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Old 02-21-2011, 10:55 AM   #1
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Default ASR Light stays lit

But vag-com does not give any codes, happened about 120km ago.

Started when went to town, no harsh driving, got my things done and went back home, half a way, asr just lit up, no other lights, no abs no anything, got home, checked for codes but no success..

what can cause this ?

A8 2.8 128kw automatic front wheel drive 1995.

Thanks.
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Old 02-21-2011, 07:34 PM   #2
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In newer US model VW/Audi's with ASR, light staying on usually points to a failure in the elec module on the ABS hydraulic unit or a component electrically connected to it.
Wouldn't know what else to tell you if no codes?
Does the traction control seem to work now? ...try spinnin wheels in the snow or loose gravel? ABS braking working?
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Old 02-22-2011, 06:45 AM   #3
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ABS works perfectly, but asr doesent, on ice only 1 wheel spinning, if asr worked then other wheel started to spin to, as result braking that wheel what was spinning..
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Old 02-23-2011, 06:54 AM   #4
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Quote:
Originally Posted by RKsilver View Post
ABS works perfectly, but asr doesent, on ice only 1 wheel spinning, if asr worked then other wheel started to spin to, as result braking that wheel what was spinning..

Because of the year of your car and unknown OBD version, I don't know what (if any?) codes you should get. But does sound like something could be failed at the ABS hydraulic module(usually electrical in newer models) which controls wheel spin during ASR intervention.
There are many companies in the US and UK that specialize in testing and repairing the elec module on the unit...if that's your problem and not some other control component..like the ABS computer in the car, if your model has one, like newer models. On many cars , the elec module can be removed from the hydraulic unit, leaving the car drivable (without ABS functions)while it's being tested or repaired.
But again, without codes, these are just guesses and a place to start.
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Old 02-23-2011, 07:48 PM   #5
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Further on that - there's just a few differences between an ABS electro-hydraulic module and an ABS+TC electro-hydraulic module. Since your ABS works fine, that helps rule some things out.***

Internal electrohydraulic:
-------------------------------
ABS-only: 8 solenoids
ABS+TC (for pass cars with diagonal split braking systems): 12 solenoids - that's 2 extra solenoids per circuit to allow the unit to build/control brake pressure above the level of the master cylinder.

Normally a fault in one of these, such that it would disable the ASR system, would also generate a fault code. ABS is preserved as long as the 8 ABS solenoids are not affected.


External
-------------------------
Communication with the engine - The newer the system, the higher chance that it also modulates engine torque as well as applying Left or Right brakes when the wheels spin. Older systems have a dedicated signal wire pair between the ABS/TC module and the engine controller (usually a PWM signal) and newer systems communicate via the CAN bus. Not sure what a '95 A8 uses here... but generally this kind of failure should also set a fault code.

Interface with the TC Lamp. Sometimes hardwired, sometimes via CAN bus. Obviously your light is working

Interface with the TC switch. Sometimes hardwired, sometimes via CAN bus. Given lack of diagnostic codes, I'm wondering if this is a more likley culprit. Most of the systems that I worked on did have diagnostics that would detect a open, shorted, or stuck switch, however maybe a '95 era system does not? Given reliability of mid 90's Audi electrics, might be something to look into.




*** one test I would do, if easy enough, is to find a long stretch of snow or ice, and do a higher speed (if safe!!) 80kph snow or 40kph ice ABS stop all the way down to zero. If your pedal gradually falls towards the floor as the stop progresses - this might indicate wear to the pump/motor portion of the hydraulic unit, rather than focusing you on an electrical problem. (though that said, sometiems the connection between the motor and the electrical controller is external and could be subject to corrosion, if damanged, and the motor isn't getting proper current, could lead to the problem above , and the TC might be smart enough to detect that and disable itself -

In fault modes, ABS in general is left on as long as it can be for safety reasons, even if performance might be less than 100%, where TC is generaly disabled pretty easily with a slight fault.

Sorry this isn't very specific to Audi, but hopefully might help you troubleshoot.
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Old 02-23-2011, 07:48 PM
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