I recently bought a secondhand A3 (from a NON-main dealer garage) but have had continual problems with cruise control.
Sometimes the cruise control will not 'engage' i.e. switch on and sometimes when it is on it will switch itself off. In either case once it's decided that it is not going to work it, I cannot re-engage it until I stop the car and switch off the ignition. It's an intermittent fault and there seems to be no common theme to being able to reproduce the fault e.g. it is just as likely to not work/switch off when driving along a smooth road as going over a bump.
I originally took it back to the garage I bought it from, who have done their best to resolve the problem; They changed the cruise control stalk on the steering column but this didn't fix it.They then decide it had to go to an Audi dealer for further investigation, who informed me they 'thought' it was a 'Control Column ECU'. Needless to say, when I picked the car up from the Audi garage and drove it home, the cruise control promptly failed.
It's been booked back into the Audi garage but this is now the 4th time it's been in (to a garage) and while it's cost me nothing for the 'repairs' so far, it's becoming a little frustrating and I'm not particularly confident in the garage's troubleshooting abilities (have the earths been checked ? etc etc).
I'm looking for some advice/information on how these cruise controls work (or better still if someone has had similar problems and how they resolved it). It's getting to the stage now where I want to fix it myself (although I'm going to continue to take it to the garage for the moment); I have the technical ability but just lack the specific technical knowledge.
So in summary :
1) Has anyone had a similar problem to mine ? If so, did you resolve it and how ?
2) Does anyone have any technical information on how the cruise control works ? (There's no Haynes manual available, nor Bentleys for this year of A3)
3) Are there any diagnostic codes related to the cruise control and would it be worth me getting my local garage to get a read out of these ? And are these codes any good for troubleshooting ?
4) I've manage to gather that the 'Steering Column ECU' (mentioned above) interfaces with the Engine ECU. Is this through a dedicated electrical connection or via a digital bus ? Could it be the Engine ECU at fault ?
5) If it is an earthing fault, does the earth for the cruise control share it with any-other service - for example on some old cars the indicators would share an earth with the headlights and if the earth was poor it would cause the headlights to alternate in brightness in sympathy with the indicators. Where are the earths for the cruise control ?
6) Any other advice anyone has is also welcome !
Thanks for reading my post.
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I would have the clutch 7 brake light switch operation checked out first as these are closley related to crusie control. They are adjustable but are very sensative & very problamatic. I wouldn't recommend trying to set them yourself. the switches are multifunction so don't asume if the brakelights are working that all is well.
is the vehicle still fitted with the original radio?
I Doc
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Faulty switch on the brake or clutch pedal. This can stop engagement and disengage at random. Post this on www.veaudiforum.co.uk Regards Peter
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Synchronous posting. Regards Peter
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The proper way to tackle this is via the fault codes which are fairly comprehensive in this area. I'm unaware of a "Steering column ECU" - the system is in fact dead simple as all VAG cars of this vintage are drive by wire and are designed for cruise. I had it retrospectively added to mine with complete success.
In the absence of fault codes, my first port of call would be the brake lamp switch - these are famed for their unreliability and any intermittency here will cause the vehicle to drop out of cruise. They are also dead cheap and can be fitted in about 2 minutes - just take advice on the correct fitting procedure to avoid breaking the new one.
659.
Synchronised again...
Edited by 659FBE on 28/12/2008 at 16:40
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Check the foot brake switch - if this is faulty then the ECU will cut out the cruise mode. The foot brake is a common fault on Golfs but usually flashes a light on the dash.
Also check the final clutch position sensor (when pedal fully out).
It is not an ECU fault as the ECU is common to the engine nor is it an earth fault.
I doubt there will be any ECU codes logged since the cruise mode sounds like it is being exited correctly.
Something to try - if the cruise will not engage then kick the footbrake and clutch fully in then try again. Also pull clutch pedal further out with your toe.
