C4 UrS Servotronic Control Module info

[K7ERG]

Think I have a few of them somewhere in the lockup. If needed.

Craig

[ChrisAudi80]

Think I have a few of them somewhere in the lockup. If needed.

Craig

Thanks for the offer. I will try Pop's spare one first. Its a little closer

[popdemonic]

Sorry Chris,I was driving on Bang Bua Thong-SuphanBuri Road and hard rain is pouring.I could not even see the front car taillight with
max speed of wipers.

[ChrisAudi80]

Sorry Chris,I was driving on Bang Bua Thong-SuphanBuri Road and hard rain is pouring.I could not even see the front car taillight with
max speed of wipers.

Oh, hope you got home OK. It has been hot and dry here all day.

[ChrisAudi80]

Just to update:

I bought a 392 (4B0 907 307) relay off Ebay. USD34 shipped to TH.
Works like a charm.

[UrS4boy]

Seems OK.

Just posting back the two photos

The first side:



The other side

[UrS4boy]

Just to update: I bought a 392 (4B0 907 307) relay off Ebay. USD34 shipped to TH. Works like a charm.

Good news. Somebody on my home forum (quattroworld) tried a C5 Servotronic relay and found that it actually INCREASED the steering boost!! Oops. I don't recall which number it was.

[ChrisAudi80]

Good news. Somebody on my home forum (quattroworld) tried a C5 Servotronic relay and found that it actually INCREASED the steering boost!! Oops. I don't recall which number it was.

I have not had servotronic working for a long time, so could not say if it boost more.
Steering is very light when parking, but the boost is not so noticeable when driving.
It does need getting used to. Steering with one finger. Have to be careful not going full lock.

[diesel des]

so not all cars came from the factory with these?

[UrS4boy]

so not all cars came from the factory with these?

No. Many did but at some point it was dropped from the S2 line. All the NAmerican UrS4/S6s got it. But I have decoded build tags from UrS owners elsewhere, e.g. a RHD 94 UrS4 in New Zealand that did not have it. The common code for Servotronic steering is 1N3, Speed-related variable steering assist. Straight up, no variable power steering is 1N1.

[Tommy200rs]

German MTM had hack upgrade offering at least to Audi S2 that made the servotronic boost aid smaller at higher speeds.

[UrS4boy]

German MTM had hack upgrade offering at least to Audi S2 that made the servotronic boost aid smaller at higher speeds.

Okay. How about a link to more info on that?

[Tommy200rs]

I never had opportunity to open such control unit that had been modified. The basic functionality for V8 servotronic is described here: 119 selfstudy, table at page 15

https://www.google.fi/?gws_rd=ssl#q=selfstudyprogram+119+servotronic

It is about the "kennlinie" in page 15. Similarly that should be changed so that the disangement happens at prefered vehicle speed or the strength of the apply curve. The servo "boost" curve amplitudes (in mA) are modified in different servotronic ecu versions according to weight load in the front and prefered reaction to speed. I assume that at that time S2, S4 A100/A6 servotronic principle was like in V8 because the same solution design was copy pasted between different models in many cases. Strange that disengagement happens 180-200km/h, but not much earlier.

wires in page 18:
GND
+ power for ecu and optional lamp engagement in different versions
speed signal input (like the same signal for motor ecu and stock radio and electric diff ecu at rear)
modulator signal wires (2) to servotronic valve