Look in the rear index of the owner's manual, the fss is in there a couple of times. How to reset is in there......
Key out door closed.
Insert key into ignition and turn on
push button 2 times
turn off ign
push and hold button while turn on ign hold this way for 10 sec.
Do all of this in one quick motion .

I call it push push, off ,pushandhold and on

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM