Servotronic Steering Assist Curve

[aom7]

When I first got my car years ago, the servotronic module was out, so I just unplugged it. (It would cause erratic steering boost at various speeds). While it was very heavy at slow speeds (it didn't completely kill power assist, just brought it really down), I did appreciate how tight and heavy it felt at freeway speeds.

A year later, I replaced the module with a new one and didn't really like how "overboosted" it now felt, I didn't like how I could almost steer with my pinkie at all speeds and I somewhat regretted fixing it. However, when others drove it, they did struggle a lot to steer at slow speeds, so I reasoned it probably makes more sense to have it.

I almost thought to use an electronic relay wired to a switch that would "disconnect" the servotronic module, giving me that nice heavy feel I craved for when I wanted it. However, I read that after being disconnected a few times (3?) something is triggered which would require DIS to recode. So that would have been too much work.

I recent came across this post which states that the E38 and M5 steering racks are the only stock steering racks that come with programmable/adjustable Servotronic power assist levels using NCS expert to code it.

E39 M5 Steering Box Swap Custom Servotronic Assist Curve Coding (bimmerforums.com)

So I went into the GM3 module, changed the settings from 01 to 03 (each model probably has different curves) and OMG... the difference is night and day and WONDERFUL!

It now has heavier steering at slow speeds (though not as heavy as when the servotronic was unplugged) and most importantly, at ANY other speed, it's NOT overboosted. The steering is nicely/heavily weighted and TIGHT. At 60mph for instance, you can't really steer with your pinkie, the wheel is SOLID on center, you do need to have a hand or two on the wheel in order to turn it and the wheel itself is so much tighter on center. When exiting freeways and taking curvy off-ramps... the steering wheel is also tighter and much more pleasant, even allowing more feedback in a way.

I think THIS should have been the stock setting for the Sporty Shorty... leaving the more over-boosted levels to the non-Sport models! I love finding things like this that makes me fall in love with the car again! Makes me want to detail it this weekend,

[rslifkin]

The servotronic on mine was flaky when I bought it (only worked for a minute or 2 at startup and only sometimes). Then it died entirely. 2 years later, I haven't bothered fixing it. The steering is a bit heavy at low speeds with the summer tires on (255s on 18x9s), but nothing terrible (still much lighter than my Jeep). With the snow tires on, I don't even find it heavy at low speeds. And once you're moving, the steering is pretty good.

Good to know that if I ever decide to fix it that I can change the assist curve.

[aom7]

Yeah, looking back it wasn't all that bad, but was just difficult for some family to drive it like that. There are several other curves I could test out, but it just seemed like this one (3) hit the sweet spot.

[Capt'n]

If a sudden entry, caused by a failure with your servotronic, appears about 30 times in your GM3s fault memory, the servotronic is forced to be shut down. That's when you feel like you're driving a truck at slow speeds. You could try to control the servo valve/converter and apply some voltage via INPA. If it's still working, you should feel a difference for a couple seconds, depending on the value you've typed in. That worked for me, after my servotronic happened to stop working without putting any entries in the fault memory of the GM3. Usually the converter (who is mainly the reason for your servotronic not working properly) is dead, if you feel the servotronic staying heavy after a few yards and that's when it usually starts to put sudden entries into the fault memory. Ignoring a faulty converter for too long can actually cause the servotronic section on the GM3 to be burned due to too much voltage being put in by the faulty converter. So, if you decide to replace your servo valve/converter keep in mind, that your GM3 could be faulty too, causing the new valve to not work properly.
Even if we drive heavy cars, the servotronic should make it that easy to steer your car with two fingers at parking speed.

[aom7]

That sounds correct, 30 times was the number. I can also confirm that the servotronic and cables were hot, when I initially decided not to replace the servotronic, I just unplugged it. That seemed to keep the wiring (and I guess GM3) cool.

Overall, it's better to have the servotronic working, but adjusting the curve helped a lot.

[chemmech]

gm3 servotronics circuits have type power mosfets chip module (pwm mode servotronics servo valve control) that have over current, short circuit and back emf over volt protection not easily burned out if the gm3 module is maintained properly very high tech stuff etc. some of the same stuff in the washer motor circuits which has short circuit protection etc.

[TOTAL HATE]

Hello aom7
im having a struggle to comprehend this topic
when you changed that setting from the GM3 module, you changed it using ncs expert right?
im having a problem that the steering is too light, after a bad servotronic valve made a resistor inside the GM3 module explode, I changed the resistor, now I have the servotronic working again but it’s too light at high speed and too light até low speeds, so I want to recode this module with that settings, can you explain to me better how you did it?

[aom7]

Hello aom7
im having a struggle to comprehend this topic
when you changed that setting from the GM3 module, you changed it using ncs expert right?
im having a problem that the steering is too light, after a bad servotronic valve made a resistor inside the GM3 module explode, I changed the resistor, now I have the servotronic working again but it’s too light at high speed and too light até low speeds, so I want to recode this module with that settings, can you explain to me better how you did it?

Hi, I'm so sorry, it's been so long since I've used NCS I can't recall at all how I did it. I can guess it was something involving going into the GM3 module, finding the setting for the Servotronic boost (it might have been in German) which only has those 3 settings and changing it then saving it. However, I didn't need to make any adjustments to the default value when I swapped in the new servotronic. So I wonder if you existing Servotronic got messed up after the GM3 resistor failed? So perhaps that needs to be changed too? Then again if something failed within the GM3, I guess it's possible the settings got changed. If you want, you can try to post some pics of the NCS expert screens and maybe I can remember or someone else can advise?

[TOTAL HATE]

- - - Updated - - -

Hi, I'm so sorry, it's been so long since I've used NCS I can't recall at all how I did it. I can guess it was something involving going into the GM3 module, finding the setting for the Servotronic boost (it might have been in German) which only has those 3 settings and changing it then saving it. However, I didn't need to make any adjustments to the default value when I swapped in the new servotronic. So I wonder if you existing Servotronic got messed up after the GM3 resistor failed? So perhaps that needs to be changed too? Then again if something failed within the GM3, I guess it's possible the settings got changed. If you want, you can try to post some pics of the NCS expert screens and maybe I can remember or someone else can advise?

No problem!
my car has servotronic from factory, this all happened because i had to change the steering rack, the old one was leaking and i bought a used one, after i replaced it, my servotronic was not working, the steering was hard at low speeds, after googling i found that when the servotronic valve goes bad, it takes a lot of current and blows a resistor inside the gm3 module, i changed the valve and the resistor and got the servotronic working again, im assuming, as you said up there, when you disconect the valve "3" times something is triggered and require DIS to recode, what do you mean by this?
i haven't bought yet the inpa kan cable to see the DTCS, i wil buy tomorrow