[V8] Intermittent ABS light and diff locking up

[qshipq at aol.com]

 BTDT many times...? Rust gets in the teeth causing the sensor not to count teeth (abs and TCU consider this a wheel that's slower than the others).? IMO, you already have done the diagnostic, whichever sensor is reading higher than the other three, is where you should be concentrating your efforts.? There is nothing magical about putting a wheel up in the air, spinning it at approximately 1 rev per second and measuring the value and comparing it to the others.? That procedure is actually in the Audi ABS diagnostics.? My bet is that the sensor you measured different from the other 3 resting will measure different than the other three with the simulated rolling test.



I would encourage you not to overthink this, there is no magic to the ABS, it's the same abs computer used in every quattro from 1986-1995.? The only unique part of the v8 is that the ABS ecu 'also' sends the speed signals to the TCU for lockup function under acceleration. The TCU is locking up your center diff because there is a difference in the signals, which you already measured - the abs light is coming on because the ABS computer recognizes the same fault. You can replace the suspect sensor with a known good, or you can walk thru the 'other' diagnostics to identify if you have a sensor depth problem or a driveshaft tooth problem, or an intermittent sensor problem.



You could also hunt for the ABS port, or just read vag com from the TCU connection.? The fault diag is as follows

00283 > G47 = Front Left

00285 > G45 = Front Right

00287 > G44 = Rear Right

00290 > G46 = Rear Left



IMO, there is no hit or miss in the symptoms you presented or the diagnostic tree to follow.?? Me I'd put a sensor in the odd measured value you already measured.? If you are looking to do this without a 'known' good, you could swap the sensor to another location and check it there.



Scott J

QSHIPQ Performance Tuning

Chicago





 





 



-----Original Message-----

From: Mark Kalbskopf <gbmarc at cox.net>

To: v8 at audifans.com

Cc: Tony and Lillie <tonyandlillie1 at earthlink.net>; qshipq at aol.com

Sent: Sun, Sep 13, 2009 8:11 pm

Subject: Re: [V8] Intermittent ABS light and diff locking up












Whenever I've looked at the ABS teeth, they just seem to have the usual rough, dusty, slightly rusty surface, but never any major crud or anything.

What I really need is a magical read-out of the signals coming from all 4 wheels while I'm driving.



Otherwise it's a bit of a hit & miss operation, where I replace each sensor in turn until the problem goes away.









Mark.















On Sep 13, 2009, at 4:11 PM, qshipq at aol.com wrote:





 I've cleaned many ABS teeth, and this could definitely be the problem.? On the fronts, you can pull the driveshaft out of the hub enough to clean it without major dis-assembly.? I really doubt trans codes will help you in any way here.? I put up a pretty nerdy post a several months ago on how the center locking works on the v8, and Tony described it again well.? It appears you have a diff lockup signal sent from the trans ecu, caused by one of your abs sensors out of whack with the others.? Fix the signal, you likely won't have a problem.? As a rule, the trans ecu could care less what the actual ABS sensor values are, it's only looking for the differences in them.? The ABS computer on the other hand, is looking for actual value *and* differences between them. 

 

 HTH and my .02

 

 Scott J

 92 v8 4.2 ABT chipped

 

 






=