1N3 Servotronic Behavior

[Sam_u]

Hi all!
I have a A4 Allroad B8 with 1N3 servotronic power steering. Steering is nice and light on below 20-25km/h but after that the steering turns quite stiff. There is significant "step" when going over that speed so the steering behavior change is not smooth. Car is new for me so I don't know if this is normal or not? Can the threshold speed be coded to be higher?

[DanielHamilton]

I have Servotronic and it doesn't behave like that. Are you sure it's based on speed and not RPM? Speed shouldn't affect the power steering at all, but RPM will change pump speed which could cause a pressure change if there's a stuck relief valve somewhere.

[Sam_u]

Ok thanks. So is it so that there might be some issue with the steering?

[Smac770]

Might be an issue with the N119 Servotronic valve or the control of it, or the rack itself. Have you scanned for codes to see if the J519 (09-central electrics) is saying anything?

https://www.audizine.com/forum/showt...119-code-02838

We discuss the electrical operation of the N119 by the J519 a bit in that thread. I'm sure there's a measuring value for the active N119 current value or voltage value. You might log that to see if there's a substantial transition from the control module's perspective. You might also have a problem with the J519, if it's encountered water. Or a wiring issue, where the high current at low speed overcomes the inline resistance fine, but as the J519 tries to reduce that gradually, the wire path resistance just becomes a dam and cuts the resulting current straight to not enough to actuate the valve.

Essentially the J519 applies more voltage to generate more current through the N119 to open/close it more (whichever the actual motion is) and get more boost through the rack. As you speed up, the J519 backs off the voltage/current, reducing the steering boost.

[Sam_u]

Thanks!
Is there a way to investigate whats wrong? I have a decent knowhow and lift in my use.

[Smac770]

Starting to get so fucking tired of this web site. Trashed my post yet again because it wanted to do that cloudflare crap. Not retyping all that.

N119 servotronic.png

J519 is 09-central electrics, N119 values are in blocks 046 and 047, you can get vehicle speed in block 020
vehicle speed in red on left axis, N119 duty cycle % in green on left axis, N119 current in blue on right axis
J519 does PWM of B+ to N119 to establish the necessary current flow to generate the desired boost modulation
more current for more boost at slow speeds; you see it transitions smoothly across the 25 kmh point