Yes indeed vac servo type. I do beleive it's under all the other ecu's in the engine bay ecu box (or it was in mine, passenger side front wing not behind the glovebox) It's a silver box, about the size of a cigarette packet. I am informed its a bit of a faff because all the other stuff is on top so many ecu's would have to be very carefully disturbed/lifted aside to get at the little blighter but thats what trained professionals are for :) I worked on the assumption that it would be a "shared" item over the models which is why I went looking for repair/problem for non A8 specific cruise problem. And I can happily report it fixed mine up a treat. It works first time everytime.

I think you're probably right, that thread was about the location in an A6 not an A8. The fix is the same though once you've got to it.
I'll see how mine behaves over the next few days.....

well the replacement box worked on mine :) assuming the solder repair works (apparently you can see the cracks on solder on the board?) and the module is the same then it should in theory work! i just chickened out and sourced a replacement rather than fiddle with invisible electronic magic I don't understand!

Well mine has stopped working again. :(
Time to investigate the control box methinks.

tinkering with elastictrickery fills me with dread *shudder* thats why I had someone play with such things. Moving ecu's and all those wires......that would give me sleepless nights! probably best seeing if you can find a replacement rather than discombobulating and attempting an internet solder repair on what is frankly a vital bit of kit that effectively makes the car drive itself! I distrust anything involving electronic repairs!

Each to their own. I'm totally happy messing with that. +++

Now, taking off a cylinder head is NOT my cup of tea at all.... :-(

+++
+1

Been there, done that


I am pretty much happy mess with everything. Also done electrical side on ABS pump which many would be afraid to touch once on C4 A6. Or taking airbags off

cylinder heads, now thats entirely more like it. More than happy to do those! can't beat a nice bit of tinkering with an engine's oily gubbins!

Been reading this with interest as i thought mine was a bit hit and miss until yesterday on whether it would work or not.

I think I've realised I've been trying to activate cruise incorrectly for the S8 based on what I've always done with the 2004 A6 we have! I usually flick the switch left to turn cruise on and then just hold it left to increase speed at the same time so I don't get a drop in road speed while it has a think.

It seems the S8 doesn't/won't activate like this, despite the stalk looking identical - if I use the push 'set' button on the end of the stalk having switched on cruise then it was reliably cutting in and I could then use the slider to increase speed, give or take the occasional cut out from the system.

Very rare I use cruise round these parts, but being on the M25 at 6am with lots of average speed checks and a couple of nice tunnels to run through needed a bit of self imposed restraint!!

Adrian

TBH I leave mine in the "on" position all the time, there's no reason I can think of to do otherwise.

But yes, push on the end to set a speed (or slow down if already set).
And flick slider outwards to resume or increase.

It's a rather odd setup compared to all the others I've met over the years, no symmetry to increase/decrease speed. :Confused:

Anyway, I'm beginning to think the problem with mine must be the control box....