Cruise control not working
 

The cruise control failure is often just an underused stalk control. They frequently spend years not being used, and they seem to corrode over slightly on the contacts.

You often find that if you simply slide the switch on top back and forwards for a minute with some vigour, and press the button in and out a good number of times, it will start working. If this fails, it may be time to change the stalk over.

On prefacelift cars, it could be a perished pipe as the cruise system is the older 'sucking' system where a pump sucks the throttle in as required to achieve the speed desired. (you can feel the throttle moving beneath your feet) There is a mechanical failsafe as the tube used for the throttle pulling is physically terminated at the brake pedal. When the brake pedal is pressed, a valve opens and the pressure in the pipe is lost preventing the cruise system from artificially accelerating the car.

If there are any leaks in this pipe system, it will never pressurise and cruise can never function.

This doesnt affect facelift cars as they have electronic throttles, and all the cruise system is built into the ECU - The cruise stalk and its wiring to the ECU is the only possible cause of failure.

The cruise in my 'facelift' car is u/s too!

I specifically asked the vendor if it was working and he assured me it was. Are there any 'on' lights associated with it. It seems totally dead.:eek:

There are no lights, and on a facelift car, the stalk is the only component to cruise, so you've nothing to loose thrashing the buttons about vigourously trying to clean up the contacts. Alternative is a replacement stalk....

Not sure how it feels in the facelift, but in mine, you feel the pedal 'tighten' when you engage cruise.

Sometimes drops out when I try to increase the speed on the stalk, but a minor niggle.

The prefacelift had a mechnical cruise that physically moved the throttle cable, so you will feel the pedal move. This is normal.

Post facelift, its drive by wire, there is no throttle cable, so the pedal wont show any feedback. The cruise function is built into the engine ECU.

Its quite common for cruise to drop out when trying to increase speed, I've noticed it on a few cars, so you're not alone....

That's exactly what mine does...i just end up turning the cruise on, off but never using the increase speed function - when i do, it stops the cruise altogether.

I can't get the cruise to work again unless i turn of the ignition and restart the car again. It was never an issue though - it just meant you needed to avoid increasing the cruise speed! +++

-Oli

Ian

Thanks! I rattled the ON/OFF switch and prodded the SET button furiously and, after a while, it started working!:)

I'll never use it, but you know how annoying it is to have something you know is u/s.

The 97 one is still u/s tho.:(

Oh yeah! I'm going to abuse my cruise control switches! :)

It either fixes them, or they get replaced, so as noted, no loss either way..

I suppose I could develop carpel tunnel however if I cycle the switches too much...:tuttut:

I had a selection of those odd symptoms a while back; replacing the cruise stalk fixed them all. +++

Would be very interested to see how you get the stalk apart, as I haven't been brave enough to try yet...

Zip

UPDATE: Went for a 20 mile drive, "massaging" the switches for both resume/set/on/off and it finally, at the end of the 20 miles, started to work!

Nice advice, I'd have cursed the dang thing for awhile longer, and replaced the switches eventually.

This "free" repair is much better all around.

Thanks for the advice.

I think this S8 sat around quite a bit, as the mileage is pretty low with less than 75,000 miles on it.

Me too, does anyone know how to replace or dismantle it?

Mine has started seriously playing up again. The other day it did work eventually after some "abuse" of the switches, but yesterday it just wasn't playing at all. :(

Also, does anyone know if there are any codes that might show up as a fault.

Mine is the PF version, so you do indeed feel the earth move (under the accelerator).

I'd suggest squirting some switch cleaner/ lubricant around/ into the offending areas then vigourously working the switches.....
Be careful not to spray all over the interior though, so hold a cloth/ rag around the stalk...

Well, as noted briefly in another thread, I've doused it in Isopropanol several times and worked the switches "vigorously". Nothing mucky came out though.
Been on a short slow test drive - about 20 minutes at 30/40mph - and it still wasn't working despite trying every few yards.

Then just short of home it suddenly engaged; I have no idea what was different. Just enough time to check that the increase speed switch worked before having to brake and turn off down my road.
(no opportunity to continue and test further due to roadworks with traffic lights)

So, none the wiser really. :Confused:

However, looking closely at the switch it appears that it "might" be possible to prise it open in situ without taking the stalk off (airbag out job methinks :( ) - anyone ever tried that or know if it's possible?

I had problems when I got my S8 in January. The issues boiled down to 2. Firstly, underuse made the switch temperamental and, secondly, my right foot. If I left my foot on the throttle for a nanosecond after pressing the CC engage switch it would not engage. The trick was to ensure you lifted your foot off in the nanosecond before you engaged.

The removal route is well covered in Audi pages (as you probably know):

http://www.audipages.com/Tech_Articl...chreplace.html

Ah, thanks for that useful "how to" link. +++
Mine's a late 98 so I do need to check the revision carefully!

As for "foot off first" I do that automatically, but I have found in the past that it wasn't strictly necessary.

Is there any way to tell, without dismantling, whether you have a RevC or RevN cruise stalk?
Looking at the AudiPages photo the cloth-wrapped cable seems to leave the back of the stalk in a different direction...
Down, forwards, up and across on C.
Up, forwards, down and across on N.

