How does a bad ABS module affect AWD?
#11
12-12-2008, 02:03 PM
I'm pretty sure I'm that friend you're talking about. 
I'll post this up becuase I'm 95% sure that most of you are wrong. (sorry!)
http://en.wikipedia.org/wiki/Quattro..._generation_IV
We have three differentials in our car, a center diff, front diff, and rear diff. The only torsen diff is in the center and that distributes power to the front and rear of the car.
At the front and rear of the car we have open differentials, open diffs send power to whichever tire has the least traction. Audi uses something called EDL (electronic differential lock) to apply the brakes to the slipping wheel (it senses the slipping via the abs system), causing the open diff to send power to the other wheel.
When the ABS system is out, the EDL system is also out because it uses the ABS to sense wheelspin, leaving you with a mechanical center diff and open front and rear diffs.
If I'm wrong, somebody let me know.
Kyle
I'll post this up becuase I'm 95% sure that most of you are wrong. (sorry!)
quattro generation IV
Starting from 1996 on Audi A4 / S4 / RS4 (B5 platform), Audi A6 / S6 / RS6, Audi A8 / S8 with both manual and automatic transmissions. Also on VW Passat B5, where it was initially referred to as syncro, but by the time it reached US soil, it had been re-christened 4motion. Also used on the Volkswagen Phaeton and Volkswagen Group D platform sister vehicles; also the Volkswagen Touareg where they use separate transmissions, PTU's and front axles.
The manually locking rear differential from the earlier generations was replaced with a conventional open differential, with "Electronic Differential Lock" (EDL) (which, detects wheelspin via ABS road wheel speed sensors, and applies brakes to the one spinning wheel, thus transferring torque via open differential to the opposite wheel which has more traction). EDL works at speeds up to 80 km/h (50 mph) on all quattro models (on non-quattro models: up to 40 km/h (25 mph).
System type: Permanent four-wheel drive.
Torsen T-2 centre differential, 50:50 'default' split, automatically apportioning up to 75% of torque transfer to either front or rear axle.
Open rear differential, Electronic Differential Lock (EDL).[4]
Open front differential, Electronic Differential Lock (EDL).[4]
How does the system perform: In on-road conditions the car will not be able to move if all four wheels lose traction altogether. Torsen effect with one wheel losing traction and spinning freely will not happen on quattro IV because EDL will apply brakes to the spinning wheel, and Torsen differential will transfer torque to another axle. However, in severe road conditions (wheels on ice or raised in the air and an obstacle restricting the vehicle from moving forward, on a slope) the car will not be able to move when one front and one rear wheel lose traction. EDL will brake the single spinning wheel on an axle trying to transfer torque to the opposite wheel, but because Audi's EDL action is too "soft" it is not able to brake the wheel to the full stop. The car will end up spinning one front and one rear wheels but not moving forward.
Starting from 1996 on Audi A4 / S4 / RS4 (B5 platform), Audi A6 / S6 / RS6, Audi A8 / S8 with both manual and automatic transmissions. Also on VW Passat B5, where it was initially referred to as syncro, but by the time it reached US soil, it had been re-christened 4motion. Also used on the Volkswagen Phaeton and Volkswagen Group D platform sister vehicles; also the Volkswagen Touareg where they use separate transmissions, PTU's and front axles.
The manually locking rear differential from the earlier generations was replaced with a conventional open differential, with "Electronic Differential Lock" (EDL) (which, detects wheelspin via ABS road wheel speed sensors, and applies brakes to the one spinning wheel, thus transferring torque via open differential to the opposite wheel which has more traction). EDL works at speeds up to 80 km/h (50 mph) on all quattro models (on non-quattro models: up to 40 km/h (25 mph).
System type: Permanent four-wheel drive.
Torsen T-2 centre differential, 50:50 'default' split, automatically apportioning up to 75% of torque transfer to either front or rear axle.
Open rear differential, Electronic Differential Lock (EDL).[4]
Open front differential, Electronic Differential Lock (EDL).[4]
How does the system perform: In on-road conditions the car will not be able to move if all four wheels lose traction altogether. Torsen effect with one wheel losing traction and spinning freely will not happen on quattro IV because EDL will apply brakes to the spinning wheel, and Torsen differential will transfer torque to another axle. However, in severe road conditions (wheels on ice or raised in the air and an obstacle restricting the vehicle from moving forward, on a slope) the car will not be able to move when one front and one rear wheel lose traction. EDL will brake the single spinning wheel on an axle trying to transfer torque to the opposite wheel, but because Audi's EDL action is too "soft" it is not able to brake the wheel to the full stop. The car will end up spinning one front and one rear wheels but not moving forward.
We have three differentials in our car, a center diff, front diff, and rear diff. The only torsen diff is in the center and that distributes power to the front and rear of the car.
At the front and rear of the car we have open differentials, open diffs send power to whichever tire has the least traction. Audi uses something called EDL (electronic differential lock) to apply the brakes to the slipping wheel (it senses the slipping via the abs system), causing the open diff to send power to the other wheel.
When the ABS system is out, the EDL system is also out because it uses the ABS to sense wheelspin, leaving you with a mechanical center diff and open front and rear diffs.
If I'm wrong, somebody let me know.
Kyle
#12
12-12-2008, 03:21 PM
Kyle I am with you. I haven't chimed in yet because everyone mostly agreed on the system but from everything that I have read and heard about the quattro system is it is electronicly controlled. Weather it works in conjunction with the ABS I don't know that for sure but after reading the quote it would make sense for it to work that way.
Side note-Is the module located under the rear seat?
Side note-Is the module located under the rear seat?
#13
12-12-2008, 03:24 PM
ABS control module is right next to the main washer fluid tank and power steering fluid reservoir.
#14
12-12-2008, 04:06 PM
+1 for Kyle
Here's another source on quattro, the dates appear to be for European models, the IV generation uses ABS for EDL
http://www.audiv8.eu/specifications/quattro/
Here's another source on quattro, the dates appear to be for European models, the IV generation uses ABS for EDL
http://www.audiv8.eu/specifications/quattro/
#18
12-13-2008, 02:45 AM
I put in an ABS switch to disable my ABS for drifting (stopping quicker when horizontal)... and if I can whip around without ABS/EDL I forsure have more than 2wd FWD, and since i can pull it horizontal as long as I want its AWD just without EDL. The power to the wheels just isnt being transfered for the best traction without EDL there to lock the differential.
#20
12-13-2008, 09:23 PM
No, sir. I stand corrected. The B5 center diff is a mechanical Torsen. The front and rear diffs of a B5 Quattro are open and electronically locked by the EDL. I'm a bit embarrassed I couldn't even remember this because I serviced these cars in a dealer. 