1988 80 Quatt. w/ MT and AC---Differential Lock Up

[Blu]

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Do you happen to know what might be the problem with my car (88 Audi 80 Qua=
tt w/MT and air)? I went to engage the rear differential. The ABS OFF light=
 (on dash.) came on and the rear wheels locked in--as expected. The problem=
 is that now the ABS OFF light will not shut off and the diagram indicator =
(near the emergency brake) will not turn off. The lit arrow on the actual D=
IFF button will turn on and off when I go faster than 15 mph or when the DI=
FF button is depressed. The car itself seems like it has remained with rear=
 differential locked. For instance, the car is difficult to turn at slow sp=
eeds. In addition,  there are two knocks from the front end after the car c=
omes out of the turn. I have driven the car faster than the 15-20 mph and t=
he rear will not disengage. Anything you might know and could pass on would=
 be of great help. By the way, repeatedly pushing either the ABS button in =
center console or the DIFF button near emergency brake seems to do nothing =
other than light and unlight the arrow on the DIFF button.
Thanks
Blu

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