Edit: I can see mine leaves the back of the stalk, goes up, round a plastic lug and towards the driver, then down the drivers face of the stalk back and across into the cowling.
So, I guess it's an "N".......

Working again!
 

Well, I just went for a short drive and it's working perfectly! +++

Maybe it's due to all the cleaning and abuse I applied to the switch the other day.
Or maybe it's because I was very careful to "flex" the throttle and ensure it was completely released and I could feel speed dropping before pressing the engage button? :Confused:

Anyway back to being a relatively happy bunny. ;)
(just have the gearbox to really worry about now...... :( )

Mine (97 pf) stopped working last summer, worked ok and then after 10 mins would suddenly drop and no longer engage. Continued to do that for a week or 2 with me assuming the switch was being a bit iffy before packing in completely. No codes set (because as I discovered it just thinks it's turned off!) and all the mechanicals seemed to be fine. Long story short after a bit of internet research for cruise control problems turns out the controller (like the type fitted to mine) dies...... controller swapped and tada! cruise works first time everytime. There was a "how to" on taking that type of controller to pieces resoldering the dodgy connections (3 bits of the electronic dodads attached to the pcb break their solder joint and drop dead) to bring them back to life but frankly whilst I can wave a spanner if needs be, electronic whizz bangs are not my thing! Don't always assume the switch is the cause!!!

Where is the controller, easy to get out?
I don't mind taking electronics apart and resoldering etc. at all. +++
I've got the "old school" vacuum servo cruise which I presume is basically the same as yours, so if it plays up again I'd probably want to have a look at it.

Ah, think I've found it, behind the glovebox according to this thread:
http://forums.audiworld.com/showthread.php?t=2758040

The actual module 4D0907305 seems to be common to several Audi models, not just the A8.

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....

Odd how it always seems to be capacitors, had to replace 3 in my Pajero (Shogun) ECU, then from dead to running perfectly :)

with that, the goo drained out of them with the heat cycles & upset the pcb & legs, so had to be a little creative with the dremel, tinned copper wire & some good old fashioned leaded solder.... the ROHS compliant stuff is rubbish, just can't take the heat cycles & crack (which is why the nvidia GRAPHICS chipsets on laptops give up- so never let your teenagers use them on their beds - blocking the ventilation as well as clogging the heatsinks)

Not afraid to get oily & dirty, or burn my fingers with the Weller, Pace, or gas iron...

Curious to see how you get on with it HP

I don't find the cruise control operation especially intuative. Despite having had the car for 30 months and using the cruise quite often, I still find myself selecting increase speed rather than disengage!!! Which can lead to some interesting moments :)

I'd love my cruise control to work properly, but I have neither the time or money to replace the duff indicator stalk on mine.

Mine has a mind of its own, some days it will work others it wont. On the days it decides to work I can set the speed, however I cannot increase speed using the slider as operating this to the left disengages the cruise control. So I can set it and decrease speed and thats it.

Well, maybe it is the controller box, not the stalk? That's the way my thinking is going now.

This morning I went for a short drive - basically to fill up with petrol and a couple of other errands at the same time.
It was damp and quite chilly - 5C when I left home, 6C along the main road.

And it was working again, on the way there (possibly after a little initial hesitation) and after a 15-minute or so stop perfectly on the way back. :Confused:

Just need to find a dry day to get into the box with all the ECU's.... :(

More symptoms to support this view. On Sunday I started off on a trip (cold damp day) and it was working fine. However at one point it just disengaged, but a few seconds later I was able to re-engage it! I didn't touch the brake - honest!
Later on (after a stop) it just wasn't working at all. The stalk was "on" all the time (as it always is).

Well I've had the cover off the electronics box with the controllers in it. Perfectly dry inside and no signs of any ingress of anything non-human.

Cover was a bit tricky as some of the bolts were corroded into the sockets, but it's gone back on securely and still works!
There was a bit of accumulated crud down the inaccesible edge under the windscreen so I hoovered and scraped out as much of that as I could. The seals looked OK though.

However once inside I'm rather wary. The main ECU is obviously outboard with nothing under it. So I left that alone.

The gearbox ECU is inboard and held down by 2 bolts at the front edge. I undid those so I could take it out but there was only limited movement and what appeared to be a release lever for the cabling was blocked by a fuse carrier. It wasn't obvious how to get it fully out - can anyone explain in detail?

Under that there is at least one more ECU but I couldn't see any label on the visible one. Is that likely to be the Cruise Control or is there something else to get out first?.

Having looked online I can only find an illustration of a LHD system, and there the ECU's are mounted vertically so the cruise unit can be taken out easily. :(
There are no other units mentioned so I hope the one under the gearbox ECU is the cruise control.

Has anyone delved that far into the box who can advise? Ideally without having to unplug the other ECU's.

Well, as noted in another thread I obtained a replacement Cruise ECU and had it fitted by my local VAG independent (while in there for a gearbox fluid & filter change) and it now all works fine. +++

Apparently all the ECU's had to come out to get at it, it's right at the bottom, so I'm glad I left it to them.

Nice one, it's very satisfying having the cruise back on song! My spanner waver did say it was a pain to swap mine out because of the stuff that needed to be removed.....

My "spanner waver" charged me £56 (inc VAT) labour to fit and test mine. Not bad really.