speed sensitivity (servotronic) - The Unofficial BMW M5 Messageboard (m5board.com)

1day · 23rd October 2009, 14:44

thinking that my servotronic system is only working intermittently, so wondering what it actually affects...

I know I have speed sensitive wipers and servotronic steering... but I also noticed the other day that my car stereo (original hifi system - 10 speaker becker tuner, headunit, amp etc) goes up in volume automatically @ 100kph. At first I thought I was going mad, but then I tested it and it does happen.

can anybody confirm that this is a part of the servotronic system - or is it just part of the stereo...

and I wonder what else could be servotronic controlled, or take a feed from the servotronic system? any ideas?

hertfordshire1 · 23rd October 2009, 15:56

if your steering goes really really light all the time, then thats a sign the servotronic is having issues.

mine would start firm, then get lighter during my journey...

travelling at speed with the steering really light is not a pleasant one...

As for what else is servo controlled, no idea i'm affraid.

Steve

Alan Archer · 23rd October 2009, 21:10

Firstly, does your car have servotronic fitted ?
A check of the build sheet will tell you unless of course you have nurburgring suspension
with which it came standard.

It only has two modes & the switch over occurs just above parking speed.
Assistance is raised at walking pace & reduced at speed to improve feel.

The servotronic unit takes a speed input to determine setting just as the car audio
wiring provides a speed signal wire for volume control.

Hope that all makes sense...

Regards,

Alan.

richardbaxter · 24th October 2009, 02:26

Quote:

Originally Posted by Alan Archer

Firstly, does your car have servotronic fitted ?
A check of the build sheet will tell you unless of course you have nurburgring suspension
with which it came standard.

It only has two modes & the switch over occurs just above parking speed.
Assistance is raised at walking pace & reduced at speed to improve feel.

The servotronic unit takes a speed input to determine setting just as the car audio
wiring provides a speed signal wire for volume control.

Hope that all makes sense...

Regards,

Alan.

Alan

I returned from a very fast 120 mile journey last weekend, during which my instruments panel went psychotic needles of all instruments flashing back and forth, the mileage panel lost all data and showed up as brilliant screen. After I finished the journey I had to go out again for a short run and the steering felt very light almost over servoed do you think the two incidents are related?

1day · 24th October 2009, 11:27

Quote:

Originally Posted by Alan Archer

Firstly, does your car have servotronic fitted ? A check of the build sheet will tell you unless of course you have nurburgring suspension with which it came standard.

yes it has servotronic (Faz told me) and no EDC as it's a 3.6.

There is NO build sheet for my car (it's a South African assembled car) and despite many communications with various bits of BMW no build sheet can be found.

Quote:

Originally Posted by Alan Archer

It only has two modes & the switch over occurs just above parking speed.
Assistance is raised at walking pace & reduced at speed to improve feel.

The servotronic unit takes a speed input to determine setting just as the car audio
wiring provides a speed signal wire for volume control.

so the servotronic is independent (sort of), ie, it is sent a speed signal - by what I wonder? also, wonder how I check operation of the device that sends the signal...

I'm pretty sure it's operating intermittently, the stereo volume speed adjustment definitely doesn't happen all the time, so if thats feeding from the same signal then that would explain a lot...

also just thought - the drivers side windscreen wiper doesn't clear well when it's cold, which is the speed / pressure mechanism, I wonder if this is also driven by the same speed signal?

further complicated by cruise control I suppose.

and finally - read the instrument cluster repair page (posted on RichardBaxters thread re cluster failure) and it's starts with this sentence "instrument cluster started to fail by having the fuel, temperature, and lower digital readouts not working during the first 20 minutes of driving or until it warmed up" - I've had no problems this summer, but, when the weather turned colder recently the problems all came back...

1day · 24th October 2009, 13:26

from the service manual...

I understand the theory of this about 25% :-( - but sounds like three speed settings (parking, medium and highway speeds), which are sent to the pressure regulation ECU as pulses from the speedo.

So, i think checking the pulses (somehow) is required, but, thats not going to be easy as it will need to be moving to establish this.

I thin it might be a bad earth on the ECU - just a gut feeling but....

1day · 30th October 2009, 12:39

well, as the outer wing near the ECU look like this, and the inner wing / sill is apparently just as bad, I'm not surprised that earth faults exist....