Automatic Locking Differential. As per the 1993 owners manual,

" The automatic locking differential engages when there is a difference in speed (slip)during accelaration between the front and rear wheels of over 1.2 MPH and the vehicle speed is less than 15.6 MPH. It will disengage at speeds above 16.2 MPH".

It also says bring it in to the dealer if the light stays on. My car is an 84 so I am not familiar with that system.

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Patrick Leber
'84 190E 2.3
'83 Porsche 944 (track car)
'84 Porsche 944 (parts car)
85.5 Porsche 944 (sled)