noted the gears were worn as many of us have come to find. Thinking this just meant I had to get the gears sorted I rotated the middle gear through 180degrees (less worn contact points) and refitted, hoping no codes would flag. No such luck, same code. I removed again and swapped the electrics over but left the main actuator bodies in their original positions - the only error then registered P161F being bank 2 throttle actuator, confirming the error had followed the board, not the gears. I removed both actuators for further inspection and found - you can see one of the MOSFET transistors is rather black:

https://www.dropbox.com/s/6ea8rpk62ujqblv/Photo%2008-12-2014%2019%2001%2056.jpg?dl=0

I then removed the blown Fet using an iron and de-older braid:

https://www.dropbox.com/s/n0jfuq79kd8dj1k/Photo%2008-12-2014%2022%2023%2043.jpg?dl=0

Following lots of investigation I located a replacement source from the states, this is the part - each board has 5, so just I case the others were fried but I bought spares, 15 in total ( they cost £2 each inc postage):

https://www.dropbox.com/s/tez8wix9xbjwqji/Photo%2008-12-2014%2022%2034%2033.jpg?dl=0
https://www.dropbox.com/s/1snj7mvju7zv5kt/Photo%2013-12-2014%2013%2004%2015.jpg?dl=0

And here is it fitted:
https://www.dropbox.com/s/49oac6syy0rxmda/Photo%2013-12-2014%2011%2009%2001.jpg?dl=0

Following refitting, she started first time, no error code on pre-check Annandale no error when running for 10 mins ( with tests at various throttle positions). As a side note, these engines sound epic without the plenum fitted!!!

Plan now will be to get the gears changed for new ones, but all in all a massive result I feel. 2 new, 'improved actuators' for under half the price of 1 new one. RESULT.

What a great job tracking down and verifying the problem. This is something that perhaps a vendor could take up as a repair service and obviate the need for expensive OEM replacements.

Very impressive! I applaud your patience and technical skill.

Good job man. I will be waiting your feedback about the worn gears. Let us know if you find replacement gears

Bimmer-M3 wrote

Good job man. I will be waiting your feedback about the worn gears. Let us know if you find replacement gears

That's the easy bit: already got them sourced, there's a couple of people around who can supply them ;-)

Good job matey. Can you post a link to where members can purchase the components and gears? Thanks.

I found the Fairchild MOSFETs at Digi-key.com (search on "HUFA76429D3ST_F085T-ND") on the Digi-key site. They are $1.44 each in single unit quantities.

I got them from mouser, they'recheaper ;-)

http://uk.mouser.com/Search/m_ProductDetail.aspx?Fairchild-Semiconductor%2fHUFA76429D3ST_F085%2f&qs=N%2f3wi2MvZWAJl6Ov0x0rig%3d%3d

0-60Motorsports wrote

Good job matey. Can you post a link to where members can purchase the components and gears? Thanks.

+1

Sean1933 wrote

That's the easy bit: already got them sourced, there's a couple of people around who can supply them ;-)

how can I get the gears? from which shop did you get them?

Nice work!

Bimmer-M3 wrote

how can I get the gears? from which shop did you get them?

The gears are a custom job (£200/$300 per actuator) from a specialist - cost is quite high due to the amount of labour involved and the materials being rather specialist due to high wear rates of these items - last thing any of us want is to have to replace the gears again in another 40k-60k miles. Will speak to him about giving out his details/getting a batch run done to try and reduce cost.

Thank you and great job in finding a solution. Too bad I replace both of my actuators. I will open mine up and see if they are in the same condition with a flown MOSFET.

I guess it will be good to have 2 on repair if the replacements fails.

Here are some pics of my faulty actuators. DOSFET are not melted but shows signs of discoloration i'm guessing due to heat.

It would be great if others would post pic to see if theirs are in the same condition as Sean1933.



Both actuator looks like this inside....shavings but not too bad. It looks fine to me.


Actuator #2 on the left and #1 on the right





Actuator #2
Slight hint of discoloration


Actuator #1
Clear discoloration

To check the gears you need to pull out the middle gear and look at the small one on the other side - I bet it has grey/black discolouration. Main gear that wears is the black half gear on the right, when you have removed the gear, look about 1cm in, the teeth are almost certainly going to be worn (I'm guessing that is where the throttle is @ idle and cruise.

From the photos the Fet in actuator 1 has clearly blown, it's not so clear in Actuator 2 - did that one throw error codes too?

More pics...
The wear really doesn't look bad at all.

Looks like the components are resin coated to keep out moisture? Can that be easily redone on your replaced one?

Sean1933 wrote

To check the gears you need to pull out the middle gear and look at the small one on the other side - I bet it has grey/black discolouration. Main gear that wears is the black half gear on the right, when you have removed the gear, look about 1cm in, the teeth are almost certainly going to be worn (I'm guessing that is where the throttle is @ idle and cruise.

From the photos the Fet in actuator 1 has clearly blown, it's not so clear in Actuator 2 - did that one throw error codes too?

I had codes for both 1 and 2. I replace #1 first and the car ran for 200 mile then the limp mode came back. It was off and on for a while...limp mode did not come on while driving. I recently changed out #2.
#2 actuator was not marked Siemens and it could have been made by a different manufacturer. production date was 2014.

What i'm going to do is replace the Fet and use them for backup. I hope my replacements holds up?

These gears should have been made out of metal.

chadwick wrote

Looks like the components are resin coated to keep out moisture? Can that be easily redone on your replaced one?

Yes. It's called conformal coating. With small repairs, you can touch up by hand using a brush applicator. Or spray the coating on from an aerosol can. Common brands are Tech Spray, Chemtronics, and Humiseal.

Flea7 wrote

More pics...
The wear really doesn't look bad

Have a look at the 7th gap from the left of that first photo (black half gear), that wear in particular will be causing massive backlash - causing constant gear adjustment and the Fet to overheat.

Flea7 wrote

These gears should have been made out of metal.

Problem with metal is they can be noisy, cause static and metal filings as they wear...not good with a circuit nearby!

Sean1933 wrote

Have a look at the 7th gap from the left of that first photo (black half gear), that wear in particular will be causing massive backlash - causing constant gear adjustment and the Fet to overheat.



Problem with metal is they can be noisy, cause static and metal filings as they wear...not good with a circuit nearby!

Thank for the feedback Sean1933. I would be interested in the custom gearing was well. I know there has been a couple of threads with this subject. Let us know if a group buy is an option.