what would cause my ABS light to go on AFTER the wheels start to roll?

[Brett Dikeman]

At 10:27 PM -0400 6/2/03, Obin Olson wrote:
>like the subject what would cause my abs light on the dash to come 
>on after i start the car and roll the wheels...I can sit all day 
>long before I start moving and the light will stay off but about 
>3mph and the light comes on...if I stop at a stoplight and push the 
>abs switch then it will go off till I start moving again...ideas?

Within a few seconds of the car starting to move, the ABS unit does a 
self-test, which includes testing  the ABS actuator unit; if you've 
ever at night noticed the headlights or reverse lights dim a little 
as you start moving, that's what it is.

Wheel sensor mis-positioning and problems with rust buildup on the 
teeth of the hub generally tend to manifest themselves not as a 
failed self test, but as false ABS activation at low speeds.

Once you've done all the checks you can with an ohm-meter on the 
wiring and sensors, the next step is probably to take it to a VW/Audi 
mechanic who has the ABS test unit- although you may only find one 
with a dealer these days.  Without the tester, troubleshooting ABS 
will be a bit like trying to hit a jelly bean with a peashooter in a 
dark room.

Brett
-- 
"They that give up essential liberty to obtain temporary
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