I may be something as simple as a new clutch cable has been fitted and the pedal is now in a different position.
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I've looked and checked (with a multimeter) the brake pedal switch myself, all seems ok. I've tried the pumping-of-the-brake pedal to no avail,and also pressing of the clutch. I'm not able to locate where the clutch switch is... it's not in a similar position as the brake switch on the brake pedal, although it is very awkward to see groveling right down there in the foot well.
To be honest I'm not convinced it's a switch. The only consistent thing is that the cruise control will work again after switching off the engine. Also, if it was an intermittent brake or clutch switch surely it would just sense this as a braking or gear change and dis-engage. Re-engagement would be possible after a few pumps of the pedal (assuming it's an intermittent electrical contact)... but it doesn't. I have to switch the engine off.
Thanks for your reply - much appreciated
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injection doc : It is fitted with the original radio.
Peter D: I've posted on that forum you mentioned and had a few replies and all say the clutch or brake switch.
659FBE : There truly is a 'Steering Column ECU'.. as odd and complicated as it sounds. I have gathered that the airbags, cruise control and indicator stalk (as well as a few other functions) go through this box (why oh why everything has to be so complicated !). I just don't know how 'Steering Column ECU' signals the engine ECU (for the cruise control).
vw fan: Where is the clutch switch located.. is it on the pedal ? (I'm having trouble finding it.. I might just need to jam myself a bit harder into the footwell to see it !). I'm not convinced it's a switch problem but as I've not been able to verify the integrity of the clutch switch I'm still open to the idea. I wouldn't categorically dismiss the engine ECU being OK.. even though it controls the engine it must have control of the inner workings of the cruise control.. (I'm assuming it's an electronic throttle)... but as I don't know how the system works I'm willing to admit I'm speculating here. Also, which (complicated) box of tricks brings on the cruise control light ?
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Cruise is already on most modern engines like my Passat. To enable cruise all I need to do is tick the box in the ECU (using the VW diagnostics port) which tells the ECU to enable cruise and also I need to fit the control stick on the column. The clutch and brake switches are already fitted. It is not a £170 option but about £5 in parts but the manufacturers charge a small fortune for something already fitted.
When the foot brake switch failed on my Golf the fault latched until the next off/on via the key. VW were forced to do a recall in the US for the Golf (Rabbit) due to the foot switch as it is deemed a safety feature but not here. £20 switch and £55 to reset the ECU fault code to stop flashing the light on the dash.
The point is that the clutch or brake sensor could be faulting the ECU and the ECU disables cruise until the next off/on.
I dont know where the clutch sensor is - possibly on the gearbox though.
It could be other things like faulty cable loom/connection etc to the brake/clutch switches but the brake switch failed on my Merc and Golf. My hunch (it is just that) is that the lack of lights on your dash points to clutch switch but take other advice before rushing ahead.
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vw fan:
I'll see if I can find the clutch switch. I can't get my head round how it could fault the ECU (unless the switch has an internal fault/breakage causing it to short to earth for example). I do think it's on the gearbox.. I don't see any wiring looms in the vicinity of the pedal.
My worst fear is that it is a loom problem.. that's going to be a pain to track down !
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The sensor on that car is not on the pedal but the other side of the bulkhead and the air cleaner needs to come out. However, if either of the switches were to blame then a Tech monitoring the live data with Vag-Com whilst you go for a run will identify the fault. Regards Peter
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Peter D:
Thanks for that info.. sounds like that one is best left to the garage (while the car's under warranty anyway !)
I've thought about buying one of those small code readers as no doubt if I go for a 10 minute drive with a technician it will work perfectly so if I get my own I could drive with it permanently plugged in.. would you have any recommendations as to what device to get ?
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Live data is not available on cheap code readers. Just tell the garage that you think it is the brake or clutch sensor and see what they can find. Also write to Audi UK and complain so the the fault is covered after the warranty runs out. Regards Peter